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1. Introduction
1. One of the problems in understanding evolution is that it may be defined in different ways. According to the Random House Webster's College Dictionary (1999), biological evolution is a change in the genetic makeup of a population from generation to generation. It may also be defined as the development of species or other groups of organisms (genera and families) from earlier forms by natural selection. Microevolution refers to changes at or below the species level, while macroevolution generally refers to large-scale changes over a long period of time resulting in new species. In this article I have attempted to clarify and summarize some of the major concepts and terms used by evolution scientists. Depending on the author, evolution may be referred to as a theory, hypothesis, law, truth, and fact. In fact, these terms are often used interchangeably and sometimes incorrectly, even by prestigious biologists. In my opinion, evolution is a well-established scientific theory supported by facts. For science teachers, I have included an extensive bibliography and a crossword puzzle containing many of the terms defined in this article.

   The noun evolution is derived from the verb evolve, meaning to gradually change with time. Evolution can be defined in several different ways. For example, Wayne's Word has evolved from a humorous, natural history newsletter sent out to friends, to a large on-line, hyperlinked, peer-reviewed textbook of natural history with millions of hits per month. Another definition is organic (biological) evolution that incorporates numerous facts and well-substantiated, tested hypotheses. It is usually associated with natural selection based on the original published work of Charles Darwin and Alfred Russel Wallace.

   Try The Wayne's Word Evolution Crossword Puzzle

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   2. Is Evolution a Theory or a Fact?

   Four Important Definitions Used In The Teaching Of Science: Working Group on Teaching Evolution, National Academy of Sciences (1998) Fact: In science, an observation that has been repeatedly confirmed. Law: A descriptive generalization about how some aspect of the natural world behaves under stated circumstances. Laws can be very useful in supporting hypotheses and theories, but like all elements of science they can be altered with new information and observations. Hypothesis: A testable statement about the natural world that can be used to build more complex inferences and explanations, such as a scientific theory. Theory: In science, a well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses.

2. In November 2004, suburban Atlanta biology textbooks included a warning sticker that said:

   "This textbook contains material on evolution. Evolution is a theory, not a fact, regarding the origin of living things. This material should be approached with an open mind, studied carefully and critically considered."

3. On November 19, 2004, the Dover School Board of Pennsylvania passed a resolution requiring teachers to read a statement to students in 9th grade science classes endorsing intelligent design as an alternative explanation for the origin of life.

   "The Pennsylvania Academic Standards require students to learn about Darwin's Theory of Evolution and eventually to take a standardized test of which evolution is a part. Because Darwin's Theory is a theory, it continues to be tested as new evidence is discovered. The Theory is not a fact. Gaps in the Theory exist for which there is no evidence. A theory is defined as a well-tested explanation that unifies a broad range of observations. Intelligent Design is an explanation of the origin of life that differs from Darwin's view. The reference book, Of Pandas and People, is available for students who might be interested in gaining an understanding of what Intelligent Design actually involves. With respect to any theory, students are encouraged to keep an open mind. The school leaves the discussion of the Origins of Life to individual students and their families. As a Standards-driven district, class instruction focuses upon preparing students to achieve proficiency on Standards-based assessments."

4. The resolution was challenged a year later in the United States federal courts: Case No. 04cv2688, "Tammy Kitzmiller et al v Dover Area School District." The plaintiffs successfully argued that intelligent design is a form of creationism, and that the school board policy thus violated the Establishment Clause of the First Amendment to the United States Constitution.

5. The argument whether evolution is a theory or a fact is an invalid comparison. Evolution is a scientific theory that has explained the factual evidence of scientists for more than a century. All interpretations of facts in science are provisional and subject to challenge. Under a strict definition, a scientific theory should not be called a "fact" even though it explains all known facts and has survived the test of time. There is always the possibility that a scientific theory will be updated or changed as new evidence is discovered. The theory of evolution assumes the existence of life and is directed to an explanation of how life evolved. It does not deal with the origin of life, and it does not presuppose the absence of a creator or God. Although the origin of life is often included in debates about evolution, it is a very different topic that does not have all the empirical evidence of biological evolution. Scientific explanations for the origin of life are more properly referred to as hypotheses rather than scientific theories. Intelligent design is a non-scientific argument or assertion that life "owes its origin to a master intellect." Please refer to Origin of Life later in this this discussion.

6. According to E.C. Scott (Evolution vs. Creationism, Univ. of Calif. Press, 2004), most people consider facts more important than hypotheses, theories and laws. In fact, they rank these terms in order of importance as follows: Facts-Laws-Theories-Hypotheses. Scientists rank these terms in the following order from most important to least important: Theories-Laws-Hypotheses-Facts. Facts are certainly not set in stone and are often changed in science. Consider the number of chromosomes in a human somatic cell. In the 1950s the number was determined to be 48. This fact was published in all biology textbooks. With better techniques in staining chromosomes, the number was later revised to 46, 23 from each parent. Disagreement on chromosome numbers still occurs to this day, particularly with plant species containing numerous chromosomes that often overlap each other making accurate counts very difficult. For as long as I can remember, Pluto has been listed as the ninth planet in our solar system. Recent studies of its orbital patterns and other factors indicate that Pluto is not a true planet compared with Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

7. There is compelling evidence to show that humans once had 24 pairs of chromosomes (2n = 48) like present-day great apes (orangutans, gorillas and chimpanzees). Like all other 23 chromosomes, chromosome #2 has a terminal genetic marker called a telomere. Telomeres shorten prior to chromosome replication and cell division. Shortened telomeres eventually signal the cell to stop dividing. In cancer cells, an enzyme called telomerase keeps telomeres at a constant length so that cancer cells keep on dividing over and over again. Chromosome #2 has a second telomere in the middle region, indicating that two chromosomes joined together end-to-end an became permanently fused into chromosome. The sister chromatids of a chromosome doublet are attached in a constricted region of the chromosome called the centromere. Each chromosome has a single centromere; however, chromosome #2 has two centromeres, further evidence that it represents two fused chromosome doublets, each with its own centromere.

   Diagram of Chromosome Doublet Showing Centromere

8. Some biologists say that evolution is a scientific theory and a fact. According to T. Ryan Gregory of the Department of Integrative Biology, University of Guelph, Ontario, Canada (2007), the notion that species may change through time and that living organisms are related to one another through common descent is a fact. He also states that evolution is a well-established scientific theory. "That evolution is a theory in the proper scientific sense means that there is both a fact of evolution to be explained and a well-supported mechanistic framework to account for it. To claim that evolution is "just a theory" is to reveal both a profound ignorance of modern biological knowledge and a deep misunderstanding of the basic nature of science."

9. The eminent evolutionary biologist Ernst Mayr also considers evolution to be a fact. In his book What Evolution Is (2001), he gives the following explanation:

   Is Evolution A Fact? "Evolution is not merely an idea, a theory, or a concept, but is the name of a process in nature, the occurrence of which can be documented by mountains of evidence that nobody has been able to refute. Some of this evidence was summarized in Chapters 1-3. It is now actually misleading to refer to evolution as a theory, considering the massive evidence that has been discovered over the last 140 years documenting its existence. Evolution is no longer a theory, it is simply a fact."

10. The Working Group on Teaching Evolution, National Academy of Sciences (1998) defines a scientific theory as a well-substantiated explanation of some aspect of the natural world than can incorporate facts, laws, inferences, and tested hypotheses. Like "theory," the word "fact" has a different meaning in science than it does in common usage. A scientific fact is an observation that has been confirmed over and over. However, observations are gathered by our senses, which can never be trusted entirely. Observations also can change with better technologies or with better ways of looking at data. Please refer to paragraph 6 which discusses the erroneous human chromosome number of 48 and the planet Pluto. "Ironically, facts in science often are more susceptible to change than theories--which is one reason why the word "fact" is not much used in science."

11. Eugenie C. Scott of the National Center For Science Education defines "facts" of evolution in the following paragraph:

    "From the standpoint of philosophy of science, the "facts of evolution" are things like the anatomical structural homologies such as the tetrapod forelimb, or the biochemical homologies of cross species protein and DNA comparisons, or the biogeographical distributions of plants and animals. The "facts of evolution" are observations, confirmed over and over, such as the presence and/or absence of particular fossils in particular strata of the geologic column (one never finds mammals in the Devonian, for example). From these confirmed observations we develop an explanation, an inference, that what explains all of these facts is that species have had histories, and that descent with modification has taken place. Evolution is thus a theory, and one of the most powerful theories in science."

12. Richard Dawkins presents his case for why evolution should be called a fact rather than a theory in his book The Greatest Show on Earth: The Evidence For Evolution (2009). He refers to two kinds of theories: Well established scientific theories and laymen theories or tentative hypotheses. In fact, Dawkins compares a scientific theory with the mathematician's theorem, and proposes that scientific theory be replaced with the word "theorum." Two words with the same pronunciation and with different meanings and slightly different spellings will require even more clarification by writers and lecturers. In my opinion, capitalizing the word Theory for scientific theory would serve the same purpose, or better yet, just say scientific theory.

13. All of these discussions of whether evolution is a theory or a fact depend on how the terms "theory" and "fact" are defined. The "fact" that living organisms change with time is undeniable; however, in my opinion, evolution is best explained as a well-established scientific theory based on numerous facts. The position of Wayne's Word in teaching evolution is summarized by the Steering Committee on Science and Creationism, National Academy of Sciences (1999):

    "The contention that evolution should be taught as a "theory, not as a fact" confuses the common use of these words with the scientific use. In science, theories do not turn into facts through the accumulation of evidence. Rather, theories are the end points of science. They are understandings that develop from extensive observation, experimentation, and creative reflection. They incorporate a large body of scientific facts, laws, tested hypotheses, and logical inferences. In a sense, evolution is one of the strongest and most useful scientific theories we have."

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    3. Evidence For Genetic Variability In Populations

14. In order to have changes in populations of organisms it is necessary to have a source for the genetic variability. There are at least five sources of genetic variability in populations: (1) DNA mutations or changes in existing genes and the formation of new genes. (2) Reshuffling of chromosomes and genes during meiosis and sexual reproduction, including crossing over and transposons. (3) Natural selection for favorable traits, and selection against undesirable genes. (4) Interbreeding between genetically different populations, including emigration and immigration. (5) Genetic drift in relatively small, isolated populations.

    Details Of Mitosis & Meiosis An Introduction To Transposons  Population Genetics & Genetic Drift

15. There is ample evidence from field observations and DNA studies in laboratories to show that genetic variation occurs within populations of plants and animals. These are undeniable facts. The degree of variability is reflected in different levels of organization (taxonomic hierarchies), such as families, genera and species. DNA variations can be induced in the laboratory using mutagenic agents, such as strong chemical oxidizing agents and high energy radiation. Genetic variation can be readily observed in pathogenic bacteria that defy medical science by rapidly changing into new forms that are resistant to the latest antibiotics. HIV disguises itself from our highly evolved immune system and even acquires resistance to antiviral drugs, such as AZT. New strains of influenza viruses develop each year In fact, our war on pathogenic microbes has accelerated the process of microevolution in these organisms. Genetic variability is the raw material for this evolution. A thorough understanding of the genetics and evolution of pathogenic microorganisms may be crucial to the survival of the human race.

16. DNA sequences coding for essential components of cellular metabolism, such as ribosomal subunits, are highly conserved, varying little between major groups of organisms. Highly conserved genes are very stable because changes in their DNA (mutations) are usually detrimental. Genes that are not highly conserved are subject to mutations and are important factors in natural selection and the evolution of new species. Some isolated species populations have unique traits correlated with geographic distribution. These populations are called subspecies, and their unique genetic changes have occurred through long periods of isolation. Varieties are similar to subspecies, but are not necessarily geographically isolated. Sometimes variation within a species complex makes identification very difficult. This is particularly true when the variable traits are apparently not under selection pressure and cannot be correlated with geographic distribution. One case in point is the California species known as BTK (Brodiaea terrestris ssp. kernensis), native to grasslands from Kern and Santa Barbara counties to the Mexican border. Most Brodiaea species have three sterile stamens called staminodes. Variants of BTK have staminodes that are hooded (curved inwardly at apex), staminodes that are flattened and strap-shaped or inrolled along upper margins, and narrow staminodes that are tapered toward the apex. In addition, the staminodes may be erect, leaning slightly outward or leaning inward. Taxonomists have named some of the variants as new species or varieties; however, data from Principal Components Analysis (PCA) thus far indicates that BTK is one variable species complex that does not warrant segregation. In fact, BTK intergrades into variable populations on the Santa Rosa Plateau of Riverside County.
    

    Staminode variation in BTK (Brodiaea terrestris ssp. kernensis): A. Otay Mtn (San Diego County), B. San Marcos (San Diego County), C. Sierra Nevada (Kern County), D. Gaviota Pass (Santa Barbara County), E. Santa Rosa Plateau (Riverside County).

