Not until the beginning of the 20th century did Europe's urban populations finally become self-sustaining: before then, constant immigration of healthy peasants from the countryside was necessary to make up for the constant deaths of city dwellers from crowd diseases.

The single most important problem is our misguided focus on identifying the single most important problem!

In short, Europe’s colonization of Africa had nothing to do with differences between European and African peoples themselves, as white racists assume. Rather, it was due to accidents of geography and biogeography—in particular, to the continents’ different areas, axes, and suites of wild plant and animal species. That is, the different historical trajectories of Africa and Europe stem ultimately from differences in real estate.

I've always been interested in a lot of things, and a lot of things at the same time, and I always tried to explain them to myself. I ask a lot of questions.

Some people have much more pull than other people. But when I say that the public has ultimate responsibility, I'm not saying it in a moral sense. I'm just saying it in the sense of what is it that's really going to bring change.

In much of the rest of the world, rich people live in gated communities and drink bottled water. That's increasingly the case in Los Angeles where I come from. So that wealthy people in much of the world are insulated from the consequences of their actions.

[T]he values to which people cling most stubbornly under inappropriate conditions are those values that were previously the source of their greatest triumphs.