【社会進化】永遠の大親友は本当に「永遠」なのか

An analysis of a large database of mobile phone usage, published in the journal Scientific Reports, highlights the differences between the differences between the friendship preferences of men and women and how these choices change throughout our lifetime. The patterns observed may reflect the way the reproductive investment strategies of the two sexes change across lifespan.

Robin Dunbar and colleagues analyzed a database of 1.95 billion phone calls and 489 million text messages to study gender preferences in close friendships and how these preferences change throughout lifetime. They focused on each individual’s three most preferred friends, as indexed by the frequency of contact, which has previously been shown to be a good proxy for emotional closeness.

The authors found that young people tend to prefer their ‘best friend’ (the person with whom they are most frequently in contact) to be of the opposite gender and same age group — probably their spouse. From the age of about 50, a woman’s male best friend tends to move into second place, replaced by a younger female, potentially her daughter. Conversely, men are more likely to have a female best friend throughout their lives. The results indicate that women may be more focused on opposite-sex relationships during their reproductively active years, suggesting they invest more heavily in creating and maintaining pair bonds. As they age, women’s attention shifts from their spouse to younger females, assumed to be daughters, reflecting, perhaps, a shift in reproductive strategy from mate choice to personal reproduction to grandparental investment.