By 'reason' I mean both the process of coming to logical conclusions from given premises, and the correct conclusions logically drawn from the true premises of reality.

People claim that because un consciously-worked-out intuitions are often surprisingly correct, reason is insufficient to explain everything. They decide that there is something mysterious above reason. As if reason was a fanciful human invention and not the way things are.

But the very physical connections made in human [and animal] brains must obey the laws of physics, which can be expressed entirely using mathematics, the most logical and reasonable discipline to exist. Furthermore, since a lack of reason [substitute logic, order] results in chaos not condusive to life but only to entropy, it makes sense that natural selection favors the survival of creatures whose intuitions and unconscious brain activity are reasonable. This seems painfully obvious. If the brain stopped sending logical messages to the heart, or the heart stopped reading messages logically, the brain and the heart would both destruct in very short order.

Much closer to the level of conscious deductive reasoning than the activity of internal organs, the intuitive conclusions that humans often jump to are similarly helpful to the survival of the human when correct, and just as likely to have evolved to follow logical rules, by which they would be most certain to be usually correct.

[I admit that this is not a original idea, but it is one I came up with in a rough form quite a long time ago, I think when I was about ten, and I am very happy to be able to finally explain it.]