-Except that during the Pleistocene humans rarely lived past their mid-20s. What we call adolescence was the period when the most babies were produced and the most fighting was done.

Humans lived in tribes. Tribes which had clear advantages in communicating, cooperating, memorizing, conceptualizing, anticipating, and using complex technologies would prevail against other tribes in conflict.

The winners would typically dispatch all the males and incorporate the females, a process described in detail in the old testament.

This unnatural form of group selection caused our brains to grow to an unnatural and unsustainable size. They are thus fragile, damage- and defect-prone, and energy-hungry; and they begin to deteriorate soon after reaching maturity.

Disclaimer: amateur posters here at physorg rarely know what they are talking about, unless of course what they are saying makes perfect sense.