Phone data shows romance 'driven by women'
That changes as their daughters become old enough to have children, after which they become the most important person in their lives.
The study has been published in the journal Scientific Reports .
It also shows that men call their spouse most often for the first seven years of their relationship. They then shift their focus to other friends, BBC reported.
The results come from an analysis of the texts of mobile phone calls of three million people.
According to the study's co-author, Professor Robin Dunbar of Oxford University, UK, the investigation shows that pair-bonding is much more important to women than men.
"It's the first really strong evidence that romantic relationships are driven by women," he told BBC News.
But the data shows that women start to switch the preference of their best friend from about the mid-30s, and by the age of 45 a woman of a generation younger becomes the "new best friend", according to Professor Dunbar.
"What seems to happen is that women push the 'old man' out to become their second best friend, and he gets called much less often and all her attention is focussed on her daughters just at the point at which you are likely to see grandchildren arriving," he says.
Prof Dunbar also claims that the findings suggest that human societies are moving away from a patriarchy back to a matriarchy.
The aim of the project was to find out how close, intimate relationships vary over a lifetime.
This kind of anthropological study is normally very difficult to do because it is hard for researchers to get such a big picture of people's lives.
But by looking at an at an extremely large mobile phone database, they were able to track these changes extremely accurately.
They had access to the age and sex of the callers, who between them made three billion calls and half a billion texts over a period of seven months.
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