However, men can have more offspring with multiple sexual partners and thus are not as eager to settle down, said Kruger, who studies human behavior and motivation from an evolutionary perspective.
But the economics of supply and demand adds a twist, Kruger said.
"When women are scarce they have more bargaining power and can ask for more," Kruger said. "So the guys who are qualified will snap up the women and get hitched, whereas others need more time to build up their resources and social status."
As a result, the marrying age for men varies more widely when women are scarce, because younger men often have to wait until they're older to gather the resources to successfully compete for a mate, Kruger said.
"All things being equal, the guy with the better resources is going to win out," Kruger said.
The age gap between spouses also widens. The norm is for men to marry women three to four years younger but when women are scarce women can be five or six years younger on average, Kruger said.
For example in Las Vegas, where there are six men for every five women, the median marrying age for men and women is 28.3 and 24.5, respectively. Contrast that with Birmingham, Ala., where there are 11 women for every 10 men, and the median marrying age for men and women is 26.9 and 26.7, respectively.
When the ratio of men to women is greatly out of balance, it creates social tension and encourages markets for services like sex trafficking and prostitution, Kruger said. When there is a surplus of men, there are likely higher rates of accidents and violence as men engage in riskier behavior to compete for women and resources. When there is a surplus of women, sexually transmitted disease can increase as women become more promiscuous.
According to one study, by the year 2020 there will be 24 million more men than women in China, and if these men do not get married by age 40 they proba
|Contact: Laura Bailey|
University of Michigan