Jared M. Diamond '62-'65 delivered a lecture in a packed Sanders Theatre yesterday afternoon on the reasons why humans on different continents have had such different evolutionary histories.

"This is the most interesting, most important question of human history," Diamond said. "Finding the answer to this inherently simple question is difficult."

He cited the Indian subcontinents and New Guinea as being very diverse, each with thousands of different languages. In contrast, in places like tropical southeast Asia, people speak very similar languages and look very similar as well, he said.

Diamond, author of the Pulitzer Prize-winning Guns, Germs, and Steel: The Fates of Human Societies, said the human population has homogenized because of changes in lifestyle that he called "agricultural expansion."

He noted that originally, many cultures were primarily hunter-gatherers who were mobile and would shift their camps according to the changing seasons and food supply.

Populations settled down, he said, when they were able to live in villages where they had their own continual food supply through farming. This caused large groups to stay in the same places for long periods of time. Because they did not migrate, the groups did not diversify.

Diamond said the main factor behind the evolution of different regions at different rates was the domestication of various animals and crops.

Diamond explained the differences in evolution on different continents in terms of their geography. He said that because the continents were stretched out on different axes, migration was different on each one.

"This orientation of the axes has had a huge effect on human history," he said. "The result is that crops and livestock domesticated in one part of Eurasia quickly spread to the rest of that continent."