This is the law of nature: the more well-fed and healthy living beings are, the more actively they produce offspring. There is only one exception — a person: wealthier people are less eager to procreate. How to explain this phenomenon?
It took humanity several thousand years to reach a population of 1 billion. This was at the beginning of the 8th century. And in just over two hundred years, the world’s population has grown to XNUMX billion. And this is absolutely logical, evolutionary biologists and anthropologists are sure.
Scientists are worried about something completely different. Population growth is much slower than it should be according to their calculations. And above all — in the most developed countries. From an evolutionary standpoint, this is a paradox.
The better the living conditions, the more readily the creatures that are lucky enough to get into these conditions reproduce.
This is true for animals and plants, this law is confirmed by the development of patriarchal human communities and the example of modern developing countries. However, in developed countries, everything is exactly the opposite: the higher the standard of living, the less willingly people have children. Such a change in the pattern of fertility is called a demographic shift and still has no scientific explanation.
Quantity or quality?
Evolutionary theory teaches that the transmission of genes to subsequent generations is the main task of any living being. And a person is no exception, no matter how much he is offended by such a simplified approach to his complex person. But the demographic shift is clearly contrary to evolution. After all, the fewer children, the lower the chances of sending your precious genes into the future. Or not?
In 2008, anthropologist David Lawson conducted a study in which about 14 British children took part.1. And he found that offspring from large families in many respects were inferior to their peers from families where only 1-2 children were brought up. This concerned both the attention paid by parents and the funds that the family invested in the education and physical development of children. Finally, children from small families, on average, turned out to be even taller than those from large families.
Perhaps this is the non-obvious, but no less significant evolutionary advantage of the demographic shift?
By investing more in fewer children, we kind of guarantee the transfer of genes. Then we have to assume that a larger number of less well-to-do heirs does not provide such a guarantee. To test this idea, a significant data set is required that takes into account the level of wealth, education and number of children in a large number of families over many generations.
David Lawson is lucky. Such data was found in Sweden, where, since the middle of the 14th century, information about XNUMX thousand natives of the city of Uppsala and their descendants has been tracked. Lawson and colleagues analyzed them in the most careful way — and were forced to admit that the hunch about the «quality guarantees» of gene transfer turned out to be wrong.2.
Yes, in Sweden of the century before last, as in modern England, children from small families, as a rule, received the best education. Yes, for the most part they earned more. But at the same time, the number of heirs — the main criterion for evolutionary expediency — still turned out to be greater among women with many children. Quality did not translate into quantity.
Status or diapers?
Another well-known anthropologist, Sarah Hrdy, offers her explanation of the demographic shift. In her opinion, high fertility in itself is an advantage for female animals, but with human evolution, everything is somewhat more complicated. A woman gains evolutionary advantages by gaining a higher social status — and, as a result, the opportunity to have children from more status men.
Until the XNUMXth century, women’s opportunities in this regard were extremely limited. However, today they are almost comparable to the capabilities of men. And the higher the income, level of education and social status are valued in society, the more efforts a woman makes to achieve precisely these goals, pushing the birth of children into the background and even the third plan.
In addition, wealthy families tend to inherit not only genes, but also their wealth and social status. And to provide, for example, education in an elite private school is much easier for 1-2 children than 4-5. Therefore, in order to maintain their modern evolutionary advantages (wealth and status), wealthy people have fewer children.
Does it follow from this that in the future developed countries will be populated entirely by the descendants of families, to put it mildly, not prosperous?
Probably not. The same David Lawson showed, using the example of England, that the trend towards a decrease in the number of children is characteristic of both rich and poor families. Of the 7,7 million families he studied in 2012, only one in seven had more than two children. And the difference in prosperity did not play a decisive role.
In addition, it would be wrong to reduce the solution of the issue only to socio-cultural and economic reasons. For example, sociologist Anna Rotkerch showed that the desire to have children is largely determined by the personal characteristics of parents.3. For example, male extroverts become fathers more often than introverts. And for example, people who are prone to adventure and getting new experiences, on the contrary, have fewer children, apparently because they always find some more interesting and exciting activities.
Finally, we must not forget about the genetic predisposition
Numerous observations of identical twins confirm that these people (who have the same set of genes) tend to have the same number of children — regardless of the cultural or socio-economic conditions in which they live. And the point is not only in the physiological ability to conceive and bear a child, but also in motivation: the pattern persists even among twin women who have access to contraceptives.
In a word, it has not yet been possible to find out exactly why the rich have fewer children, although this is disadvantageous from the point of view of evolution. Perhaps this is the result of the preservation of the former psychological model of behavior, which is no longer valid in the conditions of a post-industrial society. But if we assume that those who are more likely to give birth to children are those who are inclined to this by virtue of their character, and even have the appropriate genes, then it is easy to understand that over time our planet will be populated entirely by the descendants of these people. Which — thanks to genes and upbringing — will quickly nullify the demographic shift, and there will simply be nothing to unravel.
1. D. Lawson, R. Mace «Sibling configuration and childhood growth in contemporary British families». International Journal of Epidemiology, 2008, № 37 (6).
2. D. Lawson et al. «Low fertility increases descendant socioeconomic position but reduces long-term fitness in a modern post-industrial society». Proceedings Biological sciences / The Royal Society, 2012, № 279 (1746).
3. A. Rotkirch et al. «Personality is differentially associated with planned and non-planned pregnancies». Journal of Research in Personality, 2013, vol. 47, № 4.