Perhaps the most significant development of all was the genetic mutation that appeared in certain species of grass coincident with the end of the last ice-age around 11,700 years ago. This mutation caused the seed of the grass to detach far more readily than hitherto, and enabled winnowing to occur. As we humans rapidly became dependent on various species of grass (wheat, barley, rice, etc.) for the bulk of our calories, it seems reasonable to hypothesize that had it not been for the genetic alterations occurring in grass, we'd have found it far more difficult to settle down into a pastoral mode of existence. And of course without grass to out-compete forests, there wouldn't have been the relatively open lands available to cultivate in the first place. We are, in a great many senses, children of grass far more than we're children of climate alone.