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.

Throughout history, adultery has had few rivals as a cause of murder and human misery. The reason we tend to resemble our mates is that many of us are looking for someone who reminds us of our parent or sibling of the opposite sex, who in turn resembles us.

Two types of choices seem to me to have been crucial in tipping the outcomes [of the various societies' histories] towards success or failure: long-term planning and willingness to reconsider core values. On reflection we can also recognize the crucial role of these same two choices for the outcomes of our individual lives.

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

The United States has long thought of itself as the land of infinite plenty, and historically we did have abundant resources. But now we are gradually exhausting our fisheries, our topsoil, our water. On top of that, we're coming to the end of world resources.

The history of interactions among disparate peoples is what shaped the modern world through conquest, epidemics and genocide. Those collisions created reverberations that have still not died down after many centuries, and that are actively continuing in some of the world's most troubled areas.

The southward advance of native African farmers with Central African crops halted in Natal, beyond which Central African crops couldn't grow - with enormous consequences for the recent history of South Africa.