17. The primary explanation for the astonishing variety of life on earth is the amazing genetic molecule called DNA (deoxyribonucleic acid). DNA has been metaphorically described as a long, twisted ladder with literally millions of rungs composed of the base pairs: adenine (A) with thymine (T) and guanine (G) with cytosine(C). Each rung has 4 possible arrangements: A-T, T-A, C-G, and G-C. A DNA molecule with five billion base pairs has 4^{5,000,000,000} or 10^{3,000,000,000} different possible base sequences. This astronomical number has three billion digits and would fill about one million pages on a computer printout (12 cpi). This incredible number helps to explain the enormous diversity of life forms, from viruses and bacteria to complex plants and people, all genetically programmed by DNA. Flowering plants alone range from tiny wolffias less than one millimeter long to huge eucalyptus trees over 100 meters tall. The potential variability and mutability of DNA make it a perfect mechanism for evolution.

18. DNA bases are to proteins as letters are to words. Different rearrangements and sequences result in numerous different proteins and words. Even a mutation in the DNA involving only one misplaced base (point mutation) may have a significant effect on the organism, particularly if this gene results in a crucial protein, such as a vital enzyme. A good analogy of a point mutation is a missplaced letter in a word. Like a point mutation in DNA, a one-letter substitution in a word can sometimes completely change the meaning of the sentence. This is especially true when speaking or writing in another language. In a store in Costa Rica I discovered that I had no Costa Rican currency called colones, only U.S. dollars. In my meager attempt to communicate with the clerk in Spanish, I told her that I had no "cojones," inadvertently substituting a "j" for an "l." When she replied: "I am sorry for you," I knew that my sentence was corrupted. In a vulgar translation, I essentially told the woman that I had no testicles! In this case, a one letter substitution (mutation) completely changed the meaning of the sentence.
    Table of DNA Base Triplets That Code For Specific Amino Acids

    Amino Acid	DNA Base Triplets	M-RNA Codons	T-RNA Anticodons
    alanine	CGA, CGG, CGT, CGC	GCU, GCC, GCA, GCG	CGA, CGG, CGU, CGC
    arginine	GCA, GCG, GCT, GCC TCT, TCC	CGU, CGC, CGA, CGG AGA, AGG	GCA, GCG, GCU, GCC UCU, UCC
    asparagine	TTA, TTG	AAU, AAC	UUA, UUG
    aspartate	CTA, CTG	GAU, GAC	CUA, CUG
    cysteine	ACA, ACG	UGU, UGC	ACA, ACG
    glutamate	CTT, CTC	GAA, GAG	CUU, CUC
    glutamine	GTT, GTC	CAA, CAG	GUU, GUC
    glycine	CCA, CCG, CCT, CCC	GGU, GGC, GGA, GGG	CCA, CCG, CCU, CCC
    histidine	GTA, GTG	CAU, CAC	GUA, GUG
    isoleucine	TAA, TAG, TAT	AUU, AUC, AUA	UAA, UAG, UAU
    leucine	AAT, AAC, GAA, GAG GAT, GAC	UUA, UUG, CUU, CUC CUA, CUG	AAU, AAC, GAA, GAG GAU, GAC
    lysine	TTT, TTC	AAA, AAG	UUU, UUC
    methionine	TAC	AUG	UAC
    phenylalanine	AAA, AAG	UUU, UUC	AAA, AAG
    proline	GGA, GGG, GGT, GGC	CCU, CCC, CCA, CCG	GGA, GGG, GGU, GGC
    serine	AGA, AGG, AGT, AGC TCA, TCG	UCU, UCC, UCA, UCG AGU, AGC	AGA, AGG, AGU, AGC UCA, UCG
    stop	ATG, ATT, ACT	UAA, UAG, UGA	AUG, AUU, ACU
    threonine	TGA, TGG, TGT, TGC	ACU, ACC, ACA, ACG	UGA, UGG, UGU, UGC
    tryptophan	ACC	UGG	ACC
    tyrosine	ATA, ATG	UAU, UAC	AUA, AUG
    valine	CAA, CAG, CAT, CAC	GUU, GUC, GUA, GUG	CAA, CAG, CAU, CAC

    A Computer Screen Filled With DNA Code An Introduction To DNA Structure & Function Introduction To Polymerase Chain Reaction (PCR)  Remarkable Diversity Of Flowering Plants On Earth

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    4. Gene Duplication: The Formation of New Genes

19. In the previous section, mutations were listed as a source of genetic variability by the formation of new genes. Gene duplication plays such an important role in evolution that I have included a separate section about it. Gene duplication may involve single genes, chromosomes or the entire genome. It may be caused by translocations on the same chromosome, or by an error in the pairing of homologous chromosomes during meiosis where sister chromatids are out of alignment. Unequal crossing over can result is cells receiving extra genes and cells with deleted genes. Gene duplication in the laboratory is accomplished by the polymerase chain reaction (PCR). Using the PCR technique a single gene can be amplified or cloned into millions of duplicate copies. Plants are the most prolific gene duplicaters because they commonly form polyploids with multiple sets of the original base number of chromosomes. Most of our fruits and vegetables are polyploids, not to mention numerous wildflower species throughout the state of California.
    

    Simplified explanation for chromosome duplication during mitosis of a typical plant cell. In normal mitosis, the chromosome doublets separate during anaphase so that each of the daughter cells (far right) receives the exact same chromosome number as the original mother cell, i.e. four single chromosomes: two red and two blue. In this case, the anaphase cell divided into two daughter cells after the chromosome doublets had already separated into single chromosomes (i.e. chromatids separated). In other words, the spindle dissolved, leaving the cell with eight single chromosomes. These became doublets and the cell divided into two daughter cells each containing eight single chromosomes: four red and four blue. This phenomenon can be induced by the alkaloid colchicine.

    Polyploidy & Hybridization in California  The Major Details Of Mitosis & Meiosis

20. According to Soltis, et al. (2003), old genomes that are polyploid with respect to the base number and amount of genetic material, may function as diploids with respect to the level of gene expression and chromosomal characteristics. These "old polyploids" may have become "diploidized" by the loss, mutation or suppression of duplicate genes. Other causes for diploidization may include genomic rearrangements and transposons. This can drastically change the chromosome properties of a species. For example, an odd polyploid with a base number of six might have a sporophyte number of 5n = 30. This pentaploid would tend to be sterile because of an odd chromosome set at synapsis of prophase I. However, if this plant behaves as a diploid with 2n = 30, it would be fertile with two sets of 15 chromosomes during meiosis. It would simply have a diploid (sporophyte) number of 2n = 30 and a haploid (gametophyte) number of n = 15. Diploidization has apparently occurred in the California genus Brodiaea. In fact, populations of B. terrestris ssp. kernensis in Kern County have a diploid chromosome number of 48, higher than a human somatic cell.

    Index Of Brodiaea Pages On Wayne's Word  Images Of Brodiaea Species In California

21. Athough polyploid plants often have more chromosomes than people, the morphological complexity of an organism is certainly not reflected by the number of genes or DNA base pairs. For example, according to Gerald Tuskan of Oak Ridge National Laboratory, Tennessee (2006), the black cottonwood (Populus trichocarpa) genome has now been determined. His team identified more than 45,000 putative protein-coding genes. The Human Genome Project is a worldwide endeavor to map the DNA base sequence of every gene in the human genome. The total number of functional genes is considerably less than expected, about 30,000 genes per cell compared with previous estimates of 100,000 genes per cell. It has been estimated that a human somatic cell contains about 5 billion base pairs. If the average gene contains 1500 bases, then 30,000 functional genes is only about one percent of the total DNA per cell. It seems that some of this extra DNA came from gene duplication.

22. The two genes that exist after gene duplication are called paralogs and usually code for proteins with a different function and/or structure. The second copy of the gene may be under less selective pressure because mutations of it have no deleterious effects on the host organism. Therefore, it mutates faster than a functional single-copy gene over generations of organisms. It should be noted here that gene duplication may not be passed on if it occurs in somatic cells. In addition, the duplication of oncogenes are known to be a common cause of certain types of cancer. The overall advantage of gene duplication is greatly increased genetic variability, the raw material for evolution. One of the truly remarkable examples of gene duplication is in the antibody mediated immune system of animals. How can we produce a seemingly endless array of germ-fighting antibody proteins in response to an infection?
    

    Immune (IgG) antibody model composed of four polypeptides: Two heavy (H) chains (longer green), and two light (L) chains (shorter blue). The two combining sites where the antibody "arms" attach to antigens are shown in red. Using this model, a separate gene for every antibody protein is not necessary. 1,000 genes could produce 1,000 different L chains and 1,000 genes could produce 1,000 different H chains. With 2,000 genes 1,0002 or 1,000,000 different antibodies could be produced, simply by using different combinations of H chains and L chains. This may explain how organisms can produce antibodies against different antigens, even synthetic antigen proteins that animals have never been exposed to. Using this model, animals would not need separate genes for every antigen that they will ever encounter, they simply manufacture millions of different possible antibodies from a given number of genes for L chains and H chains. The reservoir of L and H chains comes from gene duplication.

23. Another example of gene duplication is the evolution of color vision (trichromacy) in higher primates. [See G.H. Jacobs and J. Nathans Scientific American 300 (4): 56-63, April 2009.] This remarkable property of human vision is possible because the retina (the layer of nerve cells in the eye that captures light and transmits visual information to the brain) uses only three types of light-absorbing pigments for color vision. Each individual cone cell in the retina contains genes for all three color pigments, but randomly selects only one of the three to activate and shuts down the other two. The M and L pigment genes reside on the X chromosome, and a third S pigment gene is located on chromosome #7. Each of the three pigments absorbs light from a particular region of the spectrum and collectively produce a wide range of color vision. The pigments absorb light of different wavelengths that we perceive as yellow, green and blue. This phenomenon is similar to the the mixing of red, green and blue pixels to generate a full spectrum of color in computer monitors. The following table shows 216 color combinations produced from three colors using a six character hexadecimal HTML code:
    Different Colors Produced By 6 Character HTML Hexadecimal Code
    216 Color Combinations From 000000 (black) to ffffff (white)

    000000

    000033

    000066

    000099

    0000cc

    0000ff

    006600

    006633

    006666

    006699

    0066cc

    0066ff

    00cc00

    00cc33

    00cc66

    00cc99

    00cccc

    00ccff

    003300

    003333

    003366

    003399

    0033cc

    0033ff

    009900

    009933

    009966

    009999

    0099cc

    0099ff

    00ff00

    00ff33

    00ff66

    00ff99

    00ffcc

    00ffff

    330000

    330033

    330066

    330099

    3300cc

    3300ff

    336600

    336633

    336666

    336699

    3366cc

    3366ff

    33cc00

    33cc33

    33cc66

    33cc99

    33cccc

    33ccff

    333300

    333333

    333366

    333399

    3333cc

    3333ff

    339900

    339933

    339966

    339999

    3399cc

    3399ff

    33ff00

    33ff33

    33ff66

    33ff99

    33ffcc

    33ffff

    660000

    660033

    660066

    660099

    6600cc

    6600ff

    666600

    666633

    666666

    666699

    6666cc

    6666ff

    66cc00

    66cc33

    66cc66

    66cc99

    66cccc

    66ccff

    663300

    663333

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    663399

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    669900

    669933

    669966

    669999

    6699cc

    6699ff

    66ff00

    66ff33

    66ff66

    66ff99

    66ffcc

    66ffff

    990000

    990033

    990066

    990099

    9900cc

    9900ff

    996600

    996633

    996666

    996699

    9966cc

    9966ff

    99cc00

    99cc33

    99cc66

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    999900

    999933

    999966

    999999

    9999cc

    9999ff

    99ff00

    99ff33

    99ff66

    99ff99

    99ffcc

    99ffff

    cc0000

    cc0033

    cc0066

    cc0099

    cc00cc

    cc00ff

    cc6600

    cc6633

    cc6666

    cc6699

    cc66cc

    cc66ff

    cccc00

    cccc33

    cccc66

    cccc99

    cccccc

    ccccff

    cc3300

    cc3333

    cc3366

    cc3399

    cc33cc

    cc33ff

    cc9900

    cc9933

    cc9966

    cc9999

    cc99cc

    cc99ff

    ccff00

    ccff33

    ccff66

    ccff99

    ccffcc

    ccffff

    ff0000

    ff0033

    ff0066

    ff0099

    ff00cc

    ff00ff

    ff6600

    ff6633

    ff6666

    ff6699

    ff66cc

    ff66ff

    ffcc00

    ffcc33

    ffcc66

    ffcc99

    ffcccc

    ffccff

    ff3300

    ff3333

    ff3366

    ff3399

    ff33cc

    ff33ff

    ff9900

    ff9933

    ff9966

    ff9999

    ff99cc

    ff99ff

    ffff00

    ffff33

    ffff66

    ffff99

    ffffcc

    ffffff

24. Most nonprimate mammals exhibit dichromacy, with color vision based on just two kinds of visual pigments. These animals do not have full color vision. Although the mechanism of gene inactivation is slightly different in Old and New World primates, the evolution of trichromacy enabled these mammals to see a technicolor world of flowers, fruits and insects. This is somewhat analogous to the evolution of high resolution color monitors from the drab monochrome green and amber progenitors. One obvious advantage of trichromacy is being able to clearly distinguish the subtle shades of ripening fruit from surrounding vegetation.

