Women speak to their male partners less often as they grow older and turn their attention to a younger generation, according to an unusual study Thursday that tracked nearly two billion phone calls and text messages.
The findings back evolutionary theory about the role of women in the survival of the genes, according to the probe by researchers in Britain, Finland, the United States and Hungary.
The investigators tracked the origin and destination of cellphone calls and text messages among 3.2 million people over seven months.
The changing web of contacts showed how men and women's social strategies mutate over time, the paper says.
"This suggests that the intimate structure of human social networks are driven much more by women's interests than by men's," said Robin Dunbar from Oxford University's Institute of Cognitive and Evolutionary Anthropology.
"Men are more casual in their social relationships, whereas women know what their social goals are and go for them."
Women spent more time communicating with the opposite sex when they were of childbearing age, the scientists said.
After the age of 45, women tended to shift their attentions to a much younger female -- presumed to be a daughter -- as their focus shifted to grandchildren.
Men's most frequent contact throughout their lives was consistently with their wife or girlfriend, although they made fewer calls than women did.
Co-author Kimmo Kaski of Finland's Aalto University told AFP the results were "maybe sort of obvious", but this was the first evidence borne out by actual data.
The researchers knew only the age and gender of the subjects, the duration of their calls and the number of messages sent, as well as their postal codes. The information was provided by an unidentified phone company in a European country. Identities and other data were withheld.
The study appears in the journal Scientific Reports.