Science in Christian Perspective

Letter to the Editor


Evolutionary Theory Misunderstood

Dr. David Lahti, ASA Student Member
Museum of Zoology and Department of Biology
University of Michigan  

From: PSCF 52 (September 2000):215-217.

I am proud to be a member of ASA, without doubt America's foremost organization to foster study of the relationship between science and Christianity. In the hope of a continued strengthening of this organization, I respectfully offer criticism of two papers. Specifically, both J. Bergman and M. C. Morris published papers critical of evolutionary biology in a recent issue (PSCF 52 [March 2000]: 18-30, 55-7). I believe that the theses of both are based on misunderstandings of biology.

Bergman claims that the vertebrate eye, with its "inverted" retina, is not a poor design relative to a "verted" retina, contrary to the views of prominent figures like R. Dawkins, G. C. Williams and J. R. Diamond. Bergman defends this claim in two portions: (1) "no evidence exists to support the claim that the most advanced verted eye is superior to the inverted eye," and (2) "If the human retina were verted, we have no evidence that vision would be better. Most likely it would be worse." To support the first statement, Bergman shows how even the most advanced extant cephalopod eye is inferior in function to the vertebrate eye. This is irrelevant to the point of the biologists cited in the beginning of the paper, however. Their point is not that a verted eye better than our own exists somewhere on earth, but that the inverted structure we have is not the optimal design from a theoretical standpoint. The verted design can be functionally superior to the inverted per se regardless of whether any verted eyes in existence are functionally better than any inverted eyes. It is far from surprising, then, that biologists have not sought evidence for better vision in the octopus than the human.

The second portion of Bergman's claim is defended by a physiological account of how vertebrate eye functionality would be altered if the retina were manipulated to the verted design. He rightly claims that problems as diverse as sensory overload and ultraviolet damage would probably result from such a manipulation. This too is irrelevant to the point at hand, however, since no one has postulated that eye functionality would improve with such a manipulation. Rather, the point is that if vertebrates had evolved an eye in the verted design, our vision would have developed more efficiently because of, among other things, the forward orientation of the sensory cells and the lack of a break in the retina to accommodate the optic nerve. An understanding of natural selection makes plain that, had evolution proceeded differently, and humans were walking around today with verted eyes, we would not be experiencing sensory overload and painfully shading our eyes from UV damage. No evolutionary biologist would propose the ridiculous notion that a physician could mimic an alternative course of evolution by surgically reverting the retina which has evolved in an inverted situation. Both parts of Bergman's thesis, therefore, are based on misunderstandings of the evolutionary biologist's claim about the eye, and of the way evolution works.

Other evidence of a misunderstanding of evolution can be found in the paper. "Darwinists," Bergman writes, claim that "the natural world is in fact not designed." In fact, Darwinists do claim that the natural world was designed, and is still being designed. Evolutionary biology indicates natural selection as the mechanism by which design was and is being effected, though of course biology has nothing to say about either the "purpose" or "agent" of this design in a metaphysical or theological sense. The idea of optimization is central to evolutionary biology, and optimization is the hallmark of design; and we do see much evidence of such optimization, such design, in the vertebrate eye, despite the inversion of its retina.

Another profound misrepresentation of evolution lies in Bergman's claim that no "transitional forms" or other evidence supports the evolution "from the primitive verted type common to invertebrates into the inverted eye of vertebrates." No biologist claims that extant invertebrates such as the octopus evolved into extant vertebrates such as humans; to suggest this is to commit the most basic error in thinking about evolution. All extant organisms are the tips of long branches, and no morphological structure on one tip is inherited from that of another. In fact, evolutionary biology concludes that modern cephalopods and vertebrates share their most recent common ancestor very early in animal evolutionary history, at the split of the deuterostomes and protostomes hundreds of millions of years ago. The "primitive" situation is clearly not the verted retinal structure, but no retina at all! The pinhole eye of cephalopods and the lens eye of vertebrates have evolved independently from each other, and from the compound eye of insects. To suggest that we look for transitional forms between these types of eyes is illogical. There is absolutely no disagreement in evolutionary biology about these particulars, and any respected introductory biology text presents this same situation.1

Morris's paper on altruism in nature commits similar errors in that his thesis is based on a misrepresentation of basic biological principles. Morris claims that "Darwinian mechanisms" cannot explain instances of altruism in nature, so we should see the instances of such altruism as "proof of God's creation." After describing a few means whereby evolutionary theory predicts complex interaction among individuals that can be loosely termed "altruism" (although without the psychological or intentional connotation of that term), Morris goes on to suggest that instances of cooperation in fish, ants, plants, and even cells are inexplicable by these mechanisms. On the contrary, clear explanations in biology are widely known to apply to all of these circumstances. These four explanations show how the evolution of such complex behavior can follow directly from the basic principles of evolutionary theory. This having been said, these evolutionary explanations are, of course, silent on the issue of whether God created the world or, if so, why he created it the way he did.