25. Color blindness or the inability to differentiate between certain color variations is more common in men because they have only one X chromosome. If defective M and L pigment genes reside on their single X chromosome, men will exhibit this trait. Women have two X chromosomes and therefore can be homozygous or heterozygous for the color blind trait. The phenomenon of X inactivation complicates the expression of color blindness in heterozygous females since only one X is functional and the other remains inactive as a Barr body. The inactivation of X chromosomes appears to be a random event.

    The Inheritance Of Color Blindness In Humans

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    5. Evolution & Irreducible Complexity

26. Coagulation or the clotting of blood is a complex process which evolved from repetitive gene duplication. It involves platelets and the clotting protein fibrin plus a series of enzymatic reactions called the coagulation cascade. Disorders of coagulation can lead to an increased risk of bleeding (hemorrhage) and/or clotting (thrombosis). So crucial is this elaborate cascade, that one failed protein can disrupt the entire process. Intelligent design advocate Michael Behe (1996) has argued that coagulation is an example of irreducible complexity, where less complex models simply could not exist. In other words, each and every element of the complex cascade of enzymes and cofactors must be in place for blood clotting to work. According to Behe (Darwin's Black Box, 1996), an irreducibly complex system cannot be produced by Darwinian natural selection, and must have been "designed." However, Kenneth Miller ( Finding Darwin's God, 1999) discusses Russell Doolittle's pioneering work on protein evolution and the mechanism of blood coagulation. Miller describes a simpler blood clotting system in a lobster whose step-by-step evolution is relatively easy to account for. Behe also uses irreducible complexity in his description of the common mousetrap, an oversimplified argument that has been clearly refuted by other scientists. In fact, please refer to the following web pages by Keith Robison (1996) and John H. McDonald (2002).

    Irreducible Complexity or Irreproducible Irreducibility  Animations Showing A Reducibly Complex Mousetrap

27. Another example of irreducible complexity that is often used by advocates of intelligent design is the remarkable bombardier beetle (Brachinus). How could such a complex and potentially lethal mechanism for repelling predators be produced by natural selection? This suborder of beetles known as Adephaga secrete a number of chemicals for a variety of purposes, only one of which is defense. Bombardier beetles inject an explosive mixture of hydroquinone, hydrogen peroxide plus several potent catalysts into a reaction chamber in the abdomen. Catalase breaks down the hydrogen peroxide into water and oxygen gas. Peroxidase oxidizes hydroquinone into benzoquinone. The mixture of chemicals and enzymes volatilizes instantly upon contact with the air, generating a puff of "smoke"" and an audible popping sound. This caustic flatulence is totally controlled by the beetle, otherwise it might accidentally blow up its rear end. The explosive discharge apparently discourages predators, either by chemical irritation, heat or repugnance. The temperature of the explosive mixture of gasses and fluids is over 100 degrees Celsius, the boiling point of water. This astonishing chemical defense mechanism is discussed by D.J. Aneshansley and T. Eisner (1969) in Science Vol. 165: 61-63.
    

    Bombardier beetles of the genus Brachinus, a member of the large ground beetle family (Carabidae). These small beetles are about 13 mm long (1/2 inch). They are fairly common in southern California, particularly near streams, lakes and marshy areas. The wing covers (elytra) are dark blue-brown with a contrasting reddish-orange head and prothorax.

28. Other arthropods also produce some of the same chemicals found in bombardier beetles. Like bombardier beetles, these chemicals are used for defense or make the animal distasteful to predators; however, the mechanisms are not as sophisticated as bombardier beetles. Starting with these simpler mechanisms, a plausible step-by-step microevolutionary pathway culminating in bombardier beetles can be constructed. In fact, Mark Isaak (2003) discusses this in his on-line article entitled: "Bombardier Beetles and the Argument of Design."

    The Origin Of Eyes In Distantly Related Animals

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    6. Scientific Theory vs. Common Theory

29. A scientific theory is a testable explanation about the cause or causes of a broad range of related phenomena. It remains open to tests, revision, and tentative acceptance or rejection. It should not be confused with a common layman theory or proposition that has not been scrutinized by the scientific method. In the scientific method, a hypothesis or tentative explanation is formulated to explain an observation or phenomenon. This is a good example of inductive reasoning where a general conclusion (hypothesis) is based on specific observations or data. Then an attempt is made to prove or disprove the hypothesis through detailed research and experimentation. Successful results by one scientist does not automatically turn a hypothesis into a theory. "One scientist cannot create a scientific theory; he or she can only create a hypothesis." Only after repeated tests by other scientists who arrive at similar conclusions does a hypothesis become a scientific theory. Evolution is not merely a common theory or "only a theory" as some people state in their commentaries. It is a scientific theory based on more than a century of research by thousands of dedicated scientists from throughout the world.

30. Biological evolution has considerable empirical evidence, and it is testable and verifiable. It fits the definition of a true scientific theory. Under a strict definition, a scientific theory should not be called a "fact" even though it explains all known facts and has survived the test of time (more than a century in the case of evolution). There is always the possibility that a scientific theory will be updated or changed as new evidence is discovered. The sticker placed in biology textbooks in Atlanta is poorly worded. It implies that evolution is just another "common theory," a tentative statement that attempts to explain something without any factual proof. A common theory has a popular meaning, which is roughly equivalent to an "educated guess" or "hunch." The label should say "scientific theory" rather than theory. In addition, the dichotomous comparison of a scientific theory with the word "fact" is incorrect.

31. As stated above, all interpretations of facts in science are provisional and subject to challenge. Physicists never refer to any theory as a "fact," and always leave open the possibility that any theory will be found to be incomplete or needing revision, even though it fits all known facts and has passed all tests so far. It is still Einstein's theory of relativity, even though it is probably as close to a fact as anyone can get in science. It has been tested every day in many ways and has survived. Some day we may find a more complete theory that explains and predicts relativity even better than Einstein's theory. The noun "theory" associated with time-tested explanations, such as evolution, relativity and plate tectonics, should be modified by the adjective "scientific" in order to distinguish it from a "common" or "layman" theory that is essentially a tentative explanation or untested hypothesis. In fact, it would be better to capitalize the word theory when it refers to a scientific theory. [For example, gram calories and dietary Calories are spelled the same, except that a dieter's Calorie is capitalized and actually refers to a kilocalorie!]

32. It should be noted here that a hypothesis does not always become a scientific theory. Here is an example: A botanist discovers a wildflower population that appears different from all other known species of a particular genus. His hypothesis states that this is a new (undescribed) species unknown to science. To prove this hypothesis it is necessary to collect numerous detailed measurements of the floral and vegetative parts and to conduct an extensive search of the literature and herbaria. A type specimen (holotype) of the plant is deposited in an internationally recognized herbarium. Duplicated specimens (isotypes) are deposited in other herbaria. The hypothesis is confirmed by statistical analysis of the data, including PCA (principal components analysis). The results are published in a peer-reviewed botanical journal. Generally, this hypothesis is not elevated to the level of a scientific theory. It can be reviewed by another botanist who may accept or reject the species status, perhaps by performing additional tests, such as DNA sequencing. This was essentially the method used by this author in coauthoring a new species of Brodiaea in 2007 named Brodiaea santarosae; however, in our particular case, the hypothesis for a new species came after our preliminary statistical investigation.

    Brodiaea santarosae On The Santa Rosa Plateau Lecture Notes On The Santa Rosa Basalt Brodiaea Article Published In Madrono Vol. 54: 187-198 (2007)  Images of Brodiaeas In Central & Southern California

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    7. Explanations For Moving Rocks Of Racetrack Playa: Theories or Hypotheses?
    

    The sliding (sailing) rocks on Devil's Racetrack move in different directions.

33. The mysterious moving rocks of Racetrack Playa in Death Valley National Park have baffled scientists for decades. Although several plausible explanations have been proposed, no one has actually filmed this remarkable phenomenon in motion or observed it in real time. A few explanations are controversial and not agreed upon by all scientists, and a thorough verifiable and well substantiated proof appears to be lacking. Unfortunately, most references refer to these explanations as theories. As of January 2010 the explanations for this remarkable phenomenon appear to be scientific hypotheses and have not become a comprehensive scientific theory. One thing is certain: The rocks definitely change position with time, and this multidirectional movement has been verified by GPS measurements.
34. Several hypotheses have been proposed to explain the sliding ("sailing") rocks across the lakebed. Most authorities agree with at least two conditions necessary for the movement of rocks. (1) Occasional heavy rains and runoff from nearby slopes producing a slick surface on the fine clays of the lakebed. (2) Gail force, multidirectional winds of at least 80-100 miles per hour, strong enough to push the rocks across the surface in different directions. (3) A third hypothesis builds upon the previous ones and appears to be necessary for larger rocks weighing up to 700 pounds. Freezing nighttime winter temperatures that produce a floating ice sheet on the muddy clay surface. As the lakebed dries, the clay mud shrinks and cracks into a mosaic of interlocking polygons. When the playa fills with water, the fine clay imbibes water and the polygonal cracks coalesce into a sticky surface. Another hypothesis describes colonies of cyanobacteria living in the surface clay that also imbibe water and become mucilaginous, possibly contributing to the slippery surface. Filamentous cyanobacteria secrete a mucilaginous sheath that helps to bind soil particles together in microbial communities known as cryptobiotic crust.

    Cryptobiotic Crust In Anza-Borrego Desert State Park

35. There are additional hypotheses to explain the movement of rocks, however, most of these can be discounted. Gravity can be ruled out since the north end of the lakebed is 1.5 inches (4 cm) higher than the southern end, and most of the rocks traveled slightly uphill. Pranksters during wet years is a possibility, except they left no footprints in the soft, muddy clay surface adjacent to the rocks. Another hypothesis involves aliens from another planet who visited this playa during exceptional wet years.

    More Images Of Racetrack Playa In Death Valley National Monument

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    8. Scientific Theory & Scientific Law

36. As I stated previously, the Working Group on Teaching Evolution, National Academy of Sciences (1998) defines a scientific theory as a well-substantiated explanation of some aspect of the natural world than can incorporate facts, laws, inferences, and tested hypotheses. They define a scientific law as a descriptive generalization about how some aspect of the natural world behaves under stated circumstances. Laws can be very useful in supporting hypotheses and theories, but like all elements of science they can be altered with new information and observations. Scientific theories and scientific laws are both derived from carefully formulated hypotheses that have been scrutinized and repeatedly tested by scientists. In general, they are both accepted to be true by the scientific community and they are both used to make predictions of events. The notion that scientific theories eventually become laws is incorrect. Scientific theories are generally more complex and dynamic than scientific laws; they have many components, and may be changed as the body of available experimental data and analysis develops. In addition, scientific theories explain a whole series of related phenomena. Examples of scientific theories include the chaos theory in mathematics, the theory of relativity in physics, and the theory of plate tectonics and continental drift in geology.

37. Scientific laws are strictly empirical and explain a single action or set of actions. They can sometimes be expressed in terms of a single mathematical equation. Examples of scientific laws include the laws of thermodynamics, Newton's law of gravity, Hook's law of elasticity, Ohm's law, and the gas laws (Boyle's law and Charles' law). Scientific laws may be components of scientific theories. For example, Newton's law of gravity is contained within Einstein's theory of relativity. Mendel's laws of segregation and independent assortment refer to specific mechanisms of the inheritance of genes. They were once hypotheses used by Gregor Mendel in 1865 to explain the inheritance of specific traits in garden peas, such as round vs. wrinkled and yellow vs. green peas. His original hypothesis explained the observed 9:3:3:1 ratios obtained from his dihybrid crosses. Mendel's laws are essential components of the modern theory of evolution; however, there are exceptions to these laws. When Mendel completed his research on genetic crosses with garden peas, he assumed that the individual traits were assorted independently of each other. One of his hypotheses became known as the Law of Independent Assortment. Today we can explain this law because the traits Mendel studied just happened to occur on separate chromosomes. Since the garden pea has 7 pairs of chromosomes, it is obvious that all the hundreds of genes in peas cannot occur independently of each other, and must be located on 7 pairs of homologous chromosomes. Depending on the exact genes you are studying, chromosomal linkage may result in ratios of offspring that are far different from the 9:3:3:1 predicted by Mendel. Laws and theories are the foundations of scientific knowledge; together they explain our complex natural world. They can be modified or changed as more information is available.

