When surveyed, most people say they get tattoos or unconventional piercings to express individuality. But could something more psychologically primal be afoot? Researchers at the University of Wroclaw in Poland measured about 200 men and women—half of them inked or pierced in places other than their earlobes—for body symmetry, or how similar their right and left sides are. (More similarity indicates genetic health and is associated with sexual attractiveness.)

Among the research subjects, men with bodily decorations exhibited greater symmetry than those without, whereas no differences emerged in women. Because people who are less symmetric did not opt more often for tattoos and piercings, researchers rejected one widely held hypothesis that suggested people use physical graffiti to hide or distract from imperfections in their appearance.

The results jibe with a different theory—getting stuck with needles can endanger one’s health via infections, so the study supports the evolutionary “handicap” theory that only those with high biological quality can afford such risky behavior. The im­pulse to get inked may be a risk-taking behavior inherited from ancestors who were strong enough to endure injuries and survive—as opposed to those whose ancestors survived by avoiding risk and injury. Therefore, at least in men, body art could serve as an “honest” signal of fitness in the Darwinian sense. So maybe that’s why pierced, tattooed rock stars do so well with the ladies.