1. Cleaner fish--predator interactions: The benefits to cleaner fish and predators are simultaneous, and therefore no net fitness cost is incurred by either individual. The fact that predators do not eat the cleaner fish simply illustrates that the benefits to the predator of having parasites removed from their mouths is greater than the benefits that would be gained--either nutritionally or by decreasing the cleaners' aid to competitors--by eating the fish.

2. Ant--caterpillar interactions: Concerning the interactions between ants and caterpillars, Morris claims that caring for caterpillars or their pupae after their period of usefulness has passed "would not be advantageous from a Darwinian point of view." This is clearly false. Imagine the difference between two populations of ants: one that ate or ignored post-productive caterpillars, and another that continued to care for them. More caterpillars would reach reproductive maturity and lay eggs in the vicinity of the more helpful ants. Thus, the more helpful ants over the generations would be more successful than the less helpful ants because of the more substantial population size of the caterpillars that produce their food. Seeing the populations in an evolutionary (Darwinian) perspective again renders the situation easily explicable.

3. Neighbor interactions in plants: The exploitation by neighbors of protective substances emitted by a plant is explained in very straightforward terms in evolutionary biology. The production of a protective substance will be naturally selected in plants even if neighbors can benefit from it, as long as the benefit accruing to one genetic individual of producing the toxin is greater than the cost. This cost includes the energetic expenditure of producing the toxin, as well as any competitive cost of helping unrelated neighbors. The relevant benefit here is that instead of being destroyed, the plant is only partially eaten, or not eaten at all if the herbivore knows (e.g., by experience) to avoid the plant. So it is easy to see why such toxin production continues from an evolutionary perspective. In fact, in these harsh habitats where such toxins are common, neighboring plants may gain more mutual benefits by facilitation than they would harm by competition. This added layer of complexity is still squarely within the Darwinian framework. (It is similar to the cleaner fish-predator interaction.)

In many cases, even the moderate level of explanation just offered is unnecessary to account for plants benefitting their neighbors. First, many plants are significantly clonal, such that nearby stems may appear to be separate individuals but are actually genetically identical to each other. Even complete sacrifice of a portion of a genetic individual (in botanical terms, one or more ramets) would be predicted by evolutionary theory if benefits accrued to the genetic individual's survival and reproduction as a whole. Second, plants whose seeds germinate close to them (i.e., plants with limited dispersal) will tend to be clustered, such that neighbors are much more likely to be genetically related than would be expected by chance. In these instances, benefitting one's neighbors is benefitting one's genotype as it is instantiated in closely related individuals (kin selection).

4. Endosymbiosis: The last specific instance Morris provides of supposedly evolutionarily inexplicable altruism in nature is the "cooperation" between cells that is hypothesized to have taken place in the early evolution of eucaryotes. This interaction involves the symbiosis of a bacterium and a larger cell, where one individual resides within the other, each reaps simultaneous benefits from the interaction, and there is no net fitness cost of doing so. Such an interaction is one of a class called mutualism, which is an extremely common and evolutionarily straightforward situation. On the other hand, in instances where there is a fitness cost to an organism of harboring another, the symbiotic interaction is labeled parasitism. Morris assumes that evolutionary biology predicts that all symbioses are parasitic, which is simply not true.

Therefore, all of the examples Morris adduces in support of his thesis that Darwinian mechanisms cannot explain altruism in nature are misguided. Moreover, the errors committed are on points so fundamental to biology as to exhibit a serious lack of consideration of the science. In actuality, more complex and difficult situations than the ones Morris presented do exist in nature, where biologists are still attempting to determine what evolutionary mechanism resulted in certain types of complex social behaviors. Even if some of these had been cited instead of the relatively uncomplicated examples above, biologists know better than to bank heavily on our lack of understanding of natural phenomena. A more successful, more humble, and theologically more respectable attitude is to admit our present ignorance, and search for an answer with an open mind.

Incidentally, the above instances have nothing to do with the notion that "all human morality can be reduced to the random action of selfish genes," which Morris falsely claims to be "the inevitable logical conclusion" of Darwinian mechanisms. This issue is another one altogether, but as Morris does not expound upon it, neither will I.

These two papers offer arguments that exhibit misunderstanding of elementary principles of modern biology. The arguments are actually based on these misunderstandings and cannot be sustained without them. As suggested in my above argumentation, the errors committed in these papers could have been corrected with an attention to any of the many thorough introductions to general biology or evolutionary biology which are in wide use today (e.g., those by Campbell, Keeton and Gould, Purves et al., Futuyma). Certainly a reviewer with a professional background in the disciplinary area germane to the papers would be expected to have caught such gross misrepresentations. I take this opportunity to offer criticism so that an awareness of the problems involved may develop in prospective authors, and so that the reviewing process for the journal may continue its growth in scientific attentiveness.


1E.g., William T. Keeton and James L. Gould, Biological Science, 5th ed. (New York: W. W. Norton, 1993), 673, 1038.