Jared Diamond

Those numbers may not sound like a big deal until one reflects that average global temperatures were "only" 5 degrees cooler at the height of the last Ice Age.

In fact, one of the main lesson to be learned from the collapses of the Maya, Anasazi, Easter Islanders, and those other past societies (as well as from the recent collapse of the Soviet Union) is that a society's steep decline may begin only a decade or two after the society reaches its peak numbers, wealth, and power. [...] The reason is simple: maximum population, wealth, resource consumption, and waste production mean maximum environmental impact, approaching the limit where impact outstrips resources. On reflection, it's no surprise that declines of societies tend to follow swiftly on their peaks.

Thus, because we are rapidly advancing along this non-sustainable course, the world's environmental problems will get resolved, in one way or another, within the lifetimes of the children and young adults alive today The only question is whether they will become resolved in pleasant ways of our own choice, or in unpleasant ways not of our choice, such as warfare, genocide, starvation, disease epidemics, and collapses of societies. While all of those grim phenomena have been endemic to humanity throughout our history, their frequency increases with environmental degradation, population pressure, and the resulting poverty and political instability.

[..] the values to which people cling most stubbornly under inappropriate conditions are those values that were previously the source of their greatest triumphs.

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.

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.

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!"

Perhaps we could benefit by selectively adopting some of those traditional practices. Some of us already do so, with demonstrated benefits to our health and happiness. In some respects we moderns are misfits; our bodies and our practices now face conditions different from those under which they evolved, and to which they became adapted. But we should also not go to the opposite extreme of romanticizing the past and longing for simpler times. Many traditional practices are ones that we can consider ourselves blessed to have discarded — such as infanticide, abandoning or killing elderly people, facing periodic risk of starvation, being at heightened risk from environmental dangers and infectious diseases, often seeing one’s children die, and living in constant fear of being attacked. Traditional societies may not only suggest to us some better living practices, but may also help us appreciate some advantages of our own society that we take for granted.

Though seemingly remote from human sexuality, shorebird sexuality is instructive because it illustrates the main message of this book: a species’ sexuality is molded by other aspects of the species’ biology. It’s easier for us to acknowledge this conclusion about shorebirds, to which we don’t apply moral standards, than about ourselves.

Behavior evolves through natural selection, just as anatomy does. Hence if sex is enjoyable, natural selection must have been responsible for that outcome.

Our sex is ultimately laid down by our genes.

In particular, while natural selection favors both males and females that leave many offspring, the best strategy for doing so may be different for fathers and mothers. That generates a built-in conflict between the parents, a conclusion that all too many humans don’t need scientists to reveal to them. We make jokes about the battle of the sexes, but the battle is neither a joke nor an aberrant accident of how individual fathers or mothers behave on particular occasions. It is indeed perfectly true that behavior that is in a male’s genetic interests may not necessarily be in the interests of his female co-parent, and vice versa. That cruel fact is one of the fundamental causes of human misery.