Debates about evolutionary psychology are extraordinarily difficult because two major turning points have occurred within an astonishingly short period of history. Each of these turning points brought about a fundamental change in the rules governing human behavior.
As a result, all theories, explanations, and hypotheses are subject to considerable uncertainty, and many questions remain unanswered. This is probably also why evolutionary psychology has no explanation for the current decline in birth rates. Have people begun acting against biological instincts that evolved over hundreds of thousands of years? How is that possible? Or are they following those instincts now, having acted against them until recently? Or is something entirely different happening?
This also means that drawing conclusions from contemporary human behavior is both difficult and uncertain. A reasonable approach is to identify a general principle that applies across species and then illustrate it for readers using human examples. At first glance, this may seem like an insignificant methodological distinction, but it is fundamental.
The first turning point occurred at somewhat different times and in somewhat different ways across European countries. Broadly speaking, however, we can place it between the second half of the eighteenth century and the middle of the twentieth century.
As late as 1700, fewer than half of Europe’s inhabitants passed their genes on to the next generation (the proportion was somewhat higher among women and somewhat lower among men). By 1900, that figure had risen to two-thirds of the population, and by around 1950, it exceeded 80 percent.
This represents a radical change in patterns of selection. It also means that certain strategies that had previously been unviable suddenly became advantageous, while others lost their value. Two factors drove this transformation: declining child mortality and the fact that, as populations grew wealthier, more people could afford to marry.
The second turning point came in the 1980s. Much attention has been devoted to female contraception, which arrived a generation earlier, but its significance has been greatly exaggerated. Very few young women experience such an overwhelmingly powerful sex drive that they cannot restrain themselves and end up conceiving a child.
The 1980s brought a change that directly affected male behavior: genetic paternity testing and the effective enforcement of child support obligations through the courts.
This completely overturned a pattern that had prevailed for thousands of years, under which having a child imposed an enormous burden on a woman, while a man could scatter his seed without a care in the world. If the man was wealthy, he would often provide for the mother of his illegitimate child, but he was under no obligation to do so. And he certainly would not provide for her to an extent that interfered with his own plans for life.
Suddenly, paternity could be established beyond doubt, and a man could be compelled to pay child support proportionate to his income—an amount substantial enough to be felt even by a wealthy man—for nearly thirty years.
Suddenly, male sexual restraint made sense. The most desirable men began to disappear from the dating pool, and some women responded by adopting the strategy of “better no man than a lousy one.”
Once remaining childless becomes an acceptable alternative, people begin to view relationships differently, build their lives in different ways, cultivate different skills, and so on.
Unlike animals, human beings are not governed directly by their genes but by institutions—that is, established customs and practices. These can change very rapidly. As a result, prevailing patterns of behavior can become substantially different within just one or two generations.
An institution cannot contradict biological predispositions, but the same predisposition can be expressed through very different institutions. This is also why it is so difficult for us to understand our ancestors who lived before the Industrial Revolution.