Recent discoveries about apes suggest, however, that a gorilla or common chimp stands at least as good a chance being murdered as the average human.

History followed different courses for different peoples because of differences among peoples' environments, not because of biological differences among peoples themselves

No government is here forever. And there are other forces - the most potent force in our society, in fact, big business - doing good for the environment.

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

We study the injustices of history for the same reason that we study genocide, and for the same reason that psychologists study the minds of murderers and rapists... to understand how those evil things came about.

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.

Take air quality in the United States today: It's about 30 percent better than it was 25 years ago, even though there are now more people driving more cars.