A kiss is not just a kiss
Science reveals how Bogart and Bergman didn’t get it right in Casablanca
Humans are hard-wired to favour leaning to the right while kissing romantic partners, an international study by psychologists and neuroscientists has found.
The research, by the universities of Dhaka, Bath and Bath Spa, also found that recipients of kisses had a tendency to match their partners’ head-leaning direction.
Experts built on work from western countries to investigate kissing behaviours in a non-western context, including a bias for turning the head to one side.
Their work, published in the journal Scientific Reports, studied 48 married couples in Bangladesh, where romantic kissing is not typically observed in public.
Couples were asked to kiss privately in their homes, then independently report back on various aspects of the kiss. Men were about 15 times more likely to initiate kissing than women, and both partners showed a bias for turning their heads to the right.
Dr Rezaul Karim, from the department of psychology at the University of Dhaka, said: “This is the first study to show sex differences in the initiation of kissing, with males more likely being the initiator, and also that the kiss initiators’ head-turning direction tends to modulate the headturning direction in the kiss recipients.”
The study found that more than twothirds of kiss initiators and kiss recipients turned their heads to the right. Men accounted for 79% of the kiss initiators.
A person being left- or right-handed predicted their head-leaning direction if they initiated the kiss. The head-leaning direction of the initiator also strongly predicted the head-leaning direction of the recipient. This suggests recipients tend to match their partners’ direction to avoid the discomfort of mirroring heads.
“This further suggests the underlying cognitive mechanisms of the act of kissing and head turning,” the authors said. “Though this action tends to be performed intuitively, a decision must be made about the direction to which the partners should lean to kiss each other.”
Kissing in Bangladesh is private and censored from television or film, precluding the influence of cultural factors such as copying actors, they added. Previous studies have involved couples kissing in public places such as airports or stations.
Dr Michael Proulx, from the department of psychology at the University of Bath, said: “This study is unique in giving us a look into a private behaviour in a private culture with implications for all people. Prior works could not rule out cultural learning due to having western samples. It turns out, we as humans are similar even if our social values differ.”
The research suggests the act of kissing is influenced by the way the brain divides tasks between its hemispheres, with the emotion and decision-related areas of the brain in the left cerebral hemisphere. Hormone levels, such as testosterone, might be unevenly distributed in each hemisphere, causing a bias to turn right.
It is hoped the findings will feed into further studies of neurophysiological mechanisms of such behaviours.
George Peppard and Audrey Hepburn kiss in the film Breakfast at Tiffany’s