    Dihybrid Cross In Corn Similar To Mendel's Crosses With Garden Peas  Smooth vs. Shrunken grains instead of Round vs. Wrinkled peas Purple vs. Yellow grains instead of Yellow vs. Green peas

38. In 1908 English mathematician Godfrey Hardy and German physicist Wilheim Weinberg independently came up with an algebraic expression that describes how genotype frequencies in populations are related to allele frequencies. Known as the Hardy-Weinberg Law, it states that gene frequencies will remain constant generation after generation in large, randomly-mating populations. Although it is a law, it is only applicable under a strict set of conditions, including no mutations, no selection, no migrations between populations (immigration and emigration), and no genetic drift. In a 2-allele system, such as round and wrinkled peas, it is based on the square of a binomial (A + B). In a 3-allele system, such as the A-B-O blood types, it is based on the square of a trinomial (A + B + O). Although it is beyond the scope of this discussion, the Hardy-Weinberg Law is useful for studies in population genetics, particularly the determination of genotype frequencies in populations.
    Percentages Of Blood Genotypes In Hypothetical Population
    There Are 4 Phenotype Percentages Including: 32% Type A (Red),
    15% Type B (Green), 4% Type AB (Blue) and 49% Type O (Brown)

    Alleles	0.2   A	0.1   B	0.7   O
    0.2   A	AA    4%	AB    2%	AO    14%
    0.1   B	AB    2%	BB    1%	BO    7%
    0.7   O	AO    14%	BO    7%	OO    49%

    6 Genotypes In Above Table Appear In The Trinomial Expansion (A + B + O)² =
    A² (4%) + 2AB (4%) + B² (1%) + 2AO (28%) +2BO (14%) + O² (49%)

    See Population Genetics Page

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    9. Evidence For Evolution Based On Fossils & Cladistics

39. A fascinating article about evidence for evolution was written by David Quammen in the November 2004 issue of National Geographic. Evidence for evolution comes from many disciplines, including paleontology, biogeography, anatomy, embryology, physiology, biochemistry and cladistics. Most of Darwin's arguments for evolution in his original Origin of Species (1859) were based almost exclusively on evidence from living organisms (Prothero, 2007). In modern cladistical analysis, computers create elaborate phylogenetic trees or cladograms from DNA sequences containing thousands of base pairs. The cladogram "trees" are organized from the most primitive organisms to the most advanced. The number of shared characteristics between any one species and another indicates how recently these two species have diverged from a shared lineage. Sometimes the cladograms fit the existing models based on fossil evidence and sometimes they do not. Whale paleontologist Peter D. Gingerich collected fossil specimens of early whales from remote areas of Egypt and Pakistan. His research traced the ancestry of whales back to a group of Eocene carnivorous mammals called mesonychids. Evidence from DNA comparisons suggests that whales descended from artiodactyls (even-toed, hooved mammals, such as antelopes, pigs and hippos). Then in 2000, a 47 million-year-old anklebone (astragalus) from a four-legged whale was discovered in Pakistan. This bone closely matched the homologous anklebone in an artiodactyl. The biochemists were right, whales are indeed related to hippos and antelopes!

40. In 2006, a team of scientists, including Edward B. Daeschler, Neil H. Shubin, and Farish A. Jenkins, Jr., unearthed an extinct fossil fish in the Canadian Arctic that dates back to the Devonian Period (360 million years ago). Their discovery appeared in the journal Nature 440 (6 April 2006: 757-763. The fossil fish is named Tiktaalik roseae. This animal has the characteristics of a fish, including gills and scales, but also has the flattened head of a small crocodile and unusual fins used for walking on land. Its fins have thin bones for paddling like most fishes, but they also have sturdy interior bones that would have allowed Tiktaalik to prop itself up in shallow water and use its limbs for support as most four-legged animals do. This remarkable fossil is truly a "missing link," an evolutionary transition between swimming fish and their descendents, a major phylogenetic branch (clade) giving rise to all four-legged vertebrates (tetrapods), including amphibians, dinosaurs, birds, and mammals.

41. Although cladograms are generated from comparative DNA samples, some are produced repeatedly and have higher "bootstrap" values. Cladograms with the highest bootstrap values are considered the most accurate and reliable. For example, if one thousand cladogram "trees" are generated from a comparative DNA sample and the same pattern comes out 900 times, this cladogram would have a bootstrap value of 90 percent. Evolution is a scientific theory because it is based on an abundance of empirical data, even though the precise mechanisms remain open to tests, revision, and tentative acceptance or rejection. There is substantial factual evidence to show that the genetic makeup of populations changes from generation to generation, and that these genetic changes are reflected in a bewildering array of different species of plants and animals.

42. A taxonomic group that represents a single branch (clade) in a cladogram, and having a common ancestor, is termed monophyletic. For example, all birds and reptiles are thought to have descended from a single common ancestor and are monophyletic. DNA evidence also indicates that Humans (Homo) and chimpanzees (Pan) are monophyletic. These phylogenetic studies are not always based on an actual "missing link" which may never be found, or has vanished from the fossil record. Cladograms are typically based on detailed computer analysis of the DNA of extant organisms. Cladograms are also based on fossil evidence, particularly in the field of vertebrate paleontology; however, these are sometimes supplemented with evidence from DNA.

    Definitions Of The Terms Monophyletic, Paraphyletic & Polyphyletic

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43. Duckweeds Now Placed In The Arum Family (Araceae)

    Amorphophallus titanum

    Phylogenetic studies by D.H. Les et al. (2002), G.W. Rothwell et al. (2004) and L.I. Cabrera et al. (2008) indicate that duckweeds belong to the arum family (Araceae). Their cladograms are based on sequences of the trnL-trnF intergenic spacer region of the chloroplast genome. Consequently, the Lemnaceae will no longer appear as a separate family in the latest edition of the Jepson Flora of California. This is especially noteworthy to me since I wrote the section on Lemnaceae for the previous 1993 and 1996 printings! It is interesting to note that duckweeds belong to the same plant family as the titan arum (Amorphophallus titanum). This remarkable plant has a 2.4 m erect spadix that protrudes from a vase-shaped, pleated spathe 4 m in circumference. Many other traditional plant families will also be consolidated as molecular biologists create phylogenetic trees based on consistent monophyletic groupings. Maintaining Lemnaceae and Araceae as distinct families would make the arum family paraphyletic, with a common ancestor but not all of its descendants (i.e. duckweeds are excluded). Modern reptiles is a paraphyletic grouping that contains a common ancestor, but does not contain all descendants of that ancestor (i.e. birds are excluded). Dinosaurs would also be a paraphyletic grouping because it does not contain the bird descendants.

    Cladogram From Cabrera et al. (2008) Placing Duckweeds In Arum Family  Wayne's Word Illustrated Taxonomy Of Duckweed Subfamily (Lemnoideae)

    

    A modern representation of the phylogeny of gymnosperms based on chloroplast DNA. Dichotomous (paired) sister branches (clades) with a common ancestor are said to be monophyletic and are more closely related. For example, the conifer division Pinophyta and ginkgo division (Ginkgophyta) have a common ancestor in the cycad division (Cycadophyta). The pine family (Pinaceae) and a sister branch leading to six additional families have a common ancestor within the division Pinophyta. In other words, the seven major families of cone-bearing trees and shrubs all evolved from the division Pinophyta. The araucaria and podocarpus families (Araucariaceae and Podocarpaceae), which have their greatest diversity in the southern hemisphere, are monophyletic and occur side-by-side on sister clades. Chart by E.M. Armstrong (2008).

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44. The earliest fossils of flowering plants date back approximately 130 million years, to a time when dinosaurs walked the earth. Exactly which ancestral seed plants gave rise to the flowering plants has been a hotly debated topic for more than a century. In fact, in a letter to a friend, Charles Darwin referred to the sudden appearance of flowering plants in the fossil record as "an abominable mystery." Grasses are considered relatively advanced flowering plants, and most macrofossils and pollen from grasses appear long after the demise of dinosaurs at the end of the Cretaceous Period (65 million years ago). Dioramas in museums have long depicted large sauropod dinosaurs grazing on conifers, cycads and ferns in landscapes without grasses. In the November 18 issue of Science, Caroline Strömberg of the Swedish Museum of Natural History and her Indian colleagues Vandana Prasad, Habib Alimohammadian and Ashok Sahni report phytoliths from grasses in the fossilized dung of sauropods that lived in central India about 65 to 71 million years ago.

45. Phytoliths are microscopic silica bodies found inside the cells of stems and leaves of grasses and other plants. Depending on the species of plant, they range from 5 to 100 micrometers in length. Because they are made of a crystalline form of silica called opal, they are very durable and retain their characteristic shapes over millions of years. Like microscopic pollen grains and diatoms, the phytoliths remain perfectly preserved in spaces between soil particles. Different genera of grasses have phytoliths with unique shapes, including square, rectangular, oblong, bilobed, wavy with undulate margins, and butterfly-shaped. Grasses belonging to the subfamily Panicoideae typically have phytoliths that are shaped like a dumb-bell. I examined the leaf blade of crabgrass (Digitaria sanguinalis), a member of the Panicoideae, and the phytoliths are indeed shaped like a dumb-bell.
    

    Magnified view of a row of phytoliths within the leaf epidermis of crabgrass (Digitaria sanguinalis). The dumb-bell shaped phytoliths are 32 micrometers in length. Compare this with an average cuboidal grain of table salt in which each side is 300 micrometers long. More than 800 of these crabgrass phytoliths could fit into a box the size of a grain of table salt! Photo taken at 400x and 1000x magnifications with a light microscope.

46. It is remarkable how much information has been determined about the distant geologic past with new and improved methods of chemical analysis and sophisticated digital instruments. Each day the scientific theory of evolution is becoming more complete, as scientists uncover new facts and piece them together like a complex jigsaw puzzle. DNA, the genetic blueprint of all creatures, provides a stunning, detailed record of evolution, from primitive unicellular bacteria to complex vertebrate animals. This is eloquently described by Sean B. Carroll in his book The Making of the Fittest (2006).

    Phytoliths & Dinosaur Coprolites   Grains of Salt & Metric System A Comparison Of Cell Sizes

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    silver sword

    10. Adaptive Radiation On The         Hawaiian Archipelago

    alula

47. The Hawaiian archipelago has been isolated from continental land masses during the past 30 million years, and yet the 1,000 species of indigenous Hawaiian angiosperms are believed to stem from natural introduction by long-distance dispersal of 280 ancestral plant colonists (Manual of the Flowering Plants of Hawaii by Wagner, W.L., Herbst, D.R. and S.H. Sohmer, 1990). It appears that seeds were carried thousands of miles to these islands, possibly by rafting or within protective capsules and pods. For example, an ancestral California tarweed of the sunflower family (Asteraceae) traveled at least 3,000 miles to the Hawaiian Islands where it gave rise to a remarkable group of endemics known as the "Silver Sword Alliance." The small seeds from ancestral members of the lobelia family (Campanulaceae) also reached these islands from the American mainland giving rise to an unusual group of endemic Hawaiian lobelioids. This phenomenon where ancestral species colonize a new habitat and evolve into different species is called adaptive radiation. The new species evolve in response to different selection pressures that enable them to fill unique ecological niches. The story of Darwin's Finches on the Galapagos Islands is a classic example of adaptive radiation. The Hawaiian silver swords and lobelioids are truly unusual in appearance. They are strikingly different in appearance compared with California tarweeds or members of the lobelia family on the mainland of North and South America. Their taxonomic affinities with ancestral species are based on chromosome comparisons, hybridization studies and comparative chloroplast DNA. The unscientific hypothesis that these bizarre plants were placed here in their present form by a creator is untenable.
    

    Alula (Brighamia insignis), a rare member of the lobelia family (Campanulaceae) endemic to steep sea cliffs on the island of Kauai. Alula is perfectly adapted for living on vertical volcanic cliffs. A single rosette of leaves arises from the top of a thick, succulent stem, like a cabbage head on a baseball bat. The rosette varies in size, depending on the availability of moisture. Roots penetrate the cliffs horizontally, and the base of the plant is rounded, permitting the plant to rock slightly in the wind. Water stored in the stem enables the plant to survive periods of drought which may last days or weeks. The flower is very different from members of the lobelia family on the mainland of North America. Another rare species with white flowers (B. rockii) grows on sea cliffs along the windward coast of Molokai. Like Hawaii's endemic silver sword alliance that evolved from an ancestral tarweed (Asteraceae), the alulu is another example of adaptive radiation. According to Sherwin Carlquist (Hawaii: A Natural History, 1980), the Hawaiian lobeliads evolved from several ancestral introductions rather than a single original colonization; however, molecular data from Thomas J. Givnish of the University of Wisconsin (Evolution on Islands, 1998) indicate that they are monophyletic in origin and represent the product of a single introduction.

    The Silver Sword Alliance

    Lobelia Family In California: Scarlet Lobelia: Lobelia cardinalis Vernal Pool Downingia: Downingia bella  Vernal Pool Downingia: Downingia cuspidata

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    11. Homoplasy: Parallel & Convergent Evolution
    

    A small mantispid and a preying mantis. Although they differ greatly in size, these two insects are remarkably similar in appearance. They both have triangular heads with large eyes and a pair of raptorial (grasping) front legs. Their other two pairs of legs are used for walking. They belong to two very different insect orders. Although mantids were once placed in the order Orthoptera along with grasshoppers, crickets and cockroaches, they are now placed in the separate order Mantodea. Mantispids belong to the order Neuroptera, along with lacewings, snakeflies and antlions. Their remarkable adaptive similarity is an example of convergent evolution.

48. Sometimes evolutionary change follows a common pathway in two or more unrelated or distantly-related organisms because of similar environmental pressures. It culminates in unrelated organisms with similar morphological characteristics even though they did not have a common ancestor. This phenomenon is called parallel evolution. There are many examples of parallel evolution in plants, including distantly-related plant families that have evolved from an autotrophic to a parasitic mode of existence. Some plants have evolved independently into a mycotrophic mode of existence where they obtain nutrients from mycorrhizal soil fungi, which in turn, are parasitic on the roots of nearby forest trees and shrubs. Photosynthetic pathways, such as CAM (crassulacean acid metabolism) and C-4 photosynthesis, have also evolved independently in distantly-related plant families. When parallel evolution results in organisms that greatly resemble each other in overall appearance and possess similar adaptations, this is called convergent evolution. It should be noted here that some authors use these two terms interchangeably.

