Maria da Graca Bicalho and her colleagues at the University of Parana in Brazil reported that this was likely to be an evolutionary strategy to ensure healthy reproduction because genetic variability is an advantage for offspring.

Bicalho said: ‘Although it may be tempting to think that humans choose their partners because of their similarities, our research has shown clearly that it is differences that make for successful reproduction, and that the subconscious drive to have healthy children is important when choosing a mate.’