Humans are hard-wired to favour leaning to the right while kissing their romantic partners, scientists claim.
They found that kiss recipients tended to match their partners’ head-leaning direction.
Although they knew this was true in Western countries, they were not sure if it was human nature or the result of cultural influences such as films and TV.
So they studied how couples kissed in Bangladesh, where public displays of affection are frowned upon and intimacy on screen is heavily censored.
Psychologists and neuroscientists from the universities of Dhaka, Bath and Bath Spa studied 48 couples in Bangladesh, asking them to kiss at home, then report back independently.
Men were 15 times more likely to initiate kissing, and both partners showed a bias for turning their heads to the right. More than two-thirds of kiss initiators and recipients turned their heads to the right.
Whether someone was left or right handed predicted which way they leaned their head – but only if they initiated the kiss.
The study, in the journal Scientific Reports, found that the head-leaning of the kiss initiator also strongly predicted the recipient’s head-leaning direction.
This suggests recipients match their partners’ direction to avoid the awkwardness of kissing with heads leaning the same way.
Dr Michael Proulx, from the University of Bath, said: "It turns out we as humans are similar, even if our social values differ."
The research suggests that the act of kissing is determined by the brain splitting up tasks to its different hemispheres, similar to being either right of left handed.