If you’re reading this article, you probably believe that Darwinian theory can shed light on human behaviour. And you probably think that this article is going to be an account of how the theory can explain yet more of the puzzling choices that humans make.I’m afraid not. This article is about a mystery that Darwinian theory has no ready answer for – at least not yet. It’s the mystery of our own reproductive choices. Darwinists have had a good deal of success convincing the general public that evolutionary theory can provide a means of gaining an understanding of their own behaviour. But we do this by weaving tissue-paper thin scraps of argument to hide the trunk and tusks of the beast in the room.Why are we producing so few children? At a superficial level, it isn’t puzzling. Each of us can give our own reasons for not producing a large number of children. For one thing, the kind of effort that would be necessary to raise a large family would leave us little effort to spare for learning about Darwinian theory and reading articles like this.But we Darwinists aren’t satisfied with superficial explanations so it’s time we discussed this. Today’s humans are able to access vastly more resources than our ancestors but we choose to devote them to purposes and activities that don’t enhance our fitness. Let’s face it; over the courser of our lives we invest a relatively small proportion of our time and effort producing and raising offspring or helping our close relatives raise theirs. Our ancestors, or at least most of them, were different; all of them had at least one child that survived to reproduce and many of them succeeded in raising large families in conditions that we can barely imagine surviving. According to one of the basic tenets of Darwin’s theory, we should have inherited the characteristics associated with this reproductive success. So what drove them to put so much effort into producing children and why haven’t we inherited it? Perhaps you have a theory. If so, please share it in the comments.The desire to mate seems to be an important driver of reproduction in many non-human animals. They aren’t motivated to produce offspring, just to pursue a set of behaviours that resulted in their ancestors’ genes being passed on to them. Human behaviour suggests we also experience desire to mate – but it is unlikely to be a very important driver of reproduction in humans. It doesn’t fit with our reproductive biology or our behaviour.Raising a human from conception to independence requires an enormous amount of parenting effort, more than can be provided by its mother alone or its mother and father working together (Hrdy 2009). Conceiving a child when support isn’t available would have been very detrimental to fitness. It follows from this that an uncontrollable desire to mate would have been strongly selected against, certainly in females. Every human population that has been studied has rules which establish responsibilities of parents and their supporters. These rules strongly influence who reproduces and when they reproduce. It’s impossible to know the extent to which our ancestors actually obeyed those rules. No doubt reproductive norm compliance varied from population-to-population, from time-to-time and from individual-to-individual but it’s likely that the most successful people were people like us – people who obeyed most of the rules most of the time.Our own experience of being human tells us that we’re motivated to pursue goals that seem within our reach and worthy of our effort. Except for the last few generations, our ancestors behaved as if they believed that raising children, as many as possible, was a worthy goal, a top priority. Most young adults today don’t believe this. Why not? What has changed?Well, many things have changed in the last couple of centuries and this has given social scientists scope to propose many possible “solutions” to the mysterious decline in human fertility. Here is a sample of the explanations offered:

  • There was no birth control technology then.
  • Women were oppressed then and were forced to have babies.
  • Religion taught that it was people’s duty to have many children.
  • They needed children to work on the farm and to support them in their old age.
  • They expected many of their children to die in infancy or childhood.

The problem with these explanations is that they’re uninformed by Darwinian theory and by the facts gathered by historians and anthropologists studying how people in high fertility populations really behave and what was really going on in different populations when their fertility began to decline. For more information about this, future articles will explore these topics:

  • How people in high fertility populations behave.
  • The transition to low fertility reproductive behaviour.

