I think there's been a lot of neurological evolution since the Pleistocene.
We once lived as hunter-gatherers, in small bands, in a hostile world and in competition with neighboring bands.
At that time everyone was a Republican, so to speak -- hypervigilant, regimented, nervous, neophobic, xenophobic, and with a fierce tribal loyalty. Moral consideration was strictly in-house and did not extend beyond the tribe.
With the agricultural revolution and advent of settled communities selective pressures changed. Limbic neurology began to diminish. Human psychology started to become more cosmopolitan, the average size of the Right amygdala began to diminish and the anterior cingulate nucleus grew.
Today our species exhibits a wide neurological spectrum. Our hunter's hypervigilance and nervousness is now called ADHD, and is no longer selective, and the atavistic, tribal psychology of the far right works at cross purposes to the calmer, more flexible, cosmopolitan psychology of those on the far left. The anatomical and physiologic differences are usually clearly identifiable on CTs and fMRIs.
Many of us are born with brains little different from our troglodyte ancestors.