Another argument against
delaying first-time childbirth

Delaying first-time childbirth into the 30s or later may make it less likely an older mother’s lineage will survive over time, according to a University of Michigan researcher.
“We older moms are going extinct,” said Bobbi Low, a behavioral ecologist at the university’s Institute for Social Research, who gave birth to her first and only child when she was in her mid-30s.
Low and her collaborators used statistical models to determine how much the advantages of better education and higher income that older moms enjoy compensate for delayed first births and lower lifetime fertility projected out a few hundred years.
After running the model over 220 years — about as long as the United States has been an independent nation — the researchers found that wealthy, late-reproducing women declined as a proportion of the population, from 11 percent to about 5 percent. The proportion of the poorest women also declined.
But the proportion of lower-middle-class women increased dramatically, from about 33 percent to 60 percent. “Under almost all conditions in the models, we found that reproduction in the early 20s led to the greatest lineage success for women,” Low said.
“In any species, other things being equal, whoever keeps their family line going and growing persists, while others go extinct,” said Low, author of the book “Why Sex Matters” and a professor in the School of Natural Resources and Environment. “In many cases, including that of humans in the past, keeping the line going has been 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 ’superkids’ do well,” Low said. And so some women have started to shift from simply offering reproductive potential 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.”
The analysis by Low and collaborators Carl Simon and Kermyt Anderson suggests that women who traded off having children earlier to amass more resources may have lost the longer-term game of evolutionary survival.