In a world of matinee idols and cover girls it's easy to assume that humans want their men to be manly and their women womanly.
But a groundbreaking new study suggests that, rather than being a preference passed down through a long process of social and sexual selection, it's a relatively new habit that has only emerged in modern, urbanised societies.
A team of psychologists, anthropologists and biologists, led by Brunel University London, surveyed 12 populations around the world, from the primitive to the highly developed.