Duh! Scientists once again chase the obvious. The 'civilized' nature of man in this generation is a far cry from what was considered 'civilized' in all prior generations. It was only in the 1970's that corporal punishment started loosing favor as the discipline of choice for children. Mass deprivation and killing were common, legitimate means of enforcing government rule in centuries past, and is still practiced in some countries today.
In this country many of us struggle to comprehend how some peoples of this time and before can be so brutal. But, violence has always bred violence. This is nothing new. What is being overlooked is the growing stratification of understanding. Violence is so alien to some people these days that it no longer has meaning is the sense that violence is something "sane" people are capable of.