We scientists have fantasies of being uniquely qualified to make great discoveries. Alas, reality is cruel: most of us are replaceable. For the vast majority of scientific contributions, if scientist X hadn't achieved it that year, scientist Y would have achieved the same result or something very similar soon thereafter.

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.

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

All of our current environmental problems are unanticipated harmful consequences of our existing technology. There is no basis for believing that technology will miraculously stop causing new and unanticipated problems while it is solving the problems that it previously produced.

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.

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.