If evolution is true, how can you trust your monkey brain?

Several times now commentors have put forward a challenge that I found rather novel (or, rather, it wasn’t among the many witnessing tricks I had learned at the evangelical school I went to for 10 years). I’m writing this post so that when I am asked this question in the future I can just direct the commentor to this post rather than typing it all out again.  The question goes something like this:

If you believe that humans evolved by chance, how can you really trust your brain and your ability to rationalize? What if your brain evolved to trick you? What if your brain is flawed? If our brains evolved from the brains of more primitive animals, if we have the brains of monkeys, why should we put faith in our intellect?

We can put “faith” in our ability to reason because we can test our brain’s ability to reason and see the results. We learn from using our brains how reliable they are. Take the example of physics. You have a physics, say Newton, sitting around and using his brain to reason. He comes up with a theory and an equation, using his brain coupled with basic observations of the physical world: F = ma (force equals mass times acceleration). It seems to make logical sense to him, but how can he find out if it is true? He can test it. And then thousands of scientists after him can test it. They all found out that F does equal ma, that his reasoning was correct.

A second clause of this argument is basically the “brain in a vat” argument, also known as, “What if the Matrix is real?” What if our brains are engaging in some sort of mass delusion? How can we confirm that our brains are reliably judging the world and not just being tricked by aliens or demons? How can we tell that our brains are perceiving the real world and not a false construction?

It’s basically a moot question. Now, either the brain is indeed capable of making such accurate predictions about the physical world as F=ma, or we’re all living in some sort of delusion where F does not equal ma, but we somehow still see it as a correct equation. In that case it doesn’t really matter, because we are all engaging in a shared delusion. If all of our observations of the physical world are incorrect but exactly the same then we will never have a way to discover the “truth,” and thus the delusion, if perfectly shared, becomes a sort of truth itself – or at least the only truth we can ascertain.

In my opinion, the weakest point of this argument is the false assumption that evolution could somehow result in a brain of a large and complex animal that lacks the ability to reason accurately. What would be the evolutionary benefit to having such a faulty brain? How could an animal that lacks the ability to rationalize be able to evolve to the point that humans and other primates have reached? Reason is key to survival. A reasoning brain allows an animal to observe its environment and respond to it correctly.

Let’s say we have a primitive primate whose brain causes him to come to the wrong conclusions about the physical world. He sees a large cat coming at him and him brain tricks it into thinking it is a harmless mouse. That monkey is dead. Dead monkeys can’t pass on their genes. He sees a stagnant pool of water and his brain tricks it into thinking it is a crystal clear stream. That monkey gets a parasite and is dead. Let’s make it simple and say that the monkey’s brain is just really bad at connecting two events. Let’s say he sees his brother get caught and eaten by a big cat. If the next time he sees the same type of cat and doesn’t make the logical connection that “big cats equal dead monkeys” and thus doesn’t run away, he is going to be eaten. Dead monkey. To make it even more simple, let’s say you have a monkey whose brain doesn’t cause a grand delusion, but is just not very good at logically analyzing its situation in relation to the physical world. Let’s say the monkey has poor depth perception. He looks at the natural world and is unable to accurately reach conclusions about it. He is sitting in a tree and sees a piece of big fruit in another tree nearby. He looks out, but because of his brain that lacks the cognitive ability to perceive depth (a basic form of reasoning), he thinks that the branch of that other tree over there isn’t really that far away, so it makes a jump for it. But it was very far away indeed, and now: splat. Dead monkey.

Here I go using my rational brain again, but it doesn’t make logical sense for a complex animal to have evolved a brain that is unable to reason. But don’t worry, I can trust my brain on this because it hasn’t lead me astray so far. I’ve been doing a really good job of observing my surroundings and making inferences. I’m able to reason that rotten meat could make me sick, so I don’t eat it. I’m able to reason that it wouldn’t be a very good idea to step out in front of that speeding bus, so I wait for it to pass before crossing the street. I’m able to reason that five apples is more than two apples. I’m able to reason that five apples plus two apples equals seven apples. Every time I draw a conclusion or make a decision that conforms with reality, I’m demonstrating the fact that I have a brain capable of reason and rationality, even if it is just a monkey brain.