Amongst this information must be some clues that will help us to develop testable hypotheses to explain the revolution in human reproductive behaviour that has occurred in the last 200 years.We need hypotheses that are consistent with Darwinian theory. Those of us who take a Darwinian approach are able to appreciate an important thing about this revolution that most social scientists haven’t recognized: It results in humans starting to make extraordinarily altruistic choices while believing that we’re selfishly following our best interests. This altruism has had severe fitness costs and differences in the timing of a population’s change of mind about family size have shaped modern history. The new altruism first began to take hold in the people of France toward the end of the 18th century, more than two generations earlier than the rest of Europe (Coale and Watkins 1986). In the middle of the 18th century France’s prospects seemed similar to those of England. Her farms were becoming more efficient and her traders and artisans were finding new ways creating wealth. Her scientists and intellectuals were second to none. And her colonial empire included substantial parts of North America as well as the Caribbean, Africa and South Asia.By and large, life started to become easier for ordinary Europeans during the 18th century and, in the rest of Europe, people took advantage of this new prosperity. Families boasting of more than eight surviving children were not uncommon. But they were much less common in France. We know this in part because of the research that Jean-Baptiste Moheau (2000) did in his spare time while working as private secretary to the provincial governor in the port city of La Rochelle in South West France. He collected data on births, marriages and deaths and in 1778, when only 30, Moheau published a pamphlet entitled “Recherches et considérations sur la population de la France” (“Empirical Studies on the Population of France and Their Interpretation”). His work revealed that in parts of France fewer children were being born and more dying in infancy. He makes his feelings about this clear in his conclusion. He mostly blames women:“…rich women, for whom pleasure is the greatest interest and the sole occupation, are not the only ones who regard the propagation of the species as a dupery of olden times; already the fatal secrets unknown to any animal but man have penetrated in the countryside: nature gets cheated even in the villages.” The “secrets” he refers to are ways of achieving sexual pleasure without the risk of conceiving a child. He also criticises women who don’t breast-feed their babies as his data revealed that infants not fed by their own mothers suffered higher mortality. Moheau predicts that “if these licentious practices, if these homicidal tastes, spread further, they will be no less fatal to the State than the plagues that devastated it in the past.”To modern ears, Moheau sounds crazy but, in a way, he had a point, a point, which is amply demonstrated by what followed. The practises and tastes that he complained about did spread through France and, while the rest of Europe enjoyed a population boom, population growth in France stagnated. The industrial revolution was transforming people’s lives and throughout the 19th century as young people from the countryside flooded into the areas where they could get work in factories, mines and construction sites. First Britain and then other Northern European countries became manufacturing powerhouses with vast trading empires – but not France, where there were simply not that many people to employ in industry.

The numbers leaving Europe during the 18th, 19th and first half of the 20th century are staggering.

