Here's a thought provoking article about evolution and childlessness.
Now the author has an interesting point when he writes "For more than 99.99 percent 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 this is not the end of the the story. For many thousands of years, humans understood the link between sex and having children. Women seem to spend a lot of time thinking about babies. This is evidence enough for me that women have a genetically programmed desire to have children, and childbearing isn't just about a biologically programmed desire for sex.
So what then explains the childlessness of modern women? I think that there is another misplaced biological impulse; the need for humans to feel resource-secure before having children. In the past, there was probably an evolutionary benefit to delaying having children in times of resource scarcity. This resource scarcity was usually the result of something temporary like a drought. By waiting for the drought to end before starting a family, women increased their chances of raising a healthy child to adulthood.
We saw this biological impulse on a macro level after World War II. Women felt more secure after the war ended and they started having lots of babies. But this period of feeling secure didn't last too long.
The problem today is that most people in their childbearing years are resource-insecure. As I previously blogged, young people are comparatively worse off today than they were a generation ago.
This is a problem unique to the present day. In the past people reached their peak earnings capacity at an early age--when they reached physical maturity. An 18 year old is a much better farmer than a 40 year old because farming mostly involves physical labor. But in modern society the ages are reversed. An 18-year-old today qualifies for little better than a minimum wage job.
When people estimate their level of resource-security, they look to their own family as a baseline. So poor women, ironically, feel more resource-secure than rich women. Poor women can earn the exact same welfare check as their mothers did. But upper middle class people need many years of education and work experience before they can be as resource-secure as their parents. And because of regression towards the mean, children of the poor are likely to do better than their parents, but children of the well off are likely to do worse.
The problem of childlessness (if it really is a problem) will go away in a few generations. The genes that cause people to not have children when they feel resource-insecure are rapidly being culled from the gene pool.