Sept. 30, 2008— -- Money can't buy love, but it seems to earn you more babies. Rich men sire more children than paupers, according to a new study of thousands of middle-aged British men.
Women are more likely to marry men who can provide for them and their children than penniless men, says Daniel Nettle, a behavioural scientist at Newcastle University, UK, who led the new study.
"It's not that if you're richer you'll have more children – if you're richer you're less likely to be childless," he says.
For much of civilization, females have tended to mate with better providers, but many sociologists argue that the industrial and sexual revolutions have immunised people in developed countries such evolutionary pressures.
Census surveys have suggested that wealthier men have fewer kids, says Rosemary Hopcroft, a sociologist at the University of North Carolina in Charlotte, who is not affiliated with the study.
No more kidsHowever, these surveys are problematic because they tend to look at household income and tally only a mother's children, she says. The children of divorced and remarried men tend to get left out.
To correct for this bias, Nettle and Newcastle colleague Thomas Pollet looked at previously gathered data on more than 11,000 British men and women, all born between 3 and 9 March 1958, called the National Child Development Study.
The study has tracked income, marriage and fertility of study participants since birth. "It's a great resource," Nettle says.
Now that study participants have entered their late 40s – the study used data from 2004 – nearly all participants have stopped having children.
With carefully collected figures on male and female income and fertility, Nettle and Pollet found that, for men, the more money they make, the more kids they sire on average. Men who earn £10,000 a year fathered one child on average, while fathers who pulled in £50,000-plus sired more than two kids.
But rich men didn't have larger families, rather they are more likely to find mates, Nettle says.
So despite the industrial revolution, gender equity, and birth control, rich and powerful men are more likely to pass on their genes than poorer and less powerful men.
"A deep aspect of the way human society works is that men with a lot of resources use their resources to achieve high reproductive success," says Nettle. "In a way, what we're saying in this paper is that a modern industrial society like Britain isn't so different."
The difference between modern Britain and medieval Europe or contemporary African hunter-gatherers is a matter of degree, not kind, he argues.
Human selection for male wealth even compares with sexual selection in animals for male traits favoured by females, Nettle and Pollet found. Based on a quantitative database of animal traits known to affect female choice, male wealth fell square in the middle.
The power of sexual selection for wealth in males compares to bill size in the large cactus finch, one of Darwin's Galapagos finches, Nettle says.
But while a peacock's tail or a bull's horns have an obvious basis in biology, male wealth is harder to pin to genetics, Nettle says. Ambition, intelligence and financial savvy probably have some heritable aspects, but social status, inheritance and upbringing are just as likely to affect a son's future income, he says. "We get so much from our parents, as humans, besides genetics."