Darwin's Doubt

I recently read a 1994 paper by Dr. Alvin Plantinga entitled Naturalism Defeated. You can read it yourself here.

It presents a fascinating argument that serves as an undercutting defeater against naturalism and evolution.

Let me back up and define what defeaters are. A defeater is an argument that weakens a knowledge claim. Defeaters can either be rebutting defeaters or undercutting defeaters.

Imagine a court setting. An alibi is a rebutting defeater against the prosecution's case (a reason for thinking the accused is innocent), while impugning the reliability of a key witness is an undercutting defeater (it does not give reason to believe the accused to be innocent, but it casts doubt on the reasonableness of believing him – on the basis of his testimony – to be guilty).

Plantinga zeroes in on what he calls "Darwin's Doubt".

Darwin himself expressed this doubt: "With me," he said, "the horrid doubt always arises whether the convictions of man's mind, which has been developed from the mind of the lower animals, are of any value or at all trustworthy. Would any one trust in the convictions of a monkey's mind, if there are any convictions in such a mind?"(written in a letter to William Graham, Down, July 3rd, 1881.)

Think about what Darwin is saying. Our cognitive faculties are ostensibly derivatives (memory, perceptions, reasoning) of a monkey's mind … whose cognitive faculties are in turn derivatives of a lower mammal … and so on. Does this fact give us confidence in the reliability of our cognitive faculties? The obvious answer is no.

Patricia Churchland makes the same observation. She insists that the most important thing about the human brain is that it has evolved; this means, she says, that its principal function is to enable the organism to move appropriately: Boiled down to essentials, a nervous system enables the organism to succeed in the four F's: feeding, fleeing, fighting and reproducing. The principle chore of nervous systems is to get the body parts where they should be in order that the organism may survive.

In other words, evolution is only interested in adaptive behavior, not in true belief. Does natural selection directly care about what you believe? No. Does it care about how you behave? Yes. It selects for certain kinds of behavior, and the genes of those with fitness enhancing behavior are widely represented in the next generation.

The question is, then, how does belief affect behavior?

Everything turns on this question. Assuming evolution were true, our cognitive faculties would be reliable if it could be shown that it is impossible or unlikely that creatures with false beliefs could behave in fitness enhancing ways. But is this impossible or unlikely? What would or could be the relation between belief and behavior?

We'll take a look at that next time.


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