Although it might not seem that way, judging from the images of war and pain that are so relentlessly beamed into our eyes each day, Steven Pinker argues that humans have actually become far less violent in recent times.
In a long but enthralling essay from 2007, he offers several explanations, philosophical and biological, for this pattern of progress. One of my favorite tidbits, offered by philosopher Peter Singer:
Evolution bequeathed people a small kernel of empathy, which by default they apply only within a narrow circle of friends and relations. Over the millennia, people’s moral circles have expanded to encompass larger and larger polities: the clan, the tribe, the nation, both sexes, other races, and even animals. The circle may have been pushed outward by expanding networks of reciprocity, à la Wright, but it might also be inflated by the inexorable logic of the golden rule: The more one knows and thinks about other living things, the harder it is to privilege one’s own interests over theirs.