    C-4 Photosynthesis CAM Photosynthesis Parasitic Flowering Plants  Mycotrophic Flowering Plants

49. Another hypothetical example of parallel evolution is the appearance of xylem vessels in the vascular tissues of very distantly-related plants, such as Ephedra in the gymnospermous division Gnetophyta and flowering plants in the angiospermous division Anthophyta (Magnoliophyta). In addition, species of Ephedra have double fertilization, where two sperm are involved in the fertilization process. Double fertilization was once thought to be a strictly angiosperm characteristic. Some older references have suggested that the Gnetophyta may represent a "missing link" in the evolution of flowering plants, but others say that vessels and double fertilization are examples of parallel evolution. Considering all their amazing similarities, it seems quite plausible that the Gnetophyta and angiosperms may have shared a common ancestor. If the latter hypothesis is correct, then the appearance of vessels and double fertilization in these two groups of vascular plants would not be parallel evolution. In fact, modern cladograms indicate that the divisions Gnetophyta and Anthophyta (Magnoliophyta) are monophyletic and share a common ancestor.
    

    Left: Ephedra viridis in the Panamint Range overlooking Death Valley National Monument. Right: Wildflowers in Anza-Borrego Desert State Park. Although Ephedra belongs to an entirely different plant division (Gnetophyta), it has several characteristics of flowering plants (division Anthophyta) including vessels and double fertilization. These traits are considered to be homoplastic because they evolved independently through parallel evolution. Convergent evolution would not be used here because Ephedra and flowering plants appear very different from each other. If Ephedra and flowering plants shared a common ancestor, the appearance of these traits would not be an example of parallel evolution. [Wildflowers include Encelia farinosa, Cylindropuntia bigelovii, Lupinus arizonicus and Mimulus bigelovii.]

    The Remarkable Gymnosperms: Ephedra & Welwitschia   Stem & Root Anatomy Of Angiosperms & Gymnosperms

50. The laurel family (Lauraceae) includes about 2,000 species of trees and shrubs in 50 genera. Familiar genera in the family include Cinnamomum (cinnamon and camphor), Laurus (European bay), Umbellularia (California bay), Sassafras and Persea (avocado). One genus in this family (Cassytha) has broken away from the other trees and shrubs and has evolved into a leafless, twining parasitic herb that absorbs nutrients from it host by a specialized modified root called a haustorium. The distantly-unrelated morning-glory family (Convolvulaceae) also has about 50 genera of trees, shrubs and vines. Like the laurel family, one of these genera (Cuscuta) has evolved into a twining, leafless parasitic herb with a specialized organ of absorption (haustorium). Some botanists place this genus in its own family, the Cuscutaceae, although the floral morphology is very similar to some members of the Convolvulaceae. Both Cassytha and Cuscuta are remarkably similar in appearance, even though they live in different parts of the world and do not share a common ancestor. The radical modification of these two unrelated plants into specialized parasites is a marvelous example of convergent evolution.
    

    Left: Cassytha filiformis (Lauraceae) on the Caribbean Island of Grand Cayman. Right: Cuscuta californica (Convolvulaceae or Cuscutaceae). These twining, parasitic plants are without chlorophyll and absorb nutrients from their host plants be means of specialized roots called haustoria.

51. The distinction between parallel and convergent evolution is not always that clear, and some authors use these two terms interchangeably. When parallel evolution under similar environmental conditions in unrelated or very distantly-related organisms results in plants and animals that are morphologically very similar in overall appearance, this is called convergent evolution. The independent evolution in these organisms has proceeded in remarkably the same manner, and the products are practically indistinguishable to the casual observer. North American cactuses (family Cactaceae) and South African euphorbias (family Euphorbiaceae) belong to different plant families and are distant relatives in the phylogeny of flowering plants; however, they both have succulent, thick stems that store water, they both have spines for protection, and they both are adapted for survival in arid desert regions with low rainfall. Without flowers, some African euphorbias are practically indistinguishable from their North American counterparts.
    

    Homoplasy: Which of these xerophytes is a cactus and which one is a euphorbia?

    The Diverse Euphorbia Family

52. In Australia there are many examples of marsupials that resemble our North American placental mammals. For example, Australia's flying phalanger is remarkably similar to the North American flying squirrel. Both tree-dwelling mammals glide through the air with their parachute-like fold of furry skin between the front and hind legs. These are excellent examples of convergent evolution.

53. The supplemental biology text Of Pandas and People (2nd. Edition, 2004) that is endorsed by advocates of intelligent design includes a different definition for parallel evolution. According to the authors of the latter text, "If two organisms are judged to be related through a "recent" common ancestor, their similarities are said to result from parallel evolution." They also state that if the ancestor is distantly related, convergent evolution has occurred. This definition of parallel evolution is incorrect. If two organisms are derived from a common ancestor, then the terms parallel and convergent evolution are not applicable.

54. The terms homology and homoplasy may be easier to understand. Homology refers to similarity due to a common ancestor. Characteristics derived from a common ancestor are termed homologous. Homologous organs are similar in structure and embryonic origin but are not necessarily similar in function. Cactus spines are homologous to bud scales of an axillary bud. Seed-bearing carpels of flowering plants are homologous to leaves because of their similarity in form, anatomy and development. Homoplasy (ho-MOP-la-see) means similarity due to independent origin that is not from a common ancestor. Homoplastic characteristics, such as the spines of cacti and stem-succulent euphorbias, evolved independently from each other. Cactus spines arise from an axillary growth center called an areole. Euphorbia spines are derived from modified stipules. Homoplasy includes parallel and convergent evolution. Similarity of structure in unrelated or distantly-related organisms is often the result of similar evolutionary pathways under similar environmental conditions. Using the term homoplasy avoids the confusing distinction between parallel and convergent evolution.
    

    A. Equisetum (Division Sphenophyta). B. Casuarina (Division Anthophyta). Two unrelated plants in different divisions of the plant kingdom. They both have jointed stems with whorls of scale-like leaves at the nodes. One is a flowering tree and the other is a non-flowering plant with an apical spore-bearing cone (strobilus). Is this an example of homology or homoplasy?

    See Modified Leaves & Stems

55. The recently discovered cerambycid beetle Onychocerus albitarsis in Peru is truly one of the most remarkable examples of convergent evolution (homoplasy). It is described by A. Berkov, N. Rodriguez and P. Centeno in Naturwissenschaften Vol. 95, March 2008. Venom-injecting structures have arisen independently in unrelated arthropods, including spiders, centipedes and antlions. The venom is injected through hollow fangs (poison jaws), or in the case of centipedes, through modified forelegs. Among insects only wasps, bees and ants of the order Hymenoptera are known to possess true stingers. Microscopic examination of the newly discovered beetle has revealed that the tip of each antenna is truly a stinging device. In fact, Mr. Centeno discovered this fact first hand. As he grabbed the beetle, the insect jerked back its antennae and pricked his finger, which swelled as if stung by a bee. This is the first example of a stinger in the enormous beetle order Coleoptera.

56. The terminal antennal segment of Onychocerus albitarsis has two pores opening into channels leading to the pointed tip through which the venom is delivered. The delivery system is almost identical to that found in the stinger of certain scorpions. Since beetles and scorpions belong to entirely different arthropod orders and are only distantly related, this is a dramatic example of homoplasy: similarity due to independent origin that is not from a common ancestor. In this case the homoplastic characteristics (stinging devices) evolved independently from each other. Although the article in Naturwissenschaften uses the term "convergent evolution," one might argue that this is "parallel evolution." The term homoplasy makes this confusing distinction unnecessary.

    Tail of Arizona desert scorpion (Hadrurus arizonensis)

    Beetles, Stinging Organs, and Fang-Like Jaws The Diverse Order Of Beetles The Stinging Tail Of Scorpions The Fang-like Jaws Of Antlions The Fangs Of A Jumping Spider   Fang-like Forelegs Of Centipedes

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    Origin Of Eyes In Distantly Related Animals. Is This An Example of Homoplasy?

57. In Chapter 6 of The Origin of Species, Charles Darwin expressed concern over how a complex organ, such as the eye, could evolve by natural selection. "... if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if any variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, can hardly be considered real." In fact, some creationists have taken the previous quotation out of context and used it in their argument against evolution be means of natural selection. Like the wings of birds, bats and insects, many biologists have used the term homoplasy to explain the independent origin of eyes in diverse groups of animals. In fact, because the anatomy of the camera-like vertebrate eye is so different from the simple eyes of limpets and the compound eyes of insects, scientists thought that eyes evolved independently numerous times.

58. Homoplasy may not adequately explain the origin of eyes in different animal phyla. Recent evidence indicates that eye-forming genes evolved only once in a distant ancestor. These primordial eye genes provided the ancestor of present-day animals with photoreceptor cells and the ability to detect light. Mutations and evolution brought other genes under the control of these primordial genes, and together they produced a variety of eyes from simple to complex. With photoreceptor cells at the base of a simple eye cavity, mutations and modifications leading to a more advanced eye are plausible. An explanation for the development of eyes in different present-day species of mollusks is presented by M.F. Land and D.-E. Nilsson (2002) in their book Animal Eyes. This fascinating hypothesis is summarized by C. Zimmer in the November 2006 National Geographic.
    

    Three examples of mollusks in the diverse phylum Mollusca.

59. All of the following mollusks share a common ancestral trait: A layer of light-sensitive cells at the base of an eye cavity. In the limpet, this layer of photosensitive cells in a shallow depression can detect light but the eye cannot produce an image. Beyrich's slit shell has a deeper eyecup that provides more information about the direction of the light source, but creates no image. In the chambered nautilis, a small gap at the top of the eye cavity acts as a pinhole pupil, focusing light on photosensitive cells that serve as a rudimentary retina. In Murex, fluid in a fully enclosed eye cavity functions as a primitive lens, focusing light on the retina to create a slightly sharper image. In the common octopus, advanced vision is created by a more complex eye equipped with a protective cornea, colored iris, and focusing lens.

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    12. Punctuated Equilibrium & Symbiogenesis

60. The term evolution is very broad and has numerous subdivisions, particularly explanations for the mechanisms of change. Charles Darwin's "On the Origin of Species by Means of Natural Selection" was a testable scientific hypothesis that explained one mechanism of evolution called natural selection. Alfred R. Wallace also came up with this hypothesis at the same time period (see "The Man Who Wasn't Darwin" by David Quammen in December 2008 National Geographic). In fact, Darwin and Wallace coauthored a paper on natural selection for Journal of the Proceedings of the Linnean Society in 1858. The following year, Darwin published his Origin of Species and his name is usually associated with the theory of evolution. Natural selection may explain some aspects of evolution; however, there are other explanations. In the first edition of Origin of Species, Darwin was careful to acknowledge the limits of natural selection, writing, "I am convinced that natural selection has been the main but not the exclusive means of modification." Nevertheless, he was misinterpreted as claiming that natural selection was entirely responsible for evolution. In fact, evolution and natural selection have been used interchangeably by some authors. Other scientific hypotheses to explain certain mechanisms of evolution include punctuated equilibrium and symbiogenesis. Punctuated equilibrium was proposed by Niles Eldredge and Steven Jay Gould in the 1970s. It postulates that speciation may occur relatively quickly in geologic time, with long periods of little change (equilibria) in between. Punctuated equilibrium explains the evolutionary patterns of species as observed in the fossil record, particularly the sudden appearance of new species in a geologically short period of time.

61. Another scientific hypothesis known as symbiogenesis, is described in the book entitled Acquiring Genomes: A Theory of the Origins of Species by L. Margulis and D. Sagan (2002). According to the authors, genomic mergers are a major source of genetic variability leading to the evolution of species. Instead of relying on the hit-or-miss method of random mutations, symbiogenesis provides advantageous genetic combinations through the fusion of entire genomes from two or more organisms. This phenomenon may have been a major factor in the evolution of land plants from lichen-like ancestors. In 1981, Lynn Margulis also proposed the endosymbiont hypothesis to explain the origin of organelles within eukaryotic cells. According to endosymbiosis, cellular organelles (mitochondria and chloroplasts) originated from bacteria and cyanobacteria that became incorporated within living cells. When these original hypotheses have been repeatedly tested and scrutinized by different scientists, they may become scientific theories.

62. The arise of photosynthetic organelles called chloroplasts represented a major step in the evolution and diversification of plant life on earth. This event had a significant effect on the evolution of animal life that depended on the plants for food, either directly in the case of herbivores, or indirectly in the case of carnivores. Chloroplasts exhibit remarkable similarities with cells of cyanobacteria, and may have shared a common prokaryotic ancestry. Indeed, the outer membrane structure and circular DNA molecules of chloroplasts and mitochondria are very similar to individual prokaroytic cells. According to the endosymbiont hypothesis (or endosymbiont theory for those who are less skeptical), ancient photosynthetic prokaryotic cells became incorporated within the cells of algae or ancestral plants, forming stable mutualistic symbionts known as chloroplasts. Mitochondria may have had a similar origin. Without chloroplasts and oxygen-producing photosynthesis, the amazing diversity of today's plants and animals may have never evolved.

