Men are more prone to competitive risk taking and violent behavior, so what happens when the number of men is greater than the number of women in a population?
According to research by Florida State University Professor of Psychology Jon Maner, the answers might not be what you expect.
"When men outnumber women in a given ecology, intuition might suggest that rates of violent crime would skyrocket, marriages would destabilize and many children would be born out of wedlock," he said. "Intriguingly, the opposite has been observed."
Maner's study, "Ecological Sex Ratios and Human Mating," was published in the journal Trends in Cognitive Sciences. The study was based on a review and analysis of previous work on the topic conducted by Maner and others.
Although ecological sex ratios have been investigated extensively in nonhuman species, they play a crucial role in humans as well. Many factors can produce sex ratio imbalances, including wars, which kill more men than women, and sex-differentiated migration patterns.
"One of the central ideas is that when there is an imbalance in sex ratios, whichever sex is in the majority faces a lot more competition when it comes to finding and retaining romantic partners," he said. "One way in which that competition expresses itself is in the way both men and women shift their overall mating strategy toward the typical mating strategy of the other gender."
In order to compete, many male species will often resort to competitive risk taking or violent behaviors to attract females. In human males this means attention-grabbing, riskier behaviors like overextending financially to purchase status symbols, riding motorcycles and fighting.
But there are other male responses that are lesser known and, Maner pointed out, more typical of females.
"Another way men can compete with one another is by being quicker to settle down with one woman, get married and really devote himself more fully to having kids and being a good parent," he said. "On the other hand, if he isn't able to find a partner, he might be inclined to compete in other ways and that's where you might find increased violence, risk taking and competition with other men."
Maner said his study also revealed this crisscross of traits works in the opposite direction with women adopting behavior more typical of men when they are in the overrepresented population.
"When women are more abundant, they are more open to casual sexual relationships, less likely to get married," he said. "They are essentially catering to what is often the trait among men, which is to play the field."
For those in overrepresented populations who might already have trouble finding a mate, competition to win a mate's affections can get especially difficult. Maner mentioned men of low socioeconomic status as an example.
"They are generally less desirable to potential partners and their mating opportunities are limited," he said. "They face especially fierce competition, so they are especially inclined to find a partner and settle down quickly."
Associate Professor of Psychology Joshua Ackerman of the University of Michigan co-authored the study.