Many Europeans decided to travel further and colonize new territory, displacing and in some cases subjugating the peoples already living there. The numbers leaving Europe during the 18th, 19th and first half of the 20th century are staggering. It’s been estimated that over two million Spanish went to South and Central America. Nearly a million and a half Portuguese settled in Brazil. South America also became the new home of 1.8 million Austro-Hungarians and 3.7 million Italians. North America received 5 million immigrants from Germany, 3.6 from Poland, 2.7 from Scandinavia, 3.2 from the Austro-Hungary, 5 million from Italy and 2.2 million from Russia. Another 10 million Russians colonized Siberia and Central Asia. But the biggest stream of immigrants came from the two large English-speaking islands off the coast of Europe, Great Britain and Ireland. Thirteen and a half million went to North America and another three million went to southern African and Australia. The fertility and dispersal of people on these two islands goes a long way to explaining why English is now the language of business, diplomacy and science.The French people’s early adoption of the idea that it’s better to have small families meant that France contributed only a trickle to the river of European immigration. Most North Americans of French ancestry are descended from the few thousand French colonists who settled there in the 17th and 18th centuries.The great European population expansion (sans France) didn’t last long. By the end of the 19th century small families started to become common in other parts of Europe and, by the 1920s, fertility in many parts of Europe had dropped to the same low levels that we see today. And now, less than a hundred years later, the fertility of almost all human populations is as low as that of Europeans or falling rapidly.Why have humans stopped competing for fitness? It’s hardly scientific to say that we should stop worrying about why it’s happening and just congratulate our species for being sensible and realizing that failing to curb population growth will be our downfall. And besides, congratulations are hardly in order. As our production of offspring has waned, our production and consumption of many other things has rocketed. Over the last century, the populations that produced the fewest children consumed by far the largest chunk of the world’s resources.Low fertility alone isn’t going to protect the planet from human desecration but our species’ sudden abandonment of competition for fitness has had other effects. Only a hundred years ago, Europeans were sending their young men off to fight and die for the right of their leaders to claim territory for their nation. In demographic terms, it’s a reasonable thing to do. If populations are expanding, new territory is needed. Records show that most Europeans living at the time did see the First World War as reasonable. The population was still rising rapidly. Many couples had decided to limit the size of their family but there were a lot of reproductive age couples producing offspring. After the war, the idea of family limitation continued to spread and the number of reproductive age couples declined.Meanwhile, another idea began to spread among Europeans: that military might does not give one people the right to claim ownership of territory occupied by another people. They did fight another huge war and have had a few military skirmishes but the idea has now really taken hold. Most of today’s Europeans have trouble believing that their antecedents could have been so immoral. Most of us believe we must share the planet, not only with other humans but with other species too.Sharing the territory that we think of as “our own” is not so popular. A lot of Westerners are unhappy about people moving to their country from poorer, less secure parts of the world. These immigrants mostly come from places where the human population had boomed in the 20th century. Like Europeans a few generations earlier, the children of that boom are dispersing and attempting to colonize new territory. Luckily for them, Western countries created many unfilled niches for them to occupy. Despite the brief and tiny “baby boom” that some populations experienced in the 1950s and early 60s, Western couples produced so few children that the economies of many countries in Europe and North American grew much faster than the population. As a result, there were potentially many more jobs than native Westerners to fill them. Some of the immigrants have been highly educated or skilled but many weren’t and they eagerly took unskilled jobs that natives were unwilling to do for the wages being offered.As they enhance the lifestyle of the natives of their new country, immigrants enhance their own fitness, raising families in the West and often setting aside part of their earnings to help support their relatives back home. This fitness boost has only been temporary, however. Most immigrants to the West arrive with, or soon adopt, the belief that it’s prudent to only have a small number of children. And in their countries of origin, fertility is now low or falling rapidly. According to United Nations estimates (http://esa.un.org/wpp/unpp/panel_indicators.htm), fertility in the Philippines is now at less than three children per women, down from over seven in the 1960s. Fertility in Mexico and Bangladesh, which peaked at nearly seven in the late 1970s, has now plummeted to just over two. Only in some parts of Sub-Saharan Africa is fertility remaining high.Without a doubt, life is more comfortable for people who have smaller families. And once people no longer compete for fitness they can strive for sporting or artistic accolades or higher degrees, good jobs and getting papers into Science or Nature. Or they can just take it easy and watch TV. Women need no longer spend the prime years of their lives being pregnant and lactating. Marriage no longer needs to be a longterm reproductive partnership. It can just be the joining together of two people who get pleasure out of being together. If it stops being pleasurable, divorce is possible. And those who decide to have a couple of kids can afford to make their childhood fun and to educate them to increase their chances of having a comfortable and interesting life too.A person not trained in Darwinian theory might think that the real mystery is why humans took so long to work out that it’s a good idea to have fewer children – or no children at all if times are tough. For Darwinists it’s no mystery. People in the past did get the idea – after all it’s not a hard idea to get. But for the most part, the people who chose that easier life are not our ancestors. Our ancestors were mostly the ones who kept on reproducing and out-competed the ones who had few or no children.Something kept our ancestors’ noses to the fitness grindstone and whatever it is either didn’t get passed on to us or is ineffective in today’s environment. Because of this, human life today is very different from that of our ancestors and it is continuing to change rapidly. If evolutionary theory is be of real help in understanding our present behaviour and what our future might hold, we need to get a grip on what it is.So what is it? Please place your ideas below. Or, if you think the question should continue to be ignored, tell us why.

Literature cited

Coale, A. J. and S. C. Watkins (1986). The Decline of Fertility in Europe. Princeton, N.J., Princeton University Press.Hrdy, S. B. (2009). Mothers and Others: The evolutionary origins of mutual understanding. Cambridge, MA, Harvard University Press.Moheau, J.-B. (2000). "Jean-Baptiste Moheau on the moral causes of diminished fertility." Population and Development Review 26(4): 821-826.