Women tend to form deep and lasting friendships while men are more likely to make fickle friends over a pint or game of squash, says research published yesterday.
Members of the fairer sex make "deeper and more moral" friends and then stick with them through thick and thin.
By contrast, sociologists from the University of Manchester found that men tend to be more calculating about who they befriend, and are likely to base these relationships on social drinking.
The four-year study tracked the lives of 11,000 men and women between 1992 and 2002. Each of those taking part in the British Household Panel Surveys regularly filled in questionnaires about the state of their friendships.
Dr Gindo Tampubolon, from the university's School of Social Sciences, said his team had wanted to learn whether the nature of friendship had changed in recent years as technology had advanced.
One of his conclusions is that, in general, it has not. Indeed, in some situations mobile phones and computers had actually enhanced friendships.
"In years gone by people might have written a friend a letter, then waited for a reply. Now they can call them, visit them, email them, talk to them on MSN and swap photographs over the internet," he said.
Dr Tampubolen's research suggests that people are much more likely to socialise with those of their own gender - 75 per cent of best friends in the survey were of the same sex.
He said he had no idea how many of the best friends in the survey, whether same sex or opposite sex, went on to form romantic attachments or get married.
But he went on: "Friendship between women seems to be fundamentally different to friendship between men. It is much deeper and more moral. It is about the relationship itself rather than what they can get out of it.
"Women tend to keep their friends through thick and thin across geography and social mobility, and their view of friendship has something to do with how they express themselves and form their identity.
"Men, on the other hand, are more fickle with their relationships and seem more interested in 'What's in it for me?' "
On average, 36 per cent of the men in the survey contact their closest friend on a daily basis, compared with 47 per cent of women.
In the case of their second-best friend, the percentages dropped to 28 and 33 respectively. By the time third-best friends were considered the daily contact had reduced to 24 and 28 per cent respectively.
The disparity between sexes is partly explained by factors such as roles, occupations, class and leisure. However, there tended to be a fundamental difference between the sexes from an early age.
Girls in general had more "affirmative" friendships, while boys based their friendships on the activities they might pursue.
Career structures among men tended to result in them leading more transient lives than women.
Dr Tampubolon said the research reflected his team's view that friendship was not always a choice.
"We have contact with friends, family, neighbourhood and work which we are or are not able to turn into friendships," he said.
