To study infidelity, researchers scanned publicly accessible ads from 200 men and 200 women chosen at random from the site.
"The study of adultery is important in the broad sense, because it helps us understand who we are," Live Science quoted researcher James Hare, a behavioural ecologist at the University of Manitoba in Canada, as saying.
“Time and time again, data reveal that we are a product of the same selective forces and evolutionary processes that have shaped all life. To me, acceptance of this fact diminishes the sense of entitlement humans feel and, in the end, fosters an ethic that is more in accord with the world around us,” he said.
The researchers investigated what the would-be cheaters said they wanted in an adulterous relationship: "anything goes," "short term," "undecided," "long term," "cyber affair/erotic chat," or "whatever excites me."
They also noted the total number of adjectives they used in describing themselves and in what they wanted in a partner.
Their findings conformed to common stereotypes of men as promiscuous and women as choosy – while for men ‘anything goes’, women sought long-term relationships about two-thirds more than men.
In addition, women used more adjectives to describe the wealth and physical attributes they wanted in partners, while men used more adjectives when it came to describing their own wealth, athletic interests and educational achievements.
Women in relationships are driven more by urges for good genes for potential progeny than for material benefits, Hare said.
Although the women in this study were near or past the end of childbearing age, "many of the women would still be capable of reproduction," he added.
Even for those who were not, there is still "the satisfaction derived from mating with a physically fit partner," Hare said.
The findings are published online Oct. 17 in the journal Evolutionary Psychology.