“They spoil every romance by trying to make it last forever”, so wrote Oscar Wilde of women, his words no doubt echoed in the thoughts of thousands of men trudging round Clinton’s Cards the day before valentine’s day. But it is an equally true (or untrue) for either sex. We humans are odd in many ways, not least for the curious way we live out our romantic lives. All of us, at some stage, will develop a bizarre infatuation with someone who we view through rose-tinted spectacles. Most of us will end up spending a long period of time with this person. As a species we a prone to “falling in love”, this makes us strange. Strong bonding between pairs of animals is not common, but it isn’t unknown. Probably less than 5% of species go in for monogamy, though many of these cases will feature ‘extra-pair copulations’; one or both partners often have a bit on the side. Monogamy also occurs in primates, in the gibbons (an ape) and some small monkeys. My personal vote for the most romantic animal goes to the Titi monkey; pairs will sit together on branches and entwine their tails. What makes human romantic behaviour even more odd is that we form strong bonds with our partners within very large, complex social groups. In almost all other monogamous mammals, outsiders are treated with at best distain but more often open aggression. One species with a comparable love life to us is the Gelada baboon which forms strong bonds within groups of hundreds of individuals. Gelada males actively avoid contact with other male’s females and get very jealous. But if a male gets attacked by a rival male, bonded females may fight back for her partner, even though she will be half the size of the offending male! So what drove the evolution of love? Oxford anthropologist Robin Dunbar suggests a combination of our big brains and avoidance of infanticide. We have brains that are roughly 6 times larger than we would expect for our body size, and brains take a long time to develop. They also pose a problem during birth, as any mother will testify. In fact we are born in what is effectively a premature state because if our brains developed for longer, they wouldn’t be able to fit out through what is normally a very small hole. This means babies need a lot of care and attention, Dunbar argues that one parent alone would not have been able to provide and protect their infant thus favouring the evolution of bi-parental care. In a slightly more sinister twist, this could have been helped out by male’s protecting their partner and child to prevent rival males killing the kid and running off with the mother. That explains the pair, why the bond? In a neat evolutionary trick, the intense feeling we get when we’re in love is thought to be caused by a similar mechanism as that which triggers ‘maternal instinct’. Maternal care is triggered by linking the dopamine reward system (hormones that make us feel good) to cues from the baby, the ‘new baby smell’ or the GooGoos and GaGas for example. So when a mother smells her baby, she’ll get a rush of endorphins and she will effectively get addicted to her baby because of it. The same system has been co-opted to help form these bonds between partners; hence the good feeling associated with being in love. Love is like a drug facilitating an addiction to your partner which in turn ensures you stick together long enough to get your child through to adulthood. This makes our unusual love life one of our most important acquisitions during our evolutionary history.