A new global research has shown that people have more sex in countries with higher gender equality.
The study is part of a big-picture look at sexual behaviors worldwide using "sexual economics".
"Women's sexuality has a kind of value that men's sexuality does not," The Globe and Mail quoted study author Roy Baumeister, a psychologist at Florida State University in Tallahassee, as telling USA Today.
"Men will basically exchange other resources with women to have sex, but the reverse doesn't work," he added.
Baumeister and his colleagues used data from 37 countries, including an international sex survey of 317,00 people.
They found that countries ranked higher in gender equality also generally had more casual sex, more sex partners per capita, younger ages for first sex and greater tolerance/approval of premarital sex.
But the opposite was true in countries where women were at a disadvantage.
When women lack opportunities, they restrain sex to drive up the price, prompting men to commit to a lifetime of support -- a.k.a. marriage -- to get sex.
"It''s a notoriously unromantic theory," he acknowledges.
Other researchers insist it has legs.
Sex is a matter of supply and demand, said Mark Regnerus, a sociologist at the University of Texas-Austin and author of Premarital Sex in America.
"On average, men want sex more than women do," Dr. Regnerus writes at Slate.com.
The study is published in The Journal of Social Psychology.