http://www.nytimes.com/2009/07/07/health/07dating.html?ref=science 

 

July 7, 2009

Testing Evolution’s Role in Finding a Mate

By SARAH ARNQUIST

Scientists have long observed that women tend to be pickier than men when choosing a mate. The usual explanation is evolutionary: because women have a bigger investment in reproduction — they are the ones who have to endure pregnancy, childbirth and breast-feeding — they need to hedge their bets against selecting a dud to be the father.

In recent years, the emergence of speed dating has given psychologists, economists and political scientists new ways to test this and other hypotheses about mating. Because participants can be randomly assigned to groups and have no prior information about other participants, three-minute speed-dating sessions are about as close to a controlled experiment as researchers are likely to get.

Now, two scientists at Northwestern University have published an experiment that challenges the evolutionary hypothesis. The study by Eli J. Finkel and Paul W. Eastwick was published last month in the journal Psychological Science.The experiment looked at speed-dating sessions to determine whether men or women were choosier. The answer, it turned out, was neither. Regardless of gender, people who were instructed to approach other daters were less selective — that is, they were more likely to ask to meet later for a date.

Dr. Finkel and Mr. Eastwick write that this does not mean men were just as selective as women. But the scientists suggest that the explanation for the gap lies in social conditioning rather than evolution.

By making the first move, a person gains confidence and then finds more people attractive, the theory goes. Culturally, men are expected to approach women more often, which may boost their confidence and make them less selective. Citing what social psychologists call the scarcity principle, Mr. Eastwick and Dr. Finkel write that “individuals tend to place less value on objects or opportunities that are plentiful than those that are rare.” By contrast, they say, women are accustomed to being approached, which may make them feel more desirable and thus more selective.

Scientists have also used speed-dating experiments to examine the tendency for people to mate with people like themselves. A 2006 paper by economists at the University of Essex in England analyzed data from 3,600 male and female speed daters to see if people selected mates with similar traits, like height and education, because that is what they prefer or because they are most likely to encounter them in the dating market.

The economists, Michèle Belot and Marco Francesconi, found that men’s preferences for occupation, height and smoking had little effect on whom they asked out. Those factors also did not matter to women, but age did.

In homogeneous environments, Dr. Belot and Dr. Francesconi wrote, people are more likely to marry others like themselves, while more diverse communities are likely to produce more varied pairings.

“Mating requires meeting,” they wrote. “The pool of potential partners shapes the type of people to whom subjects propose and ultimately with whom they form long-term relationships.”

People narrow their market opportunities, the economists suggested, by selecting for height, weight and age, which tend to be proxies for socioeconomic status.

So how does a person increase the odds of crossing paths with someone who matches his or her preferences? Maybe by tapping into social networks. In “Connected: The Surprising Power of Our Social Networks and How They Shape Our Lives,” a book to be published in September, Dr. Nicholas A. Christakis of Harvard Medical School and James H. Fowler, a political scientist at the University of California, San Diego, argue that dating is not a random process.

They cite a landmark 1992 Chicago sex survey of 3,432 adults ages 18 to 59, which found that 68 percent of married people in the survey reported meeting their spouse through a friend, family member or other mutual acquaintance.

“If you are single and you know 20 people reasonably well, and if each of them knows 20 other people, and each of them knows 20 other people,” Dr. Christakis and Dr. Fowler write, “then you are connected to 8,000 people who are three degrees away. And one of them is likely to be your future spouse.”