[1] The book presents a systematic discussion of ideas about the reasons for a culture making a transition by stages from egalitarian hunter-gatherer to hierarchically based states as population density increases.

Harris then discusses three 20th century innovations that explain this postponement of the catastrophe: the exploitation of petroleum, reliable contraceptives, and social changes in some cultures that make smaller families more desirable.

Harris notes that pigs were also taboo in Ancient Egypt and continue to be forbidden by Islam, suggesting that environmental rather than cultural factors were responsible for putting this food animal off-limits.

Desperation incurred during periods of drought might lead to the temptation to slaughter and eat the work animals for short-term survival; this would damage long-term prospects by destroying the means of production.

The necessity of labor-intensive projects such as irrigation, canals, and flood control dikes led to the development of strong, centralized, and despotic states to mobilize the needed manpower for construction.