When two people fancy each other their heart rates jump in harmony

If you want someone to love you, forget body language - the real measure of whether two people are in love is the synchronization of their internal body functions, such as heart rate and sweating.

How to know if your partner is in love with you
"You often hear the famous phrase that people who fall in love produce sparks between them - we wanted to know if we could quantify these sparks," Mariska Kret of Leiden University in the Netherlands told a meeting of the European Primatology Federation in Oxford last week.

Kret's team investigated by setting up a booth at a music festival, where people could participate in brief one-on-one meetings with potential partners. They were allowed to look at the other person for two minutes and to have two more minutes to discuss.

The 140 people who took part in this contest were heterosexual, as only a few gay people volunteered and their cabin visits did not coincide with each other.

There is no body language to tell if the attraction is shared
Subjects were connected to sensors that measured their heart rate and skin conductivity and wore glasses that followed their gaze. In addition, all their body movements were recorded. At the end, they answered questions about their meeting, including whether they wanted to meet again and whether they thought their partner wanted to meet again,

The researchers found that there was no body language to predict whether or not people liked their partner - including the look, facial expressions, facial touch and agreement.

Sometimes people would reproduce the other person's behaviour - for example, by smiling or tilting their heads in the same way as the other person. But contrary to popular belief, there was no correlation between resemblance and sparks of attraction.

Sally Farley of the University of Baltimore says that this contradicts previous studies. "There are a large number of scientific studies that show that behaviors are predictive of attraction. Eye contact, proximity, touch, gestures, mimicry, voice are all behavioural indicators of attraction. »

Heart rate and skin conductance were synchronized
However, the Dutch team found that the more synchronized the heart rate and skin conductance of couples during their conversation, the more attracted they were to each other. "There was no body language to tell you if your partner was interested - physiology is where we found the best estimates," says Eliska Prochazkova, also from Leiden University.

People generally cannot control these internal functions," explains Prochazkova. "We cannot perceive the other person's heart. But often our subconscious can be influenced by our physiology. »

The team also found that people had difficulty measuring their partners' feelings. When asked to predict whether their partner would like to meet with them again, they did not score any better than by chance.

But the answers revealed a certain bias: if a person loved their partner, they were more likely to think they loved him or her, even if in reality there was no correlation. "People tend to be biased by their own feelings," explains Prochazkova.

There were differences between men and women
The researchers also found differences in the behaviour of men and women. Women smiled, nodded and touched their faces more often, while men looked more at their partners' heads and eyes. In addition, women were more demanding. Only 34% of women said they wanted a second meeting, compared to 53% of men.