63. According to Margulis and Sagan (2002), there is even a green photosynthetic animal named Elysia viridis, a minute slug (saccoglossan opisthobranch) that never feeds throughout its adult life. Instead, it obtains carbohydrate-rich molecules by bathing in the sunlight. This slug evolved from algae-eating ancestors, only the algal cells entered the slug's tissue and remained their as photobionts (photosynthetic symbionts). According to some invertebrate zoology textbooks, the chloroplasts from algae cells are sucked into the slug's gut and incorporated within digestive gland cells where photosynthesis occurs.

64. There are numerous examples of plants and animals that contain microbial symbionts within their tissues, including bacteria, cyanobacteria, protozoans and algal cells. Cycads, water ferns (Azolla), legumes and the tropical flowering plant Gunnera contain nitrogen-fixing bacteria in their tissues; sea anemones and corals contain photosynthetic unicellular algae (zooanthellae and zoochlorellae); the rumen of cattle contain cellulose-digesting bacteria; termite guts contain flagellated protists which contain wood-digesting bacteria; and human intestines contain bacteria that produce essential B vitamins.
    

    The water fern Azolla filiculoides contains colonies of filamentous cyanobacteria (Anabaena azollae) within cavities in its leaves. [See magnified inset.] These two organisms once formed an intimate symbiotic marriage many millions of years ago and have remained together ever since. Azolla provides a protected place for the Anabaena to survive at the surface of ponds and streams in full sunlight. Like other nitrogen-fixing organisms, colonies of Anabaena convert inert atmospheric nitrogen into ammonia, a form of nitrogen that is available to Azolla and other plants. Nitrogen-fixation occurs in oval cells called heterocysts (red arrow).

65. Lichens are one of the best examples of symbiogenesis involving the fusion of algal and fungal genomes (kingdoms Protista and Fungi). Some lichens include the genome of a third kingdom Monera because they contain prokaryotic cells of cyanobacteria. In the case of lichens, this genomic merger has enabled these organisms to survive in some of the most inhospitable environments on earth, where neither symbiont could survive on its own. In fact, lichens are an excellent example of synergism because the whole is truly greater than the sum of its parts. The algal and fungal components develop into a unique body form with morphological features quite different from either symbiont.
    

    Center: British soldiers (Cladonia cristatella), a soil lichen with upright stalks (podetia) bearing bright red apothecia at the tips. At the bottom of the centrifuge tube (A), the fungal component of this lichen (also named C. cristatella) has grown into a white, amorphous blob without its algal symbiont. In the right test tube (B), the algal symbiont (Trebouxia erici) has grown into a mass of bright green cells. Only when the genomes of the two symbionts form the "marriage" known as lichen is the unique structure of "British soldiers" formed. In true synergistic fashion, this lichen is truly more than the sum of its parts. For example, the podetium is a unique lichen structure that is not found in the algae or fungi.

    Symbiogenesis & The Endosymbiont Hypothesis  The Marriage Between Azolla & Anabaena Prokaryotic Cells & Nitrogen Fixation

66. Both Darwin and Wallace are credited with the scientific hypothesis of evolution by means of natural selection. This hypothesis has been tested repeatedly by scientists during the past century and it is now elevated to the status of a scientific theory. Our knowledge of the evolution of life on this planet has grown considerably during the past 147 years since the time of Darwin. In fact, the term "Darwinist" repeatedly used in the intelligent design textbook Of Pandas and People is misleading. Does Darwinist refer to one who believes in the teachings of Darwin, or one that follows the modern scientific theory of evolution that encompasses many new concepts since the time of Darwin? The latter interpretation of evolution includes substantial information from the fields of genetics and molecular biology and is often referred to as neoDarwinism.

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    13. Coevolution Between The Fig & Its Wasp: Vicarious Selection A Complex and Remarkable Life Cycle That Defies Oversimplifications and Generalizations

67. One of the most remarkable examples of coevolution between a plant and an insect is the fig tree and its symbiotic wasp. Minute male and female fig wasps are borne inside hollow, fleshy, flower-bearing structures called syconia. [The syconium is what most people associate with the tasty fruit of a fig, but technically it is not a true fruit.] The syconium is lined on the inside with hundreds of tiny, apetalous, pollen-bearing male flowers, long-style, seed-bearing female flowers, and short-style female flowers. Fig wasps develop from eggs laid inside the ovaries of the short-style female flowers (one egg per flower). In about half of the fig species (referred to as monoecious), male flowers and the long and short-style female flowers occur in the same bisexual syconium; but in all other fig species (referred to as dioecious or gynodioecious), the seed-producing, long-style female flowers only occur in unisexual syconia on female trees, while pollen-bearing male flowers and wasp-bearing, short-style female flowers occur in the same syconia on male trees. In the common edible fig (Ficus carica) the male trees are called caprifigs. [The prefix capri refers to goat, and these figs were apparently fed to goats.] Wasp eggs are not laid in the ovaries of long-style flowers because the wasp's ovipositor cannot reach the ovary; therefore, the ovary develops a seed rather than a wasp (assuming it is pollinated). Without the symbiotic wasps transferring pollen from one syconium to another, the female flowers inside would not get pollinated and no seeds would be produced (a catastrophe for the fig tree). This remarkable floral dimorphism (heterostyly) is how the fig tree produces seeds (on female trees) while still maintaining its vital, "in-house" population of symbiotic wasps on male trees. There are approximately 1,000 species of figs (genus Ficus), mostly distributed throughout tropical regions of the world, and they all have one or more pollinator wasps that enter their syconia through a small opening (called an ostiole) to pollinate the female flowers inside. Depending on the fig species, pollen is transferred to the female flowers, either passively or purposively. In the latter case the wasp actually transfers pollen from pollen baskets (corbiculae) on the underside of her thorax to the stigma.
    

    Life cycle of the common fig (Ficus carica). Style length is genetically determined and it is vital that syconia on seed-bearing female trees have styles longer than the female wasp's ovipositor. Unable to reach the ovaries of these flowers, she does not lay eggs (oviposit). Therefore, a seed develops inside the ovary rather than a wasp larva. She can only oviposit in the short-style female flowers on "male" trees called caprifigs. Caprifig trees produce pollen and the crucial pollinator wasps (Blastophaga psenes). In some common figs termed "caducous" or early deciduous, the immature female syconium drops from the tree if the flowers inside are not pollinated. There are many cultivated "parthenocarpic" varities of the common fig in which the syconia develop on female trees wthout wasp pollination (caprification). The ripe syconia are fleshy and edible; however, the numerous ovaries (drupelets) inside are hollow and seedless.

68. In short-style female flowers, the wasp inserts her ovipositor down the stylar canal and lays an egg in the ovary of the flower. The subsequent larva feeds on endosperm tissue initiated by the ovipositing pollinator wasp. Since the endosperm in some figs may be initiated parthenogenetically (without pollination and fertilization), possibly by a mechanical or chemical stimulus during oviposition, food tissue for the developing larva functions like a minute gall. Style length is genetically controlled, and it is important for the tree to have style lengths longer than the wasp's ovipositor in long-style flowers so that seeds can develop in these ovaries. It is also important to have flowers with short styles so that female wasps can lay eggs (oviposit) in the ovaries. "Bogus" fig wasps (parasitoids and inquilines) with extra long ovipositors present a formidable problem to figs. They can readily lay eggs in long-style flowers, and can even penetrate the syconium wall without pollinating the female flowers inside. Some dioecious figs can counter this problem by simply aborting unpollinated syconia, thus ridding itself of seedless syconia. This strategy does not work on monoecious figs with multiple style lengths in the same syconium. Dioecious figs may represent an advanced (further evolved) species.

    Overwintering mame crop of syconia.

    A fig wasp larva inside the ovary of a short-style female flower in an overwintering mamme syconium. This is the leafless dormant season for the caprifig (Ficus carica). Since the previous mammoni crop of syconia do not produce pollen, the larva fed on parthenogenetic endosperm tissue that developed without pollination. The initiation of endosperm tissue after oviposition by the female wasp meets the criterion for gall formation. The larva consumes the galled tissue within the ovary wall. After metamorphosis, the adult male wasp chews a hole through the ovary wall and exits the female flower. He crawls to another short-style female flower that contains a mature female wasp. He climbs up on the ovary of the flower, bites a fertilization hole in the ovary wall, and inserts his long, slender abdomen into the opening, thus inseminating the female. After being inseminated, the female crawls out of the fertilization hole through the ovary wall initially made by the male. Wasp larva photographed in January 2009.

    The Calimyrna Fig & Its Pollinator Wasp   The Remarkable Fig/Fig Wasp Scenario Sex Determination Of The Common Fig Do Fig Wasps Really Produce A Gall? All Fig & Fig Wasp Symbiosis Pages

69. It should be noted here that some fig species have two or more species of symbiotic wasp pollinators. In fact, the classic one-fig/one-wasp partnership has been challenged by D. Molbo, et al. (Proceedings of the National Academy of Sciences 100, 2003). S. G. Compton, et al. (African Entomology, 2009) found three or more species of pollinator agaonid wasps in the syconia of Ficus natalensis. Fig wasp species may be closely related sister taxa, or may be quite different from each other. This indicates both long-term coexistence on shared hosts and relatively recent colonization of fig species. Fig syconia may also contain wasps who do not pollinate the female flowers inside. It is clear that the fig/fig wasp scenario is far more complicated than originally described. In fact, Richard Dawkins (personal communication, 1996) agrees that it is a difficult subject to adequately cover in laymen publications about evolution. There are literally thousands of articles on this subject with numerous exceptions and contradictions to any universal fig wasp life cycle pattern.
    

    A. Close-up view of a male and female fig wasp (Pleistodontes imperialis) that inhabits the syconia of the Australian rustyleaf fig (Ficus rubiginosa). The slender ovipositor on female wasp is too short to penetrate the ovary of long-style flowers; therefore she does not lay eggs in these flowers. The smaller, wingless male has large mandibles and a greatly reduced body which has two primary purposes: (1) Inseminating the female and (2) Chewing exit tunnels through the syconium wall through which the females escape. The "eye" of an ordinary sewing needle is shown for a size comparison. B. A non-pollinator "bogus" fig wasp collected from the syconium of the Baja California wild fig (Ficus palmeri or possibly Ficus brandegeei). The ovipositor is much longer than the symbiotic pollinator wasp. In fact, some non-pollinator wasps can penetrate the entire syconium wall from the outside. They can also lay eggs in long-style fig flowers reserved for fig seeds. Consequently, no seeds are produced in these flowers. In addition, these "bogus" fig wasps do not pollinate fig flowers. Although they do not benefit the fig tree, non-pollinator wasps of the families Torymidae and Eurytomidae are common inhabitants of New World monoecious fig syconia. Their coexistence with natural fig pollinator wasps is a complex and perplexing coevolutionary problem in fig biology.

    Size Of Sewing Needle In Wayne's Word Images  Ficus palmeri In Mtns & Coastal Baja California

70. According to Carole Kerdelhue and Jean-Yves Rasplus (Oikos Vol. 77, 1996), dioecious figs may have evolved from monoecious ancestral fig species due to selection pressure by non-pollinating fig wasps. Although these non-pollinator wasps belong to the same order Chalcidoidea as pollinators, many of them belong to different families. They do not benefit the fig and may even be harmful, especially when they compete with and/or parasitize the beneficial pollinator wasps. The non-pollinator, parasitic wasps never occur in the long-style flowers of syconia on female trees, and non-pollinator wasps are uncommon in the syconia of male trees. Therefore, seed production in syconia on female trees and pollinator wasp production in syconia on male trees are not diminished, as in the syconia of monoecious figs containing detrimental non-pollinator wasps. Kerdelhue and Rasplus, 1996) state that no gall-makers that lay eggs through the syconium wall (after pollination by beneficial pollinator wasps) have ever been found so far in dioecious figs; however, agaonid wasps of the genus Philotrypesis that oviposit through the syconium wall are well known in the dioecious edible fig (Ficus carica). In general, having separate male and female trees in the population may be an adaptive advantage with regards to pollination and seed production.
    

