By James Bishop| If human beings are a result of the evolutionary process then one needs to maintain that the main purpose of our cognitive faculties is for survival and reproductive fitness. In other words this process couldn’t care less for true belief, argues philosopher Alvin Plantinga. Evolution only cares whether or not our actions are adaptive and whether or not they contribute to our fitness. Therefore, the naturalist would be incorrect to expect that his faculties would be aimed at truth as they would solely be aimed at fitness.
Now, the implications for the naturalist are significant. If one’s mind is aimed at survival then it follows that the mind cannot be trusted when it thinks it knows the truth. This would undermine the trustworthiness of the human cognitive faculty as atheists themselves such as Friedrich Nietzsche and Thomas Nagel have noted. Even Charles Darwin, the mind who established that all species of life descended over time from common ancestors, likewise saw this dilemma:
“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 anyone trust in the convictions of a monkey’s mind, if there are any convictions in such a mind?”
“This argument,” continues Plantinga, “has to do with the reliability of your cognitive faculties like memory and perception, intuition, and mathematical or logical intuition… I think if you accept naturalism and evolution you can’t think of your cognitive faculties as being reliable, as giving you the actual truth about the world… The argument goes like this. If you’re a naturalist you will probably also be a materialist about human beings. You’ll think that human beings are material objects.
They are not immaterial souls that have a body. Now suppose we think about some creatures on an alien planet that are a lot like us. Let’s suppose for them that naturalism holds, that evolution holds, and that these creatures are material objects. So what is it that causes their behaviour? What causes their behaviour will be neurology, the states of which their neurons are firing sending a signal down to a muscle causing it to contract. And their beliefs and the content of these beliefs are also caused by neurology. Now given that evolution is true these creatures have come into being by virtue of natural selection we can take it for granted that their behaviour is adaptive, it enhances their fitness which leads to survival and reproduction.
If that is true the same thing will go for what causes their behaviour, namely their neurology which also promotes survival and reproduction. The neurology that causes their behaviour also causes their beliefs, but now the question is “suppose their behaviour is in fact adaptive what about the truths of these beliefs?” Well, I think that you can see that it doesn’t matter about the truths of these beliefs.
If their neurology causes the right behaviour what they believe makes no difference. The belief, one might say, floats along like an extra that’s caused by the neurology. But the beliefs don’t have to be true for the neurology to be adaptive. If the neurology causes false beliefs but causes the right actions it makes no difference whatsoever.
So, if you take a given belief on the part of one of these creatures and ask “What is the probability given that naturalism and evolution and materialism that the belief is true?” It’s got to be fairly close to 50/50, it is likely to be true as false, or it likely to be false as true. If that is the case then the probability that their cognitive faculties are reliable, which produces a substantial proportion of true beliefs that reliability requires, the probability that their faculties will be reliable will be very low” (1).
Prominent atheist philosopher Thomas Nagel likewise sees this while also giving some credit to Plantinga’s argument: “Evolutionary naturalism provides an account of our capacities that undermines their reliability, and in doing so undermines itself… I agree with Alvin Plantinga that… the application of evolutionary theory to the understanding of our own cognitive capacities should undermine, though it need not completely destroy, our confidence in them.
Mechanisms of belief formation that have selective advantage in the everyday struggle for existence do not warrant our confidence in the construction of theoretical accounts of the world as a whole. I think the evolutionary hypothesis would imply that though our cognitive capacities could be reliable, we do not have the kind of reason to rely on them that we ordinarily take ourselves to have using in them directly-as we do in science” (2).
This argument, should it follow, argues Plantinga,
“provides a defeater for your natural instinctive belief that your cognitive faculties are reliable… you get a reason not to hold that belief, a reason to reject it.”
Thus combining naturalism with evolution is self-defeating because the probability that humans would have reliable cognitive faculties as a result is so overwhelming low. The human cognitive faculty cannot be trusted to produce more true beliefs than false beliefs. Thus to assert that naturalistic evolution is true the naturalist also asserts that one has a low or unknown probability of being right.
If evolution is true, which the vast majority of naturalists believe to be the case, then ascribing truth to naturalism and evolution is dubious or inconsistent. Since the brain did not evolve to obtain truth, but only to increase one’s chances of survival, we cannot be confident that our own cognitive faculties leading us to conclude in atheism are reliable.