An analysis of 1.95 billion cell phone calls and 489 million text messages reveal how men and women follow different relationship patterns during their lifetimes. The researchers argue that women's friendships in particular drive the process of finding a mate and supporting the next generation.
The data could also undermine traditional notions about how humans like to organize themselves. "There has been a view in anthropology that the ancestral state for humans is a form of patriarchy, and I'm not sure that that's true," says University of Oxford anthropologist Robin Dunbar, an author of the study published April 19 by Nature Scientific Reports. (Scientific American is a part of Nature Publishing Group.)
Dunbar and an interdisciplinary team examined cell phone data from a single provider in an undisclosed European country. (Specific locations were kept anonymous to protect cell phone users' identities.) The researchers worked with data gathered over a seven-month timeframe and restricted themselves to studying communications between cell phone users of a known age and sex, making a data set of about 3.2 million subscribers, or about 20 percent of the nation's cell phone users. Working on the assumption that close friends communicate most frequently, the team analyzed the top three friendships of each cell phone user based on the frequency of communication to spot patterns in the average male or female user at various ages.
The researchers expected to find "homophily," or the tendency for an individual to pick a friend like him or herself. Instead, it seems that romance trumps other forms of friendship: The data revealed that an individual's best friend, particularly in one's 20s and 30s, happens to be someone of the opposite sex and a similar age. In addition, striking differences exist in how men and women communicate with their presumed romantic partner. For one, the man in a woman's life was her very best friend for roughly 15 years, compared with seven years in the case for men. The peak age for partner parlance also differed: 27 years old for women and 32 for men.
After age 50, however, things change. The preference for a romantic partner peters out in both men and women, and toward the oldest age range in the data set, both sexes seek companionship first and foremost. For a woman, friendship with her man was replaced by a strong relationship with another woman, usually about a generation younger. Dunbar and his colleagues interpret this pattern as a mother–daughter relationship.
Putting together the strong preference in women for first a man and then a daughterlike figure, the researchers conclude that biology shapes female behavior, which in turn affects men. Dunbar suggests that women initiate and prioritize the relationship with a romantic partner earlier in life than men, an action that gradually leads men to reciprocate. This relationship remains top priority throughout the average woman's childbearing years. After that, she turns her attention to supporting the next generation of women as they approach childbearing.
"Generally, we have probably underestimated how important these family support networks are," Dunbar says. He speculates that contemporary declines in family size may reflect the mobility of modern women, isolating them from their supportive maternal network. In addition, he believes that the bonds between mother and daughter and the strength of a woman's influence on mating are so strong that they may underlie human society's natural tendencies. "I think the default for humans, if all else is equal, is actually a matrilineal society."