Even to this day, no native Australian animal species and only one plant species-the macadamia nut-have proved suitable for domestication. There still are no domestic kangaroos.

Why did human development proceed at such different rates on different continents for the last 13,000 years?

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.

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.

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!

Besides justifying the transfer of wealth to kleptocrats, institutionalized religion brings two other important benefits to centralized societies. First, shared ideology or religion helps solve the problem of how unrelated individuals are to live together without killing each other—by providing them with a bond not based on kinship. Second, it gives people a motive, other than genetic self-interest, for sacrificing their lives on behalf of others.

Recent discoveries about apes suggest, however, that a gorilla or common chimp stands at least as good a chance being murdered as the average human.