Scientists have tried to explain how perceptions of a person's sexual orientation are influenced by their facial symmetry and proportions.
According to researchers at Albright College in Reading, Pa, self-identified heterosexuals had facial features that were slightly more symmetrical than homosexuals. And the more likely raters perceived someone as heterosexual, the more symmetrical that person's features were.
"The ability to assess the sexual orientation of others may be an adaptive trait," Newswise quoted Susan Hughes, lead suthor of the study as saying.
"In terms of mate selection and romance, it's crucial to recognize others' sexual orientation," she said.
The study showed the photographs of 60 men and women, 15 straight men, 15 straight women, 15 gay men and 15 lesbians, to a group of 40 participants (15 men, 25 women) who assessed the sexual orientation of those seen in the photographs.
The raters indicated the gender to which the person in the picture was most sexually attracted using a five-point continuum scale (1-only men, 2-mostly men, some women, 3-men and women equally, 4-mostly women, some men, 5-only women).
"We found differences in measures of facial symmetry between self-identified heterosexual and homosexual individuals," Hughes said.
"We also found that the more likely raters perceived males as being attracted to women (i.e. holding more of a heterosexual orientation), the more symmetrical the males' facial features were," she said.
Likewise, the researchers found that there was a tendency for straight women to be more symmetrical, although it was not statistically significant.
The study also examined sexual dimorphic facial measures - i.e. how masculine or feminine a face appeared - and found heterosexual men had overall more masculine features than did gay men.
This was also used by the raters in assessing orientation, the more masculine a man's face was, the more likely he was perceived as heterosexual.
"We were surprised to find that symmetry played a larger role than masculine or feminine features in assessing sexual orientation," Hughes said.
"But it appears that individuals use cues of symmetry to make assessments about one's sexual orientation and may be one of the features that comprise a person's 'gaydar' abilities," she added.
The study has been published in The Journal of Social, Evolutionary, and Cultural Psychology.