Is that guy sexy? Is that woman beautiful? If you ask these questions to a group of people, they may have different answers, and a new study hints at why: Your perception of other people's attractiveness is mainly the result of your own experiences.
In the study of twins, researchers found that a person's environment plays a bigger role than genes in shaping whom they find attractive.
The idea that beauty is in the eye of the beholder has been around for a long time, said Laura Germine, a psychiatric researcher at Massachusetts General Hospital in Boston and lead author of the new study. But the scientific study of this idea has been limited, she said. [Seeing Double: 8 Fascinating Facts About Twins]
Most research on perceptions of attractiveness has focused on finding which characteristics people generally find attractive in others' faces, Germine told Live Science. For example, researchers have found that faces that are more symmetrical are generally more attractive, she said.
In the new study, published Oct. 1 in the journal Current Biology, the researchers looked at 547 sets of identical twins (who have identical DNA) and 214 sets of fraternal twins (who share half their DNA) in the Australian Twin Registry. The participants looked at 98 male faces and 102 female faces, and gave them a rating based on how attractive they thought the faces were. The researchers then used these ratings to come up with what they called "individual preference scores", which were a measure of how much each participant's ratings differed from the ratings of the average of all people in the study, according to the study.
In the first part of the study, the researchers found that if they selected two participants at random, the participants agreed on the attractiveness of a face 48 percent of the time on average, and disagreed 52 percent of the time.
That's consistent with a previous study that found that, on the one hand, fashion models can "make a fortune with their good looks" but friends can still "endlessly debate about who is attractive and who is not," the researchers wrote in the study, quoting an earlier study of the topic.
Next, the researchers set out to determine whether genes or the environment was a bigger influence on how people perceived attractiveness. In other words, they wanted to figure out what accounted for the 52 percent disagreement rate they saw in the first part of the study.
For each twin pair, the researchers compared the preferences of one twin to those of the other, to determine how similar they were. Then, they compared the similarity of all of the identical twins' preferences to those of the fraternal twins, Germine said.
If the identical twin pairs had preferences that were more similar than those of the fraternal twin pairs, it would suggest that genes play a bigger role, Germine said. But if the identical twins' preferences were not more similar to each other, it would suggest the environment plays a larger role, she said.
The researchers used standard calculations, that are often used in twin studies, to figure out the relative influence of the participants' genetics and their environments on their ratings of people's attractiveness. They concluded that people's individual environments accounted for most (78 percent) of the differences in how people perceived attractiveness.
And even for each twin in a pair, a person's individual environment is unique, the researchers said.
For example, even though twins share a lot of their environment because they usually grow up together in the same house, their individual environments -- including their friends, what they see in the media and their first relationship -- differ enough to give each twin an individual perception of attractiveness, Germine said. Previous research has shown that if people see a face and associate it with something positive, they tend to find that face more attractive, she added.
The researchers noted that shared environments (as opposed to individual environments) may still play a role in influencing people's preferences, but for this study, the population included was not very diverse.
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