The research, led by Robin Dunbar, head of the Institute of Cognitive and Evolutionary Anthropology at Oxford University, showed that men and women were equally likely to lose their closest friends when they started a new relationship.

Previous research by Dunbar’s group has shown that people typically have five very close relationships – that is, people whom they would turn to if they were in emotional or financial trouble.

“If you go into a romantic relationship, it costs you two friends. Those who have romantic relationships, instead of having the typical five ‘core set’ of relationships only have four. And of those, one is the new person who’s come into their life,” said Dunbar.