Despite tens or hundreds of thousands of years of very strong Natural Selection, wildebeest do not arrive at the Mara River with a genetically determined brain mechanism or module that helps (much) to keep them from being eaten by the crocodiles that live in the river. Most of the wildebeest that try to cross the Mara in the annual migration have never seen a croc, or a river, before in their lives, or have encountered this situation only once. This would be a very good situation in which to evolved such a mechanism.
Where is evolutionary psychology when you really need it?