Pleistocene Brains

We hear it often in our field that modern humans have Pleistocene brains, brains suitably adapted to life in the savannas of Africa where our ancestors lived for thousands of years. It was this period of stability that solidified our Pleistocene mind and all those fun modules. But is there any real evidence for this supposed Pleistocene mind/brain? I mean, any biological evidence other than just-so stories constructed based on clinical experiments with modern humans. I really would appreciate a point in the right direction. It seems patently false that we have Pleistocene brains, and also to fly in the face of evolutionary theory, which indicates our biology is constantly adapting.