Much of human history has consisted of unequal conflicts between the haves and the have-nots.

With the rise of chiefdoms around 7,500 years ago, people had to learn, for the first time in history, how to encounter strangers regularly without attempting to kill them.

African cavalry mounted on rhinos or hippos would have made mincemeat of European cavalry mounted on horses. But it couldnt happen.

Twenty years ago, you might have been pessimistic and said there's no hope. But these days, some of our very biggest companies are acting remarkably cleanly. And in some cases, although not all cases, the CEOs are the driving forces behind that.

Bird taxonomy is a difficult field because of the severe anatomical constraints imposed by flight. There are only so many ways to design a bird capable, say, of catching insects in mid-air, with the result that birds of similar habitats tend to have very similar anatomies, whatever their ancestry. For example, American vultures look and behave much like Old World vultures, but biologists have come to realize that the former are related to storks, the latter to hawks, and that their resemblances result from their common lifestyle.

Thousands of years ago, humans domesticated every possible large wild mammal species fulfilling all those criteria and worth domesticating, with the result that there have been no valuable additions of domestic animals in recent times, despite the efforts of modern science.

Why did human development proceed at such different rates on different continents for the last 13,000 years?