Chapter 2
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Chapter 2 EVIDENCE FOR EVOLUTION
I. Introduction. As I understand it, Darwin's theory of evolution by natural selection is that all living organisms descended from a small number of common ancestors, and perhaps a single microscopic, single-celled organism, as a result of a process called "natural selection." According to this theory, any attributes which conferred an advantage upon an individual organism in the competition for survival were more likely to be passed on to succeeding generations, because such an organism was more likely to survive long enough to procreate. Such attributes would be disproportionately preserved. Over great periods of time, such advantageous attributes would accumulate until the organism was so different from its ancestors as to constitute a new species entirely. In this way, over billions of years, all the biological diversity now extant on the earth was gradually developed. So the theory goes. Arguably, there are two things which together constitute the most compelling body of evidence in favor of the theory of evolution: the many similarities among living organisms, and the progressivity of the fossil record. There are three major types of similarities among organisms: morphological, genetic, and biochemical. Morphology, or physiognomy, has to do with the body shapes of living things. The plant and animal kindgoms are filled with vast numbers of organisms which can be categorized in groups according to similarities in their body parts. Cats are all similar; yet lions, tigers and housecats are all separate species. According to the theory of evolution, they all have a common ancestor, and it is this common ancestry which explains - which, indeed, caused their physical similarities. Anyone could multiply such examples almost indefinitely. At the same time, the fossil record to some extent shows that similar organisms appeared near in time and place to each other, creating a clear impression of development. These aspects of the fossil record would be consistent with an evolutionary model in which the simplest single-cell organism originated from non-living material, and developed with time into more and more complex forms. As Kenneth Miller observes: What impresses one most about the fossil record is its sequential character. Why, you might ask, do the geological ages contain so many apparent evolutionary sequences if evolution never took place?1 According to Phillip Johnson, Douglas Futuyma has done the best job of marshalling the affirmative evidence for the effectiveness of natural selection. Johnson summarizes Futuyma's survey as follows. (1) Bacteria naturally develop resistance to antibiotics, and insect pests become resistant to insecticides, because of the differential survival of mutant forms possessing the advantage of resistance. (2) In 1898 a severe storm in Massachusetts left hundreds of dead and dying birds in its wake. Someone brought 136 exhausted sparrows to a scientist named Bumpus, I imagine so they could be cared for, but Bumpus was made of sterner stuff and killed the survivors to measure their skeletons. He found that among male sparrows the larger birds had survived more frequently than the smaller ones, even though the size differential was relatively slight. (3) A drought in the Galapagos Islands in 1977 caused a shortage of the small seeds on which finches feed. As a consequence these birds had to eat larger seeds, which they usually ignore. After one generation there had been so much mortality among the smaller finches, who could not easily eat the larger seeds, that the average size of the birds (and especially their beaks) went up appreciably. Futuyma comments: "Very possibly the birds will evolve back to their previous state if the environment goes back to normal, but we can see in this example what would happen if the birds were forced to live in a consistently dry environment: they would evolve a permanent adaptation to whatever kinds of seeds are consistently available. This is natural selection in action, and it is not a matter of chance." (4) The allele (genetic state) responsible for sickle-cell anemia in African populations is also associated with a trait that confers resistance to malaria. Individuals who are totally free of the sickle-cell allele suffer high mortality from malaria, and individuals who inherit the sickle-cell allele from both parents tend to die early from anemia. Chances for survival are greatest when the individual inherits the sickle-cell allele from one parent but not the other, and so the trait is not bred out of the population. Futuyma comments that the example shows not only that natural selection is effective, but also that it is "an uncaring mechanical process." (5) Mice populations have been observed to cease reproducing and become extinct when they are temporarily "flooded" by the spread of a gene which causes sterility in the males. (6) Finally, Futuyma summarizes Kettlewell's famous observations of "industrial melanism" in the peppered moth. When trees were darkened by industrial smoke, dark-colored (melanic) moths became abundant because predators had difficulty seeing them against the trees. When the trees became lighter due to reduced air pollution, the lighter-colored moths had the advantage. Kettlewell's observations showed in detail how the prevailing color of moths changed along with the prevailing color of the trees. Subsequent commentators have observed that the example shows stability as well as cyclical change within a boundary, because the ability of the species to survive in a changing environment is enhanced if it maintains at all times a supply of both light and dark moths. If the light variety had disappeared altogether during the years of dark trees, the species would have been threatened with extinction when the trees lightened.2 [T]he structures preserved within the fossil make it clear that Acanthostega could breathe with its gills underwater, just like a fish, and could also breathe on land, using lungs. It was a true transitional form. This first amphibian-like tetrapod was, as evolution would have predicted, more fish-like than any tetrapod to follow. . . .3 And we must not, of course, neglect to mention Archaeopteryx, a creature with feathered wings and a wishbone but also reptilian features like claws on its wings and teeth in its mouth. Discovered shortly after the publication of Origin of Species, Archeopteryx had a lot to do with the initial success of Darwin's theory. Additionally, the existence of "vestigial" organs has been cited as evidence for evolution. Futuyma mentions the "rudimentary eyes of cave animals; the tiny, useless legs of many snakelike lizards; [and] the vestiges of the pelvis in pythons" as evidence that evolution has occurred. Such structures must be explained, he contends, by an ancestry for the animal containing a much different progenitor. Miller also cites the existence of "pseudogenes" which lack the information necessary to cause the production of proteins, and claims that these are explained by an evolutionary process of trial and error which could not "see" where it was going and so sometimes led nowhere in particular.5 As suggestive as the evidence for natural selection may be, none of it shows that Darwinian evolution must or even could have occurred. The most that could have been said (prior to the recent findings of molecular biochemistry and cosmology) was that Darwinian evolution was not impossible, as far as we knew. If it should appear, then, that there is evidence which makes evolution by natural selection seem to be categorically impossible, we would be justified in saying that none of the evidence for Darwinism, as suggestive as it might otherwise be, would be entitled to much weight. Before proceeding to consider such counter-evidence (Chapters 4 through 7), however, let us first see what reasons have been offered for skepticism toward the affirmative evidence for evolution summarized above. Endnotes 1Kenneth R. Miller, Finding Darwin's God, (New York: Harper Collins, 1999), p. 61. (Emphasis in original.) 5There is one other prominent line of evidence, but I was unaware of its importance when I completed this essay. In Darwin's God (Grand Rapids: Brazos Press, 2001), Cornelius Hunter shows that beginning with Darwin through to the present time, evolutionists have appealed to their view of the character of God and insist that God could not have been responsible for a natural order in which inefficiency, waste, and violent death are so prevalent. Since those conditions do prevail, they argue, that order must have arisen through some impersonal cause. Time permitting, I shall soon add an appendix recapitulating Hunter's thesis more fully. © 2002 Thomas O. Alderman |
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