I found this question on Quora.
Here’s my answer:
No animals are rational. Animals that are capable of reasoning don’t use their reason most of the time. This includes humans. Humans rarely weigh all the choices they could make and then make the choice that leads to the best outcome.
And this is good.
If animals and people reasoned about choices every time they could, they would be much too slow. When a monkey sees a leopard, it doesn’t look at all the paths it could take to escape. It climbs the nearest tree. It probably doesn’t even check to see if that tree has a python in it.
If monkeys weighed all of their options, all of them would soon be dead. Instead several monkeys will pick several different options, and most of those monkeys turn out fine.
Many humans have managed to stake out a much cushier lifestyle than animals so that they have more time to make rational choices. They are more rational than monkeys. But we still rely on our instincts for much of what we do. Which is great if you can find the right balance.