Romance is in the air as Valentine's Day approaches, but as you pucker up for a kiss, which way do you turn your head?

A German researcher, who has observed over 120 couples kissing, found twice as many turn their heads to the right as to the left.

The habit could be dictated by the tendency of babies in the womb to turn their heads to the right.

Professor Onur G�nt�rk�n from Ruhr Universit�t, Bochum, in Germany said: "There could be one very early habit given to humans before birth which still influences our behaviour for the rest of our life and is visible in subtle habits during, for example, kissing."

I'm pretty sure that the romance doesn't depend on kissing direction Onur G�nt�rk�n

He observed couples aged from their teens to their 70s kissing in public, at airports, railway stations, beaches and ports.

Professor G�nt�rk�n studied couples in the US, Germany and Turkey to ensure he looked at people from a variety of cultural backgrounds.

He studied how they angled their heads for the initial kiss, which had to include lip contact and face-to-face positioning.

He also looked to see if the kissers were holding any objects in their hands, which he said could have influenced which side a person leaned to.

Mental abilities

Professor G�nt�rk�n was looking at kissing to try to understand why human brains function asymmetrically, with each side controlling different abilities.

He said the bias towards right-sided kissing could not be related to being left or right-handed, as right-handed people outnumber left-handed by around eight to one.

But the two to one ratio of right to left is also seen in more general bias when people have to choose which foot, eye or ear to use.

His finding mirrors the bias babies show in the womb during the final weeks of gestation, and in the first six months after birth to turn their heads to the right.

In birds, a preference for turning the head to the right before hatching has been seen to induce differences between the left and right sides in terms of motor, visual and cognitive ability control.

He suggests the same may be true for humans, with embryos tendency to lean to the right "igniting" the functional differences between the two sides of the brain.

Subtle habit

Professor G�nt�rk�n said he believed this right-sided preference never disappears, which was why he studied people kissing.

He said: "This result indicates that adults have a head-turning bias towards the right side, just like newborn babies.

"I fear that I have no news for lovers. I'm pretty sure that the romance doesn't depend on kissing direction.

"But kissing is one of those subtle habits that tell us something about the very dawn of us."

But Professor Chris McManus of University College London, said the research was unsurprising.

"Ninety per cent of babies, if you lie them on their back, turn their head to the right and stick out their left arm. It's a reflex."

The research is published in the journal Nature.