People in rich countries have fewer children and more countries are getting rich. This means that, most likely, world population will stabilize and may even decline. The Malthusian doomsday is unlikely to arrive. One result of this decline in childbirth may be longer average lifespans, because children are bad for your health:
A pair of researchers, drawing on the experience of nearly 22,000 couples in the 19th century — has measured the “fitness cost” of human reproduction. This is the price that parents pay in their own health and longevity for the privilege of having their genes live on in future generations. The findings, published last month in the Proceedings of the National Academy of Sciences, manage to be both predictable and surprising.
Not surprisingly, women paid a bigger price than men. Older mothers were four times as likely to die in the year after having a child than their mates. Having lots of children was especially risky. A mother of 12 had five times the risk of dying prematurely as a mother of three.
So far, so unsurprising: childbirth is dangerous. But here’s the kicker:
Even after their child-bearing years came to an end, women who had had many children died earlier than women who had had few.
A possible explanation is that stress kills:
As cells age, chromosomes, where genetic information is stored, lose material from their ends, the DNA-protein structures called “telomeres.” When telomeres get too short, a cell can’t divide any more. It becomes senescent, or terminally old.
A study published in 2004 by Elissa S. Epel of the University of California at San Francisco measured telomere length in 39 mothers who were caring for children with chronic illnesses and 19 mothers raising healthy ones. She found that among the mothers of the sick children, the longer a woman had cared for her child, the shorter her telomeres. This was true even after adjusting for the telomere shortening that comes purely with age.
Between the women with the highest and lowest scores on a test of psychological stress, telomere lengths differed as much as between people 10 years apart in age.
So you can get your genes into the next generation, but at a price: less life. Of course, this raises the question of how much life does one really need. The marginal benefit of an extra year of life at, say, 80 is not that great, as far as I can see from watching folks age. (Then again, check back with my when I’m 80: I’ll probably have a different opinion—“Just one more bingo game! Please, Mr. Grim Reaper! Not yet!”) Also, we may soon be able to correct for this sort of cellular damage.