“Science is often misrepresented as ‘the body of knowledge acquired by performing replicated controlled experiments in the laboratory.’ Actually, science is something broader: the acquisition of reliable knowledge about the world.”

“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.”

“People often ask, "What is the single most important environmental population problem facing the world today?" A flip answer would be, "The single most important problem is our misguided focus on identifying the single most important problem!”

“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.”

“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."[Why Societies Collapse, ABC Local, July 17, 2003]”

“It's striking that Native Americans evolved no devastating epidemic diseases to give to Europeans in return for the many devastating epidemic diseases that Indians received from the Old World.”

“(On the beginning of the mid-1990s' genocidal war in Rwanda:)Within six weeks, an estimated 800,000 Tutsi, representing about three-quarters of the Tutsi then remaining in Rwanda, or 11% of Rwanda's total population, had been killed.”