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.

Eurasia ended up with the most domesticated animal species in part because it's the world's largest land mass and offered the most wild species to begin with.

All recognized famous inventors had capable predecessors and successors and made their improvements at a time when society was capable of using their product.

To dismiss the current extinction wave on the grounds that extinctions are normal events is like ignoring a genocidal massacre on the grounds that every human is bound to die at some time anyway.

Although native Africans domesticated some plants in the Sahel and in Ethiopia and in tropical West Africa, they acquired valuable domestic animals only later, from the north.

One way to explain the complexity and unpredictability of historical systems, despite their ultimate determinacy, is to note that long chains of causation may separate final effects from ultimate causes lying outside the domain of that field of science.

Our biggest threat is not an asteroid about to crash into us, something we can do nothing about. Instead, all the major threats facing us today are problems entirely of our own making. And since we made the problems, we can also solve the problems.