One of the earliest examples of behavioral asymmetry in humans is the tendency for the head to turn right in the last few weeks in the womb and the first six months after birth. This is thought to influence perceptual and motor preferences by increasing visual orientation to the right, but how this translates to subsequent adult behavior patterns has been unclear. In a Brief Communication in the February 13 Nature, Onar Güntürkün at the Fakultät für Psychologie, Rhur-Universität Bochum, Germany, shows that this distinct orientation bias persists, and is evident in even the most romantic moments (Nature, 421:711, February 13, 2003).

Güntürkün observed kissing couples at international airports, large railway stations, beaches and parks in the United States, Germany and Turkey. To ensure that extraneous factors were not influencing head-turning, he only counted the first kiss of couples who made lip contact, were in a face-to-face position, and who were not holding objects in their hands (which may induce a side preference). Of 124 couples, 80 (64.5%) turned right and 44 (35.5%) turned left, a roughly 2:1 ratio (P<0.05), suggesting that adults, in common with embryos and neonates, have a head-turning bias towards the right. The incidence of right-handedness is 8:1 and is therefore unlikely to have influenced head-turning behavior.

"By fostering a constant bias towards the right , this mechanism may be able to induce or enhance right-sided asymmetries of perception and action," concludes the author.