A glance through the personal ads in the newspaper confirms what most of us might have been expecting when it comes to seeking out the perfect partner: one study of 1000 such advertisements in the USA found that indicators of high fertility and good resources — like physical appearance, age and financial status — were frequent, and are major players in the decisions we make. This makes sense; other species go by similar cues that maximise healthy offspring, and therefore the amount of the parent’s genes that make it to the next generation. But some common preferences that the Lonely Hearts column throws up seem to have no relation to reproductive success, and don’t come into the equation at all in other species. What are these quirks, and what makes us humans buy into them?
‘GSOH’ (a good sense of humour) is a popular trait in the dating stakes — mostly offered by men, and in high demand amongst women. In opposite sex interactions, men provoke the most laughter: even from a young age, silly schoolboys make girls giggle. The gender difference is enigmatic. After all, everyone likes a good laugh — it triggers the release of dopamine, a signalling chemical in the brain that makes us feel good. In most cultures, high-ranking individuals get the most laughs from their subordinates, a sign of power. It’s controversial, but this could explain why more women laugh at men in traditionally patriarchal societies like ours. On the other hand, laughter’s association with positive emotions could work to a female advantage; for example, nervous laughter from a woman on a first date can put a man at ease. But men should beware of trying this trick the other way round — nervousness is more common amongst women on a first date, and the unsubtle sound of laughter can increase tension rather than reduce it! A study of breastfeeding mothers suggests a more offbeat explanation: mothers of babies with eczema that breastfed after laughing at comedy films saw reductions in severity of the skin condition and increased calmness in their children. This is thought to be due to an increase in a sleep-regulating hormone called melatonin, which can be found in breast milk. A laid-back baby is inevitably less stressful to raise – an excellent reason to choose a funny partner.
Kissing: it may be love you think you’re sharing, but that’s not all. Scientifically speaking, a kiss is a veritable swap-shop for the billions of bacteria lurking in your mouth. Nice. So, why do we like a good kisser? Though our ancestors may have kissed, it’s unlikely that humans are genetically “programmed” for it — some cultures, such as the inhabitants of the island of Mangia in the South Pacific, don’t kiss at all, implying that it’s determined by culture. Bizarrely, Eskimo kisses in which only noses are rubbed together might give a clue as to why kissing evolved. Studies have demonstrated that women prefer the scent of men with different immune system proteins (called MHCs) to their own: the idea is that children with healthier immune systems result from mixing genes that govern MHC production in their parents — the more different, the better. Lip kissing may have just been a sensible progression from there; lips are full of nerve endings and kissing releases endorphins, the chemicals responsible for that warm, fuzzy feeling. Besides, try asking for a goodnight sniff with a straight face…
According to women, intelligence is almost always sexy. Although it makes for more interesting conversation, better jobs and higher earnings, it’s not immediately obvious what the biological basis for this preference is. Intelligent men may make better lifestyle decisions, such as eating healthily and exercising, making them attractive to women because their children are more likely to make the same self-preserving choices. But that can’t be the whole story; some intelligent people still make poor health choices, like smoking.
One recent study claims that intelligence might actually be an indicator of reproductive ability: detailed data from a survey of US Army veterans, containing measures of intelligence, as well as of sperm count and motility, showed that sperm quality (believe it or not) is higher in more intelligent men. Oddly enough, it makes sense. Even though brains might seem like a bizarre manifestation of reproductive success, some of the same genes are involved in controlling the production of healthy neuron and sperm components, such as polyunsaturated fatty acids (PUFAs), which may account for the correlation. Clever stuff.