10000 years ago was when we started consuming them en masse. We ate some grains before then, but natural selection doesn't work unless it is enough to affect ability to reproduce. And since grains are biologically designed to harm those who eat them, it would likely take a massive overhall of the human digestive system, which didn't really happen. I think the grains assumed that we would be smart enough to realize that grains were bad for us and stop eating them...
There is Cordain's original grains article. It mentions the agricultural revolution and has citations for most of its statements.
Stabbing conventional wisdom in its face.
Anyone who wants to talk nutrition should PM me!