    Left: A dioecious fig showing short-style and long-style female flowers inside syconia of male and female trees. Non-pollinator wasps typically do not inhabit these syconia. Right: The monoecious syconium of the South African Ficus sur contains long-style and short-style female flowers densely packed together in a layer that lines the inner cavity of the syconium. Although the styles all form a relatively continuous stigmatic layer called a synstigma (i.e. all stigmas in the same plane) within the syconium, the ovaries may be deep or shallow relative to the synstigma depending on the length of their flower stalks (pedicels). There are four style lengths (heterostyly) and four ovary positions designated by different colored ovaries. Generally, the deep-seated black ovaries (on short pedicels) with long styles each contain a seed, while the shallow yellow ovaries (on long pedicels) with short styles each contain a wasp larva. A pollinator wasp walking on this "bed" of styles (synstigma) can insert her ovipositor down the short style and easily penetrate the ovary where she lays an egg. The deep-seated, long-style ovaries are out of reach for her ovipositor (style longer than her ovipositor), and consequently these ovaries develop seeds rather than wasp larvae. If the non-pollinating wasps are very numerous, the medium layers 1 and 2 (yellow and green ovaries) will be occupied entirely by exploiters and these occupied flowers will not produce seeds or pollinator wasps. According to Kerdelhue and Rasplus (1996), this probably represents a high cost to the fig with regard to seed production. The above syconium structure is not the case for all monoecious figs. According to Zhang, et al. (Annals of the Entomological Society of America Vol. 102, 2009), the Asian fig F. curtipes and relatives (subgenus Urostigma, subsection Conosycea) lack a synstigma, which is replaced by an irregular mass of elongate stigmas. The stigmas are unbranched, slightly curved, and only slightly broader than the style. Instead of walking on a mat of stigma tips (synstigma), the female wasps frequently stumble and fall between different stigmas as they attempt to find oviposition sites. The lack of a fused synstigma enables the wasps to insert their ovipositors at the basal end of the stigmas, not at the top of stigma as described in other species, which reduces the length of ovipositor that has to be inserted. Thus, the ovipositor of the pollinator Eupristina sp. is sufficiently long enough to reach all the ovules. In other figs with unbranched stigmas (subgenus Sycomorus) and figs with branched stigmas (subgenera Urostigma and Pharmacoscea), oviposition occurs at the top of stigma. Oviposition behavior in fig wasps is therefore not universal, and is responsive to variation in floral structure within their host figs. There may indeed be factors other than style length preventing oviposition in long-style flowers.

    Vicarious Selection

    Plausible explanation for why pollinator wasps don't evolve longer ovipositors so they can oviposit in the long-style female flowers.

71. In his book "Climbing Mount Improbable (1996), Richard Dawkins devotes Chapter 10 to the fig/fig wasp coevolution and the model for vicarious selection proposed by Grafen and Godfray (Proceedings of the Royal Society, 1991). In vicarious selection of the dioecious fig subgenus Urostigma, morphology (style and ovipositor length), and wasp behavior (purposive loading and unloading of pollen) is taking place in wasps who enter and leave male syconia containing short-style female flowers on male trees. This selection is crucial for the perpetuation of fig trees when wasps enter female syconia on female trees (which superficially resemble male syconia). Female syconia produce seeds (the vital genetic link for fig trees) and are a genetic graveyard for wasps because they cannot oviposit in the long-style female flowers. The female wasps die in these syconia. For wasps in female syconia, mutations for a longer ovipositor that could reach the ovary of long-style flowers would not be passed on. For wasps in male syconia, there is no selective advantage for longer ovipositors because they are perfectly adapted for laying eggs in the ovaries of short-style flowers. Vicarious selection does not explain the evolution of ovipositor length in all figs, particularly the numerouas monoecious species. The fig/fig wasp scenario is much more complicated, with many variations in the life cycles depending on the different subgenera. Unfortunately, it is beyond the scope of this essay.

    Key To Subgroups Of Dioecious (Gynodioecious) Figs

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    14. Natural Selection & Survival of the Fittest

72. There are many remarkable examples of natural selection in animals where a particular adaptation has survival value. Some of these include camouflage (protective form & coloration), warning coloration and mimicry. The main evolutionary advantage for these adaptations is to avoid being eaten by predators long enough to pass on your genes to future generations, thus perpetuating the species. Consider Batesian mimicry in a harmless little snake with a banding pattern similar to a deadly Arizona coral snake (Micruroides euryxanthus). A predator might not attack this snake because of its coloration. Similar banding patterns among different species of poisonous coral snakes is termed Mullerian mimicry.
    

    Only one of these snakes has the banding pattern of a deadly Arizona coral snake (Micruroides euryxanthus). Helpful rhyme: "Red bordered by yellow, kills a fellow." If you guessed correctly on the banding pattern of the poisonous species, please do not feel overconfident in identifying all coral snakes and their mimics. The classic rhyme does not apply to the poisonous coral snake (Micrurus frontalis) native to Brazil.

    

    A striking South American lanternfly (Phosphora lanternaria). The enlarged head extension mimics the head of a small alligator. Some authorities have suggested that the reptilian head may ward off an attack by potential predators of this harmless, plant-eating insect. It has also been suggested that the head resembles an unshelled peanut; however, it is doubtful that any adaptive advantage can be gained by mimicking a peanut. These mimics are the derivation of the common names "gator" lanternfly and "peanut" lanternfly.

    

    Leafy sea dragon (Phycodurus eques), one of the most remarkable examples of camouflage in the animal kingdom. Native to southern Australia, this fish is difficult to distinguish from leafy seaweeds. In fact, at first glance it is hard to tell that it is a fish. Sea dragons belong to the order Solenichthyes, along with sea horses and pipefish.

    Additional Sea Dragon Images Plant & Animal Adaptation Links  Plant & Animal Adaptation Images

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    15. Faith & The Existence Of Coconut Pearls

73. An example of a common theory based on faith is the existence of coconut pearls, beautiful calcareous stones that allegedly form inside coconuts. Most records of coconut pearls are second-hand accounts where the owner never actually saw the pearl within its original coconut. Published first-hand accounts have been shown to be fraudulent. All tested coconut pearls have been shown to be pearls and polished shells from giant clams (Tridacna) of Malaysia. They were carefully inserted into coconuts to fool the owners, or simply came with fictitious stories about their origin. In fact, I almost purchased one from Singapore until I discovered its price of $60,000 U.S. dollars! Although millions of coconuts are harvested annually, there is no documented coconut pearl that has survived scientific analysis by authorities. Without empirical evidence, the existence of coconut pearls appears to be a myth (Armstrong, 2005 & 2007). Completely independent of my research, Dr. J.V. Veldkamp of the National Herbarium of the Netherlands and editor of the prestigious journal Flora Malesiana Bulletin, has also been studying coconut pearls called "mestica calappa" and published a paper on this subject for Flora Malesiana Bulletin in 2002. Like myself, he is now convinced that they are a hoax and is updating his original article in the next issue of Flora Malesiana Bulletin.

74. Some authors still maintain that coconut pearls exist and continue to perpetuate this assumption in the literature. They say: "Just because there is no proof of their existence, does this mean that coconut pearls do not exist?" A scientist would say: "With the complete lack of proof for the existence of coconut pearls, the probability of finding one inside a coconut is extremely unlikely, and their existence appears to be based on faith rather than objective facts." There are websites where you can actually purchase "coconut pearls." One site claims that the authenticity of their "coconut pearls" is based on psychic verification by a trained shaman. They also state that they cannot guarantee the authenticity of their "coconut pearls" with 100 percent certainty, but this "does not mean the pearls and stones are fake." I suppose it isn't too surprising to see "coconut pearls" for sale on the Internet since there are also websites offering extraterrestrial real estate for sale on the moon.

    See Disclaimer On The Existence Of Coconut Pearls

    

    The "Maharajah coconut pearl." It was discovered on Celebes Island in the Java Sea and presented to Dr. David Fairchild in 1940. This alleged "pearl" given to Dr. Fairchild was not in its original coconut, so there is substantial doubt as to its authenticity.

    See Disclaimer On The Existence Of Coconut Pearls

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    16. Propositions For The Origin Of Life On Earth

75. Religious debates over the origin of life are often false dichotomous arguments. If the scientific explanation is not adequate then the alternative argument for creation must be true. The problem here is that this debate is not limited to two alternative arguments. There are several scientific hypotheses for the origin of life and numerous explanations for supernatural creation throughout the world. In false dichotomous arguments, if one side is wrong this does not mean that the other side is correct. In true dichotomous arguments there are only two choices. If one side is false then the other side must be true. For example, in a dichotomous key to the duckweed family, one statement says that roots are present, while a second statement says that roots are absent. Only one of these statements is true regarding the duckweed species you are trying to identify.

    See A Simplified Dichotomous Key To The Duckweed Family  See A Flow Chart Dichotomous Key To The Duckweed Family

76. There are literally thousands of non-scientific theories proposed for the origin of life, including intelligent design. Supernatural arguments for the origin of life are not scientific theories because they have no empirical evidence and cannot be tested or proven. They are based on faith in a creator (God). Advocates of intelligent design are very careful not to mention God as the designer. If the "designer" is not God, then is it an intelligent being from another galaxy? Advocates of intelligent design also argue that their "theory" has been tested and the results published in reputable, peer-reviewed scientific journals, but this is simply not the case. In 2004, an Intelligent Design article was accepted by the editor of Proceedings of the Biological Society of Washington without the approval of the Society's governing council. The 250 indignant members of this Society vehemently protested its publication. See "Creationism's Holy Grail: The Intelligent Design of a Peer-Reviewed Paper" by Robert Weitzel in (Skeptic Volume 11 (Number 4) 2005, pages 66-69. Although Charles Darwin mentioned a Creator in some editions of his Origin of Species, there is considerable speculation regarding his religious convictions. In a letter to Mr. J. Fordyce (1879) Darwin wrote: "... In my most extreme fluctuations I have never been an Atheist in the sense of denying the existence of God. I think that generally (and more and more as I grow older), but not always, that an Agnostic would be the most correct description of my state of mind." For more information about Darwin's religious beliefs, please refer to Finding Darwin's God by Kenneth R. Miller, HarperCollins, 1999.

77. The development of life from self-replicating organic molecules in the original "primordial soup" is a scientific hypothesis called biopoiesis. Scientists have created the molecular building blocks of life from gasses in a primitive earth atmosphere. They have also created what appear to be the precursors of cells; however, the precise mechanism and biochemical pathway for biopoiesis remain hypothetical. If one hypothesis does not adequately explain the origin of life, this does not mean that an alternative hypothesis is necessarily true. In fact, there are several hypotheses for the origin of life on earth, including an extraterrestrial origin. One of these is called the panspermia hypothesis which states that the earth was "seeded" by extraterrestrial prokaryotic cells similar to archaebacteria that were carried to earth by meteors. Under a strict definition, a hypothesis must be testable and verifiable before it becomes a scientific theory. Will a scientific theory be developed to explain the origin of life? Only time will tell.

    See Archaebacteria: A Life Form On Mars?

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    17. The Danger Of Imposing Non-Science Dogma In Science Courses

78. Advocates of intelligent design would like to see their dogma taught alongside evolution in science courses. As I have stated in this report, intelligent design is not a scientific theory. It is not based on empirical evidence and cannot be tested or proven. It is dangerous to impose non-scientific dogma in science courses. One case in point is the teaching of acquired characteristics in the Soviet Union between 1948 and 1964. This hypothesis was proposed by the French biologist Jean-Baptiste de Lamarck in the early 1800s, and was actually proposed thousands of years earlier by Greek scholars. According to acquired characteristics, the environment can bring about inherited change. One classic example given by Lamarck is that the long neck of the giraffe developed over time because animals stretched their necks to browse high in trees and then passed on the propensity for a longer neck to their offspring. Although the environment is a factor in evolution, the mechanism of acquired characteristics has been thoroughly disproved during the last century: Phenotypic changes acquired during an organism's lifetime do not result in genetic changes that can be passed to subsequent generations. Potential gene-bearing gametes are set aside in the form of mother cells (oocytes and spermatocytes) early in an animal's embryonic development. The long neck of the giraffe is explained by genetic variabilty and selection for longer-necked offspring over thousands of generations. By the mid 1800s both Charles Darwin and Alfred Russel Wallace independently came up with their hypotheses of "survival of the fittest" to explain the origin of species by natural selection; but it was the Austrian Monk Gregor Mendel who in 1865 first described a mechanism to explain variability and the transmission of traits from parents to offspring. The story behind the teaching of acquired characteristics in the Soviet Union is a good example of why politics and religion should not interfere with scientific research.

79. In 1948, a decree of the Presidium of the Soviet Academy of Sciences appeared in Pravda. It stated that communists must teach and say that acquired characteristics are inherited. All research in agriculture and biology was controlled by Trofim Lysenko, the "dictator of genetic research." Refusal to follow acquired characteristics resulted in the dismissal, exile and execution of a number of Russian geneticists. During the late 1940s and 1950s, the Soviet Union fell behind the rest of the world in genetics research and there was a gradual failure in Soviet agriculture. Shortly after the downfall of Nikita Kruschev in 1964, Lysenko was dismissed from his administrative position. Soviet research in acquired characteristics was exposed as a fraud and the translation of western textbooks containing Mendelian genetics was ordered. The imposition of non-scientific dogma in the Soviet Union for a period of almost two decades resulted in a missing generation of trained geneticists. Politics and religion should not interfere with scientific research or the teaching of science in our schools.

80. As I have stated above in this essay, the K-12 general biology supplement Of Pandas and People contains some misleading information. It also makes some very simplistic comparisons that are inappropriate for an academic science course designed to prepare young minds for the future of science and technology. For example, if we see the words "John Loves Mary" written in the sand, we know that this message was written by an intelligent designer called Homo sapiens sapiens. Then why can't a message written in the DNA of our genes also be made by an intelligent designer? This is another example of an oversimplified comparison. We know from experience that people write messages in the sand. Probably everyone has done this at one time in their life. But we can only hypothesize about the origin of coded messages in DNA, or for that matter, the origin of DNA. We can say that DNA is so marvelous and complex that is must have come from an intelligent designer, but now we are basing our conclusion on faith, not science. That is why intelligent design does not belong in a science class. Although proponents of intelligent design are very careful not to specify who their "designer" is, the logical conclusion is that it must be God. We have freedom of religion in the United States guaranteed by the First Amendment of the Constitution. It is not wrong to believe that our God is the intelligent designer; however, explanations of the natural world based on faith just don't belong in a science class.

