"White blood cells and other cells of ours actively seek out and kill foreign microbes. The specific antibodies that we gradually build up against a particular microbe infecting us make us less likely to get reinfected once we become cured. As we all know from experience, there are some illnesses, such as flu and the common cold, to which our resistance is only temporary; we can eventually contract the illness again. Against other illnesses, though—including measles, mumps, rubella, pertussis, and the now defeated smallpox — our antibodies stimulated by one infection confer lifelong immunity. That's the principle of vaccination: to stimulate our antibody production without our having to go through the actual experience of the disease, by inoculating us with a dead or weakened strain of microbe."

“Just as strawberries are adapted to birds, so acorns are adapted to squirrels, mangos to bats, and some sedges to ants. That fulfills part of our definition of plant domestication, as the genetic modification of an ancestral plant in ways that make it more useful to consumers. But no one would seriously describe this evolutionary process as domestication, because birds and bats and other animal consumers don't fulfill the other part of the definition: they don't consciously grow plants.”

“If the Easter Islanders couldn't solve their milder local problems in the past, how can the modern world hope to solve its big global problems? People who get depressed at such thoughts often then ask me, “Jared, are you optimistic or pessimistic about the world’s future?” I answer, “I am a cautious optimist.” By that, I mean that, on the one hand, I acknowledge the seriousness of the problems facing us. If we don’t make a determined effort to solve them, and if we don’t succeed at that effort, the world as a whole within the next few decades will face a declining standard of living, or perhaps something worse. That’s the reason why I decided to devote most of my career efforts at this stage of my life to convincing people that our problems have to be taken seriously and won’t go away otherwise. On the other hand, we shall be able to solve our problems – if we choose to do so.”

“Because we are the cause of our environmental problems, we are the ones in control of them, and we can choose or not choose to stop causing them and start solving them. The future is up for grabs, lying in our own hands. We don’t need new technologies to solve our problems; while new technologies can make some contribution, for the most part we "just" need the political will to apply solutions already available.”

“As we shall see in this book's chapters, traditional societies are far more diverse in many of their cultural practices than are modern industrial societies. Yet psychologists base most of their generalizations about human nature on studies of our own narrow and atypical slice of human diversity. That is, as social scientists Joseph Henrich, Steven Heine, and Ara Norenzayan express it, most of our understanding of human psychology is based on subjects who may be described by the acronym WEIRD: from Western, educated, industrialized, rich, and democratic societies. Hence if we wish to generalize about human nature, we need to broaden greatly our study sample from the usual WEIRD subjects to the whole range of traditional societies.”

“The societies to which most readers of this book belong represent a narrow slice of human cultural diversity. Societies from that slice achieved world dominance not because of a general superiority, but for specific reasons: their technological, political, and military advantages derived from their early origins of agriculture, due in turn to their productive local wild domesticable plant and animal species. Despite those particular advantages, modern industrial societies didn’t also develop superior approaches to raising children, treating the elderly, settling disputes, avoiding non-communicable diseases, and other societal problems. Thousands of traditional societies developed a wide array of different approaches to those problems.”

“My views may seem to ignore a moral imperative that businesses should follow virtuous principles, whether or not it is most profitable for them to do so. Instead I prefer to recognize that, throughout human history, government regulation has arisen precisely because it was found to be necessary for the enforcement of moral principles. Invocation of moral principles is a necessary first step for eliciting virtuous behavior, but that alone is not a sufficient step.”