Evolution, the Eye Test, & Scientific Reasoning: A Response to Seagrave


The “eye test” is no more a problem for the evolutionary origin of species than it is for the atomic structure of matter or for the motion of the earth.

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In his recent contribution to Public Discourse, Adam Seagrave argues that Darwin’s evolutionary theory presupposes that “our senses don’t tell us the truth about nature.” In this, and in his general characterization of the battle between evolutionists and anti-evolutionists, I believe he is mistaken.

Seagrave begins by remarking that “the longstanding evolution debate has traditionally pitted proponents of science against proponents of religious belief.” Although there are atheists (e.g., Richard Dawkins) who claim evolutionary-biological warrant for their attacks on religion and Christians (Creation-Scientists and Intelligent-Design Theorists) who claim theological confirmation of their anti-evolutionism, Seagrave’s remark is misleading.

He hints at the existence of a war between science and religion when the most he is entitled to say is that some scientists have mistaken their philosophical views for science and that some Christians reject evolutionary biology for theological reasons. Many Christians (e.g., Pope John Paul II and Notre Dame professor of philosophy Fr. Ernan McMullin) have found no problem accepting evolutionary biology, and many evolutionary biologists (e.g., Brown University biologist Kenneth Miller) also accept Christian theology.

It would be more insightful (and more closely connected to his argument) to highlight another feature of the battle over evolution. Although Darwin’s theory explains a wide array of facts from paleontology, biogeography, comparative anatomy, systematics, and embryology, these are facts that are generally unknown to laymen.

Non-biologists simply do not wonder why the fauna of the Cape Verde Islands resemble precisely the fauna of the nearest mainland, or why the structure of bat wings resembles that of whale flippers. They do wonder how a species that lacks wings could ever turn into a species that has them. This lack of wonder about the features of the world that Darwin is trying to explain, combined with the somewhat counterintuitive nature of Darwin’s solution (which, to highlight the paradox, attributes a common ancestry to beetles and whales) generates much of the skepticism that Darwinism continues to face. As Darwin wrote:

Any one whose disposition leads him to attach more weight to unexplained difficulties than to the explanation of a certain number of facts will certainly reject my theory.

Seagrave contrasts science, religious belief, and philosophy with the acceptance of what our eyes and senses tell us, and argues that if evolutionary biology is true, then our senses are deceptive. Surely his eye test is far too strong. Our senses, when used cautiously, are not deceptive, but they do not by themselves get us beyond facts about our immediate environment. To get beyond those to explanations of those facts (i.e., to theories), we need another tool—reason.

Seagrave objects to three particular Darwinian ideas—one related to Darwin’s natural selection thesis and two related to his common ancestry thesis. Accepting these ideas, he claims, would force us to accept that “the world is nothing like our experience of it.” But none of these ideas carries that implication.

The first Darwinian idea is that there is a struggle for existence. But how far is this struggle from what we see with our own eyes? What does Seagrave think songbirds eat? Haven’t we all seen robins eat worms? For that matter, what do he and I eat? We know from experience what happens to deer when the wolves die off. Darwin wrote, “A struggle for existence inevitably follows from the high rate at which all organic beings tend to increase,” and illustrated it with an example:

The elephant is reckoned to be the slowest breeder of all known animals, and I have taken some pains to estimate its probable minimum rate of natural increase: it will be under the mark to assume that it breeds when thirty years old, and goes on breeding till ninety years old, bringing forth three pair of young in this interval; if this be so, at the end of the fifth century there would be alive fifteen million elephants, descended from the first pair.

Where does Darwin go wrong in that inference? What is Seagrave’s answer to the question of why the world is not full of elephants? How exactly do our senses show us a world in which there is no struggle for existence?

The second Darwinian idea is that natural selection can form “organs of extreme perfection and complication,” such as the eye. Darwin does briefly suggest how natural selection might have produced organs as complex as the eye, a suggestion that has been successfully elaborated by subsequent generations of biologists. Does accepting that account require that one judge the senses to be deceptive? Evolutionary biologists claim that morphological changes of this magnitude occur over the course of a few million years. Observation shows that changes of this magnitude seem not to occur over the course of a few thousand years. Where is the contradiction? In what way are our senses deceiving us?

The third (allegedly) Darwinian idea is that species are not fixed and distinct. Seagrave says that “as far as we know from direct observation and recorded history . . . squirrels [seem] to have always been squirrels.” But “squirrel” is not a species name; there are about 50 genera of squirrels and some 273 species. So, it’s hard to know exactly what Seagrave means when he says “squirrels [seem] to have always been squirrels.”

Is he claiming that one species never gave rise to another species? Duke University biologists John M. Mercer and V. Louise Roth have shown how DNA evidence from today’s squirrel species can be combined with geological and paleontological evidence to give a coherent account of the evolutionary divergence of squirrels—one early species of squirrels (something like Douglassciurus jeffersoni, known from the fossil record) having given rise, over the course of 36 million years, to many other species (ranging from flying squirrels to prairie dogs). The claim that squirrel species have not been observed to split into two species over the course of ten thousand years and the claim that an original squirrel species has given rise to 273 different squirrel species over the course of 36 million years do not contradict one another.

Or is he claiming rather that the whole family of squirrels came into being without any pre-squirrel ancestors? If that is his view, where did they come from? They have not always been here. They cannot be found in any geological formations earlier than the late Eocene. It is not so clear that Darwin’s idea—squirrels are the modified descendants of non-squirrel rodents—simply fails the eye test. Descent with modification is, after all, what we see in the work of, for example, pigeon breeders. Maybe nature can do more in 36 million years than breeders can do in a few thousand. Descent with modification also explains squirrels’ morphological and genetic similarity to other rodents and the fact that they appear in the fossil record only after the appearance of the first rodents, just when they should. Does anyone have another idea of where squirrels came from, an idea that will explain as much and do better on the eye test?

Evolutionary biology claims that species are related to one another in particular ways. Other ways (W.S. Macleay’s quinarian system, to cite just one example) have been proposed over the course of the history of biology and found wanting. The idea that evolutionary biology proposes a “fluid and formless continuity” is an invention of Seagrave’s. What Darwin says is rather that

It is a truly wonderful fact—the wonder of which we are apt to overlook from familiarity—that all animals and all plants throughout all time and space should be related to each other in group subordinate to group . . . To the best of my judgment, it is explained through inheritance and the complex action of natural selection.

In conclusion, evolutionary biology is not as discrepant with the testimony of our senses as Seagrave claims. The “eye test” is no more a problem for the evolutionary origin of species than it is for the atomic structure of matter or for the motion of the earth. To reach any of these truths we need to go beyond what we see ourselves. We need to rely on reason, a faculty that we need if we are to be fitted to the world we seek to understand. In the end, Seagrave seems to concede all that. He does not seem to realize how fully his concession undercuts everything that he said against evolutionary biology at the beginning.

Kenneth Kemp is an associate professor of philosophy at the University of St. Thomas in St. Paul, Minnesota.

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