The science of love at first sight

By N.L. | CHICAGO

BIOLOGISTS believe that love is fundamentally a biological rather than a cultural construct. That is because the capacity for love is found in all human cultures and similar behaviour is found in some other animals, such as prairie voles. In humans the purpose of all the cravings, craziness and desire is to focus attention on the raising of offspring. Children demand an unusual amount of nurturing, and two parents are better than one. Love is a signal that both partners are committed, and makes it more likely that this commitment will continue as long as is necessary for children to reach independence. But what does science have to say about the notion of love at first sight?

In recent years the ability to watch the brain in action has offered a wealth of insight into the mechanics of love. Researchers have shown that when a person falls in love a dozen different parts of the brain work together to release chemicals that trigger feelings of euphoria, bonding and excitement. (These include dopamine, oxytocin, adrenalin and vasopressin.) It has also been shown that the unconditional love between a mother and a child is associated with activity in different regions of the brain from those associated with sexual, pair-bonding love.

Passionate love is rooted in the reward circuitry of the brain—the same area that is active when humans feel a rush from cocaine. In fact, the cravings, motivations and withdrawals involved in love have a great deal in common with addiction. Its most intense forms tend to be associated with the early stages of a relationship, which then give way to a calmer attachment form of love one feels with a long-term partner. This has a slightly different chemistry but still involves the reward centres of the brain. What all this means is that one special person can become chemically rewarding to the brain of another. Love at first sight, then, is only possible if the mechanism for generating long-term attachment can be triggered quickly. There are signs that it can be. One line of evidence is that people are able to decide within a fraction of a second how attractive they find another person. This decision appears to be related to facial attractiveness, although men also favour women with a waist-to-hip ratio of 0.7, no matter what their overall weight is. (This ratio may indicate a woman's reproductive health.)

Another piece of evidence in Cupid's favour comes from work by Ayala Malack-Pines, a psychologist at Ben-Gurion University in Israel, who found in a survey that a small fraction (11%) of people in long-term relationships said that they began with love at first sight. In other words, in some couples the initial favorable impressions of attractiveness triggered love which sustained a lengthy bond. It is also clear that some couples need to form their bonds over a longer period, and popular culture tells many tales of friends who become lovers. One might also speculate that if a person is looking for a partner with traits that cannot be quantified instantly, such as compassion, intellect or a good sense of humour, then it would be hard to form a relationship on the basis of love at first sight. Those more concerned only with visual appearances, though, might find this easier. So it appears that love at first sight exists, but is not a very common basis for long-term relationships.

Dig deeper:
Hormones, attachment and why prairie voles fall in love (February 2004)
A philosopher and a biologist consider the science of love and betrayal (April 2012)
How "assortative mating" increases the gap between rich and poor (February 2014)