Neuroscientist Dahlia Zaidel of UCLA said that tying asymmetries to fitness, as this new study does, is to generalize an idea.
"In humans, there are too many natural asymmetries to assume ideal fitness," she said. "Perhaps, though, fitness in humans means normal presence of natural asymmetries."
Zaidel set out to try and resolve the question of facial symmetry's role in attractiveness several years ago, when she digitally cut faces in half and copied and reversed the image to create faces that were perfectly symmetrical.
"When I looked at such perfection, I found that viewers consider such faces to be unattractive," she said. "They were found significantly less beautiful than the original faces that gave rise to them."
Zaidel explained that these results are ingrained in us from birth.
"Even babies originally smile asymmetrically," she said. "From birth, we are used to looking at faces and bodies that are not symmetrical."
In the case of the study, Zaidel said that differences that make someone significantly less fit fall into the realm of deformities.
More research is needed to determine precisely what constitutes a deformity, she said, and "people don't know the answer, but I imagine that there is a continuum."
Zaidel noted that a number of bodily features are asymmetric on almost everyone, including feet, where one shoe invariably fits better than the other, and women's breasts.
She said that women are slightly more asymmetrical than men, which often leads them to move their heads more when they speak.
Men do this less, she said, "and, of course, it drives women crazy," because they may think that the men are not engaged with what they are saying.
Ultimately, Zaidel said, trying to find perfect symmetry in people is futile in the first place.
"Nobody is perfectly, perfectly symmetrical," she said. "Even the most beautiful women, the most handsome men, don't have perfectly symmetrical faces or bodies."