Women, being from Venus, have a reputation for being the first to spring "I love you" in romantic relationships.
But men actually are more likely to utter those three loaded little words first, and men admit thinking about confessing love six weeks earlier than their female partners, according to an article to be published in the June issue of the Journal of Personality and Social Psychology.
That doesn't mean men are bigger saps. Taking an "evolutionary-economics" perspective, the article concludes that gender differences in the timing and function of saying "I love you" are related to whether a couple has had sex.
"Men may be more impulsive in the way they express love, but what love means to men and what love means to women may be very different," said co-author Josh Ackerman, assistant professor of marketing at MIT Sloan School of Management.
In a series of surveys, researchers found that two-thirds of couples report that the man was first in confessing love. Men also reported being significantly happier than women to hear "I love you" one month into the relationship if they had not yet had sex, while women felt happier than men when they heard "I love you" after the onset of sex in the relationship.
The researchers theorized that a pre-sex love confession may signal interest in advancing the relationship to include sexual activity - which is what men want, evolutionarily speaking, so as not to lose an opportunity to spread their genes. They want to "buy low," as the article put it. Women, who have more to lose if they get pregnant, prefer a post-sex confession as a signal of long-term commitment. They prefer to "sell high."
Furthering the point, the men happiest to get a pre-sex love confession were those interested in a short-term fling, while both men and women seeking a long-term relationship were happier hearing "I love you" post-sex.
Despite birth control and egalitarian values in modern society, these primitive patterns persist in the subconscious, Ackerman said.
The researchers hope exposing the biological underpinnings of these behaviors can help people understand the hidden meanings and motivations behind professions of love, which are ripe for misinterpretation.
Explore further: Talk is cheap: New study finds words speak louder than actions