A post now up at the Philosopher’s Carnival discusses Alvin Plantinga’s Evolutionary Argument Against Naturalism (EAAN), and comment how it is like (not exactly the same) as a global skepticism argument being self-defeating. Plantinga’s argument goes like this:
P1. If evolution is true, then we have modified monkey brains.
P2. Modified monkey brains are not evolved to find out the truth
P3. Evolutionary naturalism (the view that everything about humans, including their cognitive capacities, evolved) is the output of modified monkey brains.
C1. Therefore evolutionary theory is unreliable and should be rejected.
C2. Therefore evolutionary naturalism should be rejected.
The modified monkey brain comes directly from Darwin’s letter to William Graham, in which he wrote
Would any one trust in the convictions of a monkey’s mind, if there are any convictions in such a mind?
Plantinga directly mentions this letter, and argues that in effect if evolution is true it cannot be rational to believe that it is. The trouble with this argument is that this is exactly there opposite conclusion to the one that Darwin made. Darwin’s full argument, made in response to Graham’s book The Creed of Science, is this:
You would not probably expect anyone fully to agree with you on so many abstruse subjects; and there are some points in your book which I cannot digest. The chief one is that the existence of so-called natural laws implies purpose. I cannot see this. Not to mention that many expect that the several great laws will some day be found to follow inevitably from some one single law, yet taking the laws as we now know them, and look at the moon, what the law of gravitation — and no doubt of the conservation of energy — of the atomic theory, &c. &c. hold good, and I cannot see that there is then necessarily any purpose. Would there be purpose if the lowest organisms alone destitute of consciousness existed in the moon? But I have had no practice in abstract reasoning and I may be all astray. Nevertheless you have expressed my inward conviction, though far more vividly and clearly than I could have done, that the Universe is not the result of chance. But then with me 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?
So what Darwin is arguing is that evolution gives us no confidence in metaphysical conclusions, not science. Science he takes for granted can be undertaken by modified monkey brains. They evolved to find out about the world. What evolution undercuts is the ability of monkey brains to form reasonable convictions about things like Gods and Cosmic Purpose.
Plantinga knows this, and even mentions it in a footnote but he disingenuously inverts the argument and makes it look as if Darwin was riven with doubts about his own theory. Of course he was not. This is rhetorical prevarication by omission. But the argument Darwin makes is much more interesting than a simple global skepticism. He is arguing that we can know about the world, due to our evolved faculties.
Why is that? Why can our evolved faculties make beliefs about the world reliable, but not beliefs about gods and angels? The answer is simple, according to an argument Paul Griffiths and I have made in two forthcoming book chapters: some beliefs are truth tracking because they contribute to fitness when they are true and lower fitness when they are not, while beliefs about gods and purpose in the cosmos do not in virtue of their content, but only in virtue of their being consonant with the society of the believer.
Another way to put this is that there are environmental beliefs that must be true (or at least not egregiously false) in order to improve the fitness of the belief-holder, and there are social beliefs that affect fitness in virtue of what other people also believe and how they react to the belief holder. Morality, aesthetics and most of all religion are of the latter kind. Assuming that the religious beliefs do not insist upon too many fitness lowering behaviours (like snake handling) in ways that are not balanced or exceeded by the fitness benefits of being a believer, a religious belief increases fitness only to the extent that others share it, whereas an environmental belief (like whether that food is poisonous when treated with alkaline soils, or whether the stars are reliable guides to hunting or planting seasons) increases fitness when it is true (or not too false). In other words, an environmental belief had better give not too many false positives and not too many false negatives about the way the world is, while a social belief had better give not too many false positives and negatives not about the content of the belief, but about what others around you believe also. In short, people are the environment for social beliefs, not gods, or cosmic anythings.
So if properly understood, Darwin’s argument undercuts Plantinga’s anti naturalism and in fact replaces it with a global skepticism about the non-natural, and this is not self-defeating. Plantinga’s EAAN is actually an EAAS[upernaturalism].
Refs below the fold