With so much concern about the difficulty of adjusting the biological clock to bear a child later in life, the future of descendants may not seem important to many people. But for those interested in their family's end-game evolutionary success as well as near-term parenthood, reproducing late in life is apparently a no-win strategy.
"We older moms are going extinct," says Bobbi Low, a behavioral ecologist who has just been appointed to direct the Evolution and Human Adaptation Program at the U-M Institute for Social Research (ISR). With U-M collaborators Carl Simon and Kermyt Anderson, Low has been using statistical models to determine how much advantages in education and income compensate for delayed first births and lower lifetime fertility a few hundred years down the road. The analyses appear in a recent article in the American Journal of Human Biology and a chapter in the forthcoming book, "The Biodemography of Fertility."
"In any species, other things being equal, whoever keeps their family line going and growing, persists while others go extinct," explains Low, the author of "Why Sex Matters" and a professor at the U-M School of Natural Resources and Environment. "In many cases, including that of humans in the past, that is best accomplished by making the most babies. But in modern societies, the number of kids is no longer the name of the game. The environment is so competitive that only 'super kids' do well. So women, quite reasonably, have started to shift from offering just reproductive value in the 'mate market' to offering a combination of reproductive and resource value---not just youth and good looks, but a good education and a good job."