81. During the famous Dover School Board Trial of fall 2005, proponents of intelligent design argued that their "theory" was not based on biblical creationism. They even claimed that their recommended supplemental biology textbook Of Pandas and People (2nd. Edition, 2004) did not center around creationism. The latter testimony was repudiated by Dr. Barbara Forest after she discovered early drafts of the textbook with the words "creation" instead of intelligent design. In one draft (pp. 3-41), the word "creationists" was incompletely replaced by the words "intelligent design." It is clear that intelligent design is synonymous with creationism.

    Biology and Creation (1986): Evolutionists think the former is correct, creationists accept the latter view." Biology and Origins (1987): Evolutionists think the former is correct, creationists accept the latter view." Of Pandas and People (1987): Evolutionists think the former is correct, creationists accept the latter view." Of Pandas and People (1987): Evolutionists think the former is correct, cdesign proponentsists accept the latter view."

82. The Biophysical Society is an international society of scientists established to encourage development and dissemination of knowledge in biophysics. The following comes from their concluding paragraph regarding the teaching of alternatives to evolution in K-12 science classrooms (November 5, 2005): "Attempts to suppress or compromise the teaching of evolutionary science in the United States are misguided actions that will deprive our youth of a clear understanding of the scientific process, and of the scientific skills that they need to compete in a global economy: one that is increasingly driven by science and technology. Moreover, current efforts to disguise theology as science do a severe disservice to the scientific profession and to the people of the United States."

83. Since intelligent design is not science, it does not belong in the science curricula of the nation's primary and secondary schools. This is the position statement of the following prestigious scientific organizations: National Academy of Sciences, American Association for the Advancement of Science, National Science Teachers' Association, American Geophysical Union, American Chemical Society, American Association of Physics Teachers, and the American Astronomical Society. All of these organizations emphasize the importance of scientific methodology as well as articulating well-established scientific theories.

    See DNA Structure & Function  See Polymerase Chain Reaction

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    18. Evolution Of Macromolecules & Cells by Random Probability

84. Some authors have used the extrapolation of Darwin's Origin of a Species by Means of Natural Selection to include the first macromolecules and living cells, although this has never been proven through rigorous scientific analysis. They have even speculated that macromolecules and living cells evolved purely by random chance. A functional protein may contain more than 500 amino acids arranged in a specific orderly sequence with a unique 3-dimensional structure. The probability for the 2-dimensional arrangement of 500 amino acids is astronomical. It is equivalent to 1 in 20⁵⁰⁰ or roughly 1 in 10⁶⁵⁰. Some models of the visible universe list 10⁸⁰ for the total number of subatomic particles (or electrons), depending on the reference. William A. Dembski, a staunch proponent of intelligent design has come up with his universal probability bound, a numerical value that gauges the likelihood that a given event could have occurred by chance in nature, or whether it occurred by intelligent design (i.e. by a natural or supernatural intelligence). Dembski's probability bound is a cutoff point between probability and a "creator." It is based on a very improbable number (1 in 10¹⁵⁰), derived from the inverse of the product of several astronomical numbers, including the number of subatomic particles in the universe. Whether this number is the cutoff point between random probability and a creator is impossible to prove. For an intelligent review of Dembski's mathematical explanation for intelligent design, please read "The Dream World of William Dembski's Creationism" by Mark Perakh in Skeptic Volume 11 (Number 4) 2005, pages 54-65.

    See Dembski's Universal Probability Bound

85. Given the plausible conditions and energy forces of a primitive earth atmosphere, the origin of life was probably a lot more likely than simple random probability. Some of these "natural" conditions and forces may have included simple compounds in a "primordial soup," including water, methane, ammonia and hydrogen, shallow pools lined with clay particles bearing electrostatic charges, heat and electrical discharges (lightning), and a time window of countless million of years. Whether a supernatural force was also involved in this process is perhaps one of the most controversial topics ever discussed by educated people.

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    19. Did All Life On Earth Evolve From A Common Ancestor?

86. All life on earth is determined by the same genetic code consisting of the four bases Adenine, Guanine, Cytosine and Thymine. The fact that we also share some of the same DNA sequences (genes) as eukaryotic cells is strong evidence that we are all related. The probability that identical genes evolved independently in diverse organisms is mathematically too unlikely. The following explanation is summarized from Eric Roston's fascinating book entitled The Carbon Age. The thermophilic bacterium Aquifex aeolicus lives in hot springs at Yellowstone National Park in water that is nearly boiling at 95 degrees Celsius (203 degress F). This rod-shaped bacterium 5 micrometers in length has a genome containing 1,551,335 base pairs. Since each base pair has four possible arrangements (see paragraph #15 above), the total number of different DNA combinations for this minute organism is 4^1,551,335. Thats four multiplied by itself 1,551,335 times. Compare this number with 10⁸⁰ or 4¹³³, the total number of electrons in some models of the visible universe. The DNA in a human nucleus contains at least three billion base pairs or 4 ^{3,000,000,000} different sequences. "These numbers are so preposterously large that the likelihood for random overlap is all but mathematically zero. So if human beings and A. aeolicus have any genes--just one--in common, they are not random, and humans and A. aeolicus share a genetic code descended from a single ancestor." In fact, we actually share several dozen genes with A. aeolicus.
    

    A boiling hot spring in Yellowstone National Park containing Aquifex aeolicus, photosynthetic cyanobacteria, and Thermus aquaticus, a heterotrophic bacterium that survives on minute amounts of organic matter in the water. The latter species is the original source of TAQ polymerase used in the amplification of DNA using the polymerase chain reaction (PCR). Scientists from throughout the world are studying the amazing bacteria flora at Yellowstone National Park. This is one of the best places on earth to study these organisms in their natural protected habitats. In other parts of the world, similar hot springs have been destroyed for the production of geothermal energy. Life as we know it may have first arisen more than three billion years ago in a high temperature environment of boiling water. Thermophilic bacteria in hot springs of Yellowstone National Park may be relict populations of the first life on earth. In fact, these thermophilic bacteria may be the ancestors of all other life forms, including humans.

    Wayne's Word Article About Polymerase Chain Reaction  See The Wayne's Word Table Of Cell Size Comparisons

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    20. Addendum: Origin Of The Magnificent Grand Canyon
    

87. Standing on the rim of this enormous canyon and gazing out at the colorful strata representing over a billion years of geologic time, you realize the brief life span of a mortal human. Was this magnificent canyon created in its present form by God, or was it formed during millions of years of sedimentation, uplifting and erosion? If it was underwater during the worldwide biblical flood, how did all the animals become stratified into layers dating back to the Cambrian period over 500 million years ago? Were all these creatures treading water at the same time during the great flood, only to die and settle out in layers?

88. Fossil evidence indicates that numerous species of animals lived during different periods of time. As layers of sediments were deposited, animals from each time period were recorded in the strata as fossils. About 40-70 million years ago, the Grand Canyon region was uplifted into a high plateau during a tremendous mountain building era known as the Laramide Orogeny. This massive uplifting gave rise to the Rocky Mountains and the origin of the Colorado River drainage. During the past six million years, the Colorado River has cut through this high plateau region, as it winds its way to the low Colorado Desert and eventually to the Gulf of California. The river's steep gradient of 8 feet per mile (1.5 m per km) and high sediment load contributed to its cutting power. Rockfalls, landslides, flash floods from torrential rains, and ongoing erosion in tributary canyons, have worked in tandem with the Colorado River to widen the canyon and form the intricate cliff and slope pattern seen today.
    

    Trilobites such as these Elrathia kingi from Utah lived in shallow Cambrian seas. Trilobite fossils are also present in the lower sedimentary strata of the Grand Canyon. They are often placed in the class Trilobita within the phylum Arthropoda. They flourished during the Cambrian period over 500 million years ago. The last of the trilobites disappeared in the mass extinction at the end of the Permian, about 250 million years ago. They are a famous and well-known fossil group, possibly second only to the dinosaurs.

    Fossils Of Ancient Plants & Animals

89. There is overwhelming evidence from paleontology and geology that the Grand Canyon's strata and all of its ancient life evolved during the past 550 million years. To suggest that it was created in its present form, or that all of this occurred during the last 6,000 years as stated in the Bible, is based purely on faith. Some people with a much broader interpretation of the Bible believe their faith does not conflict with the objective scientific evidence.

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    21. True or False Summary Statements

    A scientific theory is an explanation for the cause or causes of complex natural phenomena based on observable facts and rigorous tests that have been repeatedly verified by scientists. Scientific theories are generally more complex and dynamic than scientific laws, and they may be changed as the body of experimental data and analysis develops. Scientific laws are strictly empirical and explain a single action or set of actions; they can sometimes be expressed in terms of a single mathematical equation. Hypotheses are tentative explanations or propositions about the causes of natural phenomena; they are not elevated to the status of scientific theories and scientific laws without rigorous testing and review by scientists. Scientific theories and scientific laws both start out as hypotheses that have been repeatedly tested by scientists and have survived. A scientific theory is a set of statements, including scientific laws, that has been tested repeatedly on new data; it is not subordinate to, or lesser than, a scientific law. A scientific theory is not "just a theory," it is as good as it gets when it comes to explaining complex natural phenomena. Dynamic scientific theories do not necessarily become scientific laws; along with scientific laws they are the foundations of scientific knowledge and together explain our complex natural world. True scientific theories have been developed through the rigorous scientific method; they are much different from "common theories" that are used by laypersons and creationists. Most common theories are only educated guesses; at best they are only tentative hypotheses The "endosymbiont theory" should be called the "endosymbiont hypothesis." Symbiogenesis is technically a scientific hypothesis rather than a scientific theory. Some scientists incorrectly use the term "theory" to explain phenomena that has not been repeatedly tested and verified by the scientific method. One scientist cannot create a scientific theory. A scientific theory should not be called a fact. It is still Einstein's "theory of relativity," even though it is probably as close to a fact as anyone can get in science. Even though it has survived the test of time and has passed all tests so far, it is still subject to challenge as the body of experimental data and analysis develops. A common or layperson's theory is equivalent to an educated guess or hunch. All facts in science are provisional and subject to challenge. The scientific theory of evolution assumes the existence of life and is directed to an explanation of how life evolved. The scientific theory of evolution does not deal with the origin of life, and it does not presuppose the absence of a creator or God. Scientific explanations for the origin of life are more properly referred to as hypotheses rather than scientific theories. Intelligent design is a non-scientific (non-testable) argument or assertion that life owes its origin to a master intellect. According to creationists, all life originated abruptly in its present form. Faith is the belief in the existence of something without proof or verifiable empirical evidence. Politics and religion should not interfere with scientific research or the teaching of science in our schools. The existence of true coconut pearls is based on faith rather than empirical evidence. Intelligent design as the only alternative to evolution is a false dichotomous argument. The argument whether evolution is a theory or a fact is an invalid comparison. The evidence showing that life evolved on this planet is overwhelming; however, the exact mechanism for the origin of life is hypothetical. Biopoiesis is a scientific hypothesis for the origin of life from self-replicating organic molecules in the original "primordial soup." Panspermia is a hypothesis which states that the earth was "seeded" by extraterrestrial prokaryotic cells similar to archaebacteria that were carried to earth by meteors. Natural selection is a well-tested and verifiable mechanism to explain the origin of species according to the scientific theory of evolution. Genetic variability is the raw material for evolution. The evolution of many species in a new habitat from an ancestral species is called adaptive radiation. The remarkable "Silver Sword Alliance" and the unusual lobelioids on the Hawaiian Islands is a good example of adaptive radiation. The word "theory" is commonly used by scientists and lay people for tentative explanations that have not been universally tested and accepted by the scientific community. In this case, the term hypothesis is more appropriate. The word "theory" is commonly used by scientists and lay people for explanations that have been repeatedly verified and universally accepted by the scientific community. In this case, the term scientific theory is more appropriate. The African euphorbias and North American cacti are classic examples of convergent evolution. Parallel evolution is similar to convergent evolution, except the organisms being compared may not have an overall resemble to each other. The noun "theory" associated with time-tested explanations such as evolution, relativity and plate tectonics, should be modified by the adjective "scientific" in order to distinguish it from a "common" or "layman" theory that is essentially a tentative explanation or untested hypothesis. Using the term homoplasy avoids the confusing distinction between parallel and convergent evolution. The origin of the eye is different phyla of animals is probably not a good example of homoplasy. Humans once had 24 pairs of chromosomes like present-day great apes (orangutans, gorillas and chimpanzees). Contrary to anti-evolution propaganda, there are many excellent examples of "missing links" in the fossil record, evolutionary transitions between distantly related animal groups. Fossils known as "missing links" represent major phylogenetic branches (clades) giving rise to successive levels of life on earth. Evolution is best explained as a well-established scientific theory based on numerous facts. Click Here For Answers To The Above Questions

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