Why Darwin's evolutionary theory doesn't imperil the foundations of knowledge.

Aristotle Can't Refute Evolution: 

A Response to Seagrave

by Robert T. Miller 

While evolutionary theory shows us that we can't divide living things into stable, distinct species, this doesn't mean that it imperils the foundations of knowledge.

Here at Public Discourse, Adam Seagrave (see his original post here) has been discussing evolution with Stephen Barr and Kenneth Kemp. In his latest essay, Seagrave argues that, since Darwinian evolution makes the various species of living things not real and immutable features of objective reality but merely useful ways for human beings to organize and categorize that reality, Darwin imperils the foundations of human knowledge.

In particular, Seagrave relies on the Aristotelian doctrine that human knowledge is ultimately founded on a process of induction or abstraction from sense experience, "a process that allows equal access on the part of the layman and specialist alike." From this common experience, we come to know "stable and defined universal concepts," including the various species of living things, which "form the building blocks of all subsequent knowledge." Hence, "the very way in which we human beings know the world around us ... is inextricably bound up with the stability and distinctness of the types of things, or 'species,' we observe." Because evolutionary theory "carries with it a decisive rejection of the truth of this stability and distinctness of species or types of things," it undermines the foundations of human knowledge and entails "a repudiation of our fundamental intellectual affinity with the world around us."

I think quite a lot has gone wrong here. Regardless of how we come to have universal concepts, and assuming for the sake of argument that things have essences in the way Aristotle thought, it is clear that the concepts of our common experience do not generally correspond with the essences or species of things. For example, it is certainly essential to elephants that they have DNA, are composed of cells, and circulate their blood, but we learn these things from laborious scientific investigation, not from studying the concept elephant or from casually observing elephants. Similarly, it is essential to gold that the atoms of which it is composed have 79 protons in their nuclei, but people had a concept of gold for millennia before we learned this fact from atomic theory.

Moreover, sometimes our common experience positively misleads us about essences. A man who regularly sees caterpillars and regularly sees butterflies but never witnesses the process of metamorphosis would think that these were animals of two different species, not one. And, to take a famous example from the history of science, for centuries everyone thought that "jade" named a single kind of mineral until, in 1863, Alexis Demour discovered that passing under the single name "jade" were two chemically distinct substances--nephrite and jadeite--that are indistinguishable by casual observation. Again, our concepts do not match up with the essences of things.

Nor does this divergence between our concepts and essences depend on modern scientific examples. On the contrary, it was well-understood in the Aristotelian tradition. Thus, Thomas Aquinas, as a good Aristotelian, often said that we do not generally know the essences of things, once remarking that a philosopher could spend a lifetime studying a fly and not achieve a full knowledge of its nature.

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