What makes a face sexy? Many cultures prize high foreheads, strong cheekbones, and facial symmetry, but a new study suggests that no single male or female chin shape is considered so universally beautiful that it influences partner choice.

Dartmouth College researchers wanted to explore the universal facial attractiveness (UFA) hypothesis, which suggests that certain facial features are selected as markers of mate quality for people of the opposite sex across all cultures. The UFA hypothesis is based on cross-cultural studies of perceived attractiveness, many of which drew conclusions from showing study participants a series of male or female faces and asking which they preferred.

Certain features, like bilateral symmetry, seemed to be universally preferred even without exposure to Western standards of beauty, but the Dartmouth researchers suspected that preference is only one part of the story. If certain facial features are universally attractive, and attractiveness is an indicator of reproductive success, then sexual selection would lead those features to be widely expressed at similar rates across cultures.

Dartmouth researchers Seth Dobson and Zaneta Thayer decided to test the concept of sexual selection for traits of universal beauty by focusing on variations in chin shape, which is often considered an indicator of facial attractiveness across cultures. Men with broad chins are generally regarded as more dominant and masculine, while women with small or narrow chins appear more feminine.

They observed the variation in chin shapes among 180 healthy male and female skeletons from nine areas in Australia, Africa, Asia, and Europe. The skeletons' jawbones were scanned and digitized, then statistically analyzed.

Their results, published in the journal PLOS ONE last week, contradict the idea of sexual selection for markers of universal human beauty, at least in regard to chin shape. While male chin shapes were consistently broader than those of females across cultures, there were significant geographic differences among individual chin shapes in both sexes.

"If people from all over the world exhibit similar chin shape preferences, as the UFA hypothesis suggests, and if mating preferences influence morphological evolution, as implied by sexual selection theory, then we would expect to see negligible geographic variation in chin shape," wrote the researchers. "Our results suggest that this is not the case."

Dobson and Thayer don't rule out the possibility that certain facial features are universally preferred, or that sexual selection is still occurring, but concludes with the shocker that specific markers of physical attractiveness, like chin shape, can be overpowered by cultural factors and social bonds when it comes to mating.

That's a relief for the weak-chinned men and strong-jawed women among us who hope to pass on their genes.

The full study is available for free at PLOS ONE.