THE GERMAN PUBLIC was recently shocked to learn that 30% of "their" women are childless -- the highest proportion of any country in the world. And this is not a result of infertility; it's intentional childlessness.
Demographers are intrigued. German nationalists, aghast. Religious fundamentalists, distressed at the indication that large numbers of women are using birth control.
And evolutionary biologists (including me) are asked, "How can this be?" If reproduction is perhaps the fundamental imperative of natural selection, of our genetic heritage, isn't it curious -- indeed, counterintuitive -- that people choose, and in such large numbers, to refrain from participating in life's most pressing event?
The answer is that intentional childlessness is indeed curious -- but in no way surprising. It is also illuminating, because it sheds light on what is perhaps the most notable hallmark of the human species: the ability to say no -- not just to a bad idea, an illegal order or a wayward pet but to our own genes.
When it comes to human behavior, there are actually very few genetic dictates. Our hearts insist on beating, our lungs breathing, our kidneys filtering and so forth, but these internal-organ functions are hardly "behavior" in a meaningful sense. As for more complex activities, evolution whispers within us. It does not shout orders.
People are inclined to eat when hungry, sleep when tired and have sex when aroused. But in most cases, we remain capable of declining, endowed as we are with that old bugaboo, free will. Moreover, when people indulge their biologically based inclinations, nearly always it is to satisfy an immediate itch, whose existence is itself an evolved strategy leading to some naturally selected payoff. A person doesn't typically eat, for example, with the goal of meeting her metabolic needs but to satisfy her hunger, which is a benevolent evolutionary trick that induces the food-deprived to help out their metabolism.
For more than 99.99% of their evolutionary history, humans haven't had the luxury of deciding whether to reproduce: simply engaging in sex took care of that, just as eating solved the problem of nutrition. But then something quite wonderful arrived on the scene: birth control. Because of it, women (and men) can exercise choice and, if they wish, save themselves the pain, risk and inconvenience of childbearing and child-rearing, indulging themselves rather than their genetic posterity.
Add to this another important observation from nature. Behavioral ecologists distinguish between what are known as "r" and "K" strategies among living things. Thus, "r" strategists -- such as mice and rabbits -- breed early and often, producing large numbers of offspring that suffer high mortality. "K" types -- such as elephants and whales -- breed later and relatively rarely, producing fewer offspring (with lower mortality) and investing more in each. Neither elephants nor whales send their children to college, although they indulge in the animal equivalent.
Pretechnological human beings are comparatively "r" in their reproductive style. But with improved socioeconomic conditions -- especially, better educational and vocational opportunities for women -- comes the demographic transition, whereby "r" gives way to "K," and infant mortality plummets along with birthrate. There also arises a tendency to take especially good care of the fewer children one produces, as well as a greater inclination to look out for No. 1, sometimes -- horror of horrors! -- by producing no children at all.
It happens over and over, from Nigeria to Nicaragua. Even the already low birthrates in developed countries become lower still when each child is expected to be outfitted with an iPod and yoga lessons, not to mention a personal trainer. It is notable that child-wariness is not only characteristic of highly developed Germany (and northern Europe as a whole), but that it rises from 30% to more than 40% among German women who are college graduates.
When it comes to our behavior, evolution is clearly influential. Of this there can be no doubt. But only rarely is it determinative, even when something as deeply biological as reproduction is concerned. Indeed, the trend toward childlessness is neither particularly German nor strangely "un-biological" but profoundly human.