An average of 2.11 births per woman are needed to sustain a population. The birth rates of all European countries and Japan are well below this level. The U.S. birth rate is slightly below this level.
Here's a gloomy idea. No population in which there is substantial equality between men and women is maintaining its numbers at the present level of technology. Only the populations in which women are substantially oppressed are growing. As more and more equality of the sexes is achieved, the birth rate of a country declines.
In the U.S. the only white populations which are growing are the Mormons and the ultra-orthodox Jews. In both women are oppressed relative to the standards of the general population. Apparently the part of the black population in which men don't marry the women who bear their children and contribute to their support is increasing. Its increase depends on government support of single mothers.
The problem with the Mormons and ultra-orthodox Jews is that both of their religions are unsupported by science. Moreover, their oppressiveness, not only of women, generates many defections into the general population.
Equality advanced fastest among the more intelligent, and their birth rates declined the fastest. The result has probably been an absolute decline in the number of highly intelligent people. There are still enough to sustain science and technology.
What might happen to reverse this decline? There are several possibilities.
If there are any secular sufficiently inequalitarian populations, their size will increase provided they don't have too many defections. I don't know of any.
If there are any genes that motivate people to have more children, natural selection will select for people who have them. The problem would then solve itself. I don't believe any such genes have been identified as yet.
If there are cultural features of a subpopulation that lead to a higher birth rate, and this subpopulation maintains its identity and doesn't have too many defections, it will increase relative to the general population. Whether there are any such subpopulations in Europe or Japan has not, so far as I know, been investigated. The Jews were such a subpopulation but apparently are not any longer.
There could be very large subsidies for children, much larger than those at present. However, it's not just a matter of money. The rich don't have a sustainable birth rate either.
Here's a possible moralistic solution. Make it a matter of morality to have enough children and for men to do more to help take care of them. In general moralizing doesn't work, but if the anti-natal propaganda dies out, there may be a chance. The Jewish population of Israel had, the last time I asked, an adequate birth rate, but I don't know the extent to which this depended on the orthodox. The birth rate was still less than that of the Arab population of Israel.
Here's a possible technological solution. If the age range in which a woman can have children and have the energy to care for them could be sufficiently increased, e.g to 50 years, many women and their husbands might be motivated to have second families.
Here's an institutional solution. The government might subsidize women to have children and then take over their support.
This preliminary discussion has a substantial element of guesswork. I welcome corrections.
Up to: Sustainability of progress
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