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.

Twelve thousand years ago, everybody on earth was a hunter-gatherer; now almost all of us are farmers or else are fed by farmers. The spread of farming from those few sites of origin usually did not occur as a result of the hunter-gatherers' elsewhere adopting farming; hunter-gatherers tend to be conservative.... Instead, farming spread mainly through farmers' outbreeding hunters, developing more potent technology, and then killing the hunters or driving them off of all lands suitable for agriculture.

What did the last Easter Islander say as he chopped down the last tree? The Easter Islanders didnt have anthropologists.

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.

The rate of human invention is faster, and the rate of cultural loss is slower, in areas occupied by many competing societies with many individuals and in contact with societies elsewhere.

Rhino-mounted Bantu shock troops could have overthrown the Roman Empire. It never happened.

Perhaps our greatest distinction as a species is our capacity, unique among animals, to make counter-evolutionary choices.