A possible cause of that fluctuating asymmetry is exposure to oxidative stress in the womb which interferes with proper development. The embryo requires energy to develop properly. As cells use oxygen to make energy, they can create free radicals. These are unstable molecules that can have chemical reactions with other molecules, causing the cell damage known as oxidative stress. Free radicals can be kept in check by antioxidants, but if there is an overabundance of radicals, the resulting oxidative stress can damage DNA and tissue. Oxidative stress is thought to be a major cause of mutations and to play a part in ageing and a host of diseases, including cancer…

Ten bilateral features of the men – ear width, ear height, wrist width, elbow width, lengths of four fingers, ankle breadth and foot breadth – were measured and compared. The men’s urine was measured for markers of oxidative stress and for hormones, and they were quizzed about any birth complications, such as late or premature birth, which can increase levels of oxidative stress. Finally, a group of women were asked to rate images of the men’s bodies and faces for physical attractiveness.

Results show that men who were rated as attractive by the women had significantly lower levels of oxidative stress. And men with more symmetrical bodies had lower levels and were rated as more attractive. Men who had experienced birth problems had higher levels of oxidative-stress markers.