I never understood why it took so long to come up with this

One thing I have never understood about the theory of evolution, even back when I used to believe in it with little question, is how it is supposed that homo sapien existed for so long without making the basic discoveries that lead to permanent civilization on relatively recently. Anthropology is not a hard science--not even close--but I have yet to see any good explanation for why our ancestors suddenly learned the basics of agriculture out of nowhere. Who really believes that out of an alleged two hundred some thousand years of our species' existence, only "recently" did people get the bright idea to try to create their own reliable food supplies? For people who have to struggle daily to get food, it would be a no-brainer to realize that it would be really convenient if they could figure out a way to get the food to grow around them instead of hunting and gathering.

Chalk it up to simply assuming that our ancestors were all but too stupid to function?