We really are creatures of a violent world, biologically speaking - watching violence and learning about it is one of our cognitive drives.

As women are empowered, violence can come down, for a number of reasons. By all measures, men are the more violent gender.

For all the tribulations in our lives, for all the troubles that remain in the world, the decline of violence is an accomplishment that we can savor - and an impetus to cherish the forces of civilization and enlightenment that made it possible.

Of course, genes can't pull the levers of our behavior directly. But they affect the wiring and workings of the brain, and the brain is the seat of our drives, temperaments and patterns of thought.

I think that communism was a major force for violence for more than 100 years, because it was built into its ideology - that progress comes through class struggle, often violent.

So holding many factors constant, we find that living in a civilization reduces one’s chances of being a victim of violence fivefold.