A woman’s intense interest in her partner shifts when grandchildren arrive

The research by the University of Oxford in the UK, Finland, the United States and Hungary is published in the journal Scientific Reports.

With information limited to the gender and age of users from a large mobile phone database of three million subscribers, the researchers analysed the number and frequency of contacts each subscriber made over a seven-month period. Researchers defined a 'best friend' as the individual who the subscriber texted or called the most. Out of a total of two billion phone calls and half a million text messages, the researchers were able to rank each of the mobile phone user's 'best friends' in first, second and third place.

Researchers found that women spend more time and effort than men in maintaining a close relationship with a member of the opposite sex (boyfriend or spouse) from their early 20s. They found that a man's closest contact was his wife or girlfriend, but that level of contact was much steadier and less intense than for women.

The researchers suggest that from their early 20s, women are investing more of their time than men in finding a potential mate; but this intense interest tails off from the age of 45. The peak contact time with their daughters was likely to be when the woman was around the age of 60, the study found. At the later stage in life, women tended to be more likely to be in close contact with their daughters than their husbands or their sons. The research suggests that once fathers were around 50 years old they had peak contact time with their daughters, but at this stage fathers still spent about half as much time as the mothers staying in touch with their daughters.

Men communicated mostly with their wives, and there was what the researchers call a 'striking tendency' for men to have a greater gender balance in their close relationships. The researchers found that men did not discriminate at all on the basis of gender where their own children were concerned.

By contrast, women were found to be far more gender-biased in who they maintained close contact with at any given time. Co-author Professor Robin Dunbar, from the Institute of Cognitive and Evolutionary Anthropology at the University of Oxford, said: 'This suggests that the intimate structure of human social networks are driven much more by women's interests than by men's -- men are more casual in their social relationships, whereas women know what their social goals are and go for them.

'The researchers say that for the first time they have captured strikingly different patterns of behaviour between men and women which reflect how social strategies change in the course of our lives as a consequence of changing reproductive interests. Women were found to shift their relationship preferences, investing far more time and effort than men in communicating with the opposite sex when they were of childbearing age. Although this was previously suspected, the study remarks that until now this has been particularly difficult to test. Meanwhile, the study suggests that men are less strategic in their communications with their nearest and dearest. It notes that while scholars have tended to focus on male bonding behaviour in defining human sociality, this study underlines the importance of mother-daughter relationships in understand how the structure of human society has evolved.