- Women attempting to have children will find having a circle of close friendships helpful.
- Having five close friends may boost a woman’s fertility.
- Those lacking group of close confidantes are more likely to see their monthly cycle disrupted.
- Women can maintain friendships with just telephone conversations.
Women can maintain their friendships by chatting with each other regularly by telephone. By contrast men need to meet up, such as going to the pub or playing football to maintain friendships.
Oxford researchers found a gender divide when it comes to friendships. Professor Dunbar followed a group of 30 teenagers as they left home to start university or move home to pursue their careers. He looked at why some friendships lasted, while others drifted apart.
Professor Dunbar said, "What determined whether they survived with girls was whether they made the effort to talk more to each other on the phone. The telephone was only of any use to the girls though. Talking had absolutely no effect on boys' relationships at all."
Professor Robin Dunbar of Oxford University said that those lacking group of close confidantes are more likely to see their monthly cycle disrupted.
And Professor Dunbar claimed the stress of maintaining too many casual acquaintances - rather than a core of five close friends - will also have a disruptive effect on a woman's hormones.
He said, "The size of relationships place huge stress on endocrinology [hormone levels]. It can destabilise the menstrual cycle and cause infertility. Having too many casual acquaintances makes you infertile. You see it in primates."
Professor Dunbar, bases his theory on research in primates that found that female monkeys lacking a close 'coalition' of allies are more likely to be infertile.
'What held up their friendships was doing stuff together. Going to a football match, going to the pub for a drink, playing five a side. It was a very striking sex difference.
'The caricature is if you move away to another town, girls will be on the phone or Facebook with each other to keep the relationship going. 'With guys, it is 'Out of sight out of mind'. They just find four more guys to go drinking with.'