If anyone could find the secret to a long and happy marriage, and bottle it, they would make a fortune. After all, there can be few of us who have not at one time or another been left stumped - and even in despair - by the vagaries of the human heart. Given the impenetrable nature of love, the recent findings of a scientist in Sweden are all the more surprising. No one would think to look at the genes of voles - a rodent that resembles a mouse, but with a stubbier body, a somewhat rounder head and a shorter tail - to find clues to a successful relationship. But Hasse Walum has done just that - and even he admits the results are surprising.
The PhD student at the Karolinksa Institute in Sweden found that a gene involved in pair bonding in prairie voles also indicates how stable a marriage partner a man is likely to be. Mr Walum and his co-researchers looked at a gene that causes the production of a receptor for vasopressin, a hormone found in the brains of most mammals. The more copies of a variant of this gene, called allele 334, that a man carried, the more likely it was that his marriage would be unstable.
In prairie voles, famous for the strength of their pair bonding, scientists have been able to influence the degree of monogamy by manipulating levels of vasopressin in the brain. "We're very happy that our findings are so consistent with the animal studies," says Mr Walum, who used data from a study of more than 550 twins and their partners or spouses. "I would say it's quite surprising because voles and humans are very different species, but sometimes evolution has similar ways of finding solutions in different species."
Only 15 to 16 per cent of men who had no copies or just one copy of allele 334 reported having had a marital crisis in the past year. However, among men who had inherited allele 334 from both parents, the figure was 34 per cent. The results, published in the Proceedings of the National Academy of Sciences of the US, also showed a statistical link between the number of copies of allele 334 a man had, and how strong a bond he felt with his partner.
Women married to men carrying one or two copies of allele 334 were, on average, less happy with their relationships than women married to men who did not have any copies of that form of the gene. These results, Mr Walum says, represent the first time that a specific gene has been linked to pair bonding in humans. However, before women rush down to their nearest science lab to DNA test their potential partners, Mr Walum cautions against overestimating the effect of the vasopressin receptor gene on pair bonding behaviour.
All the people in the study, he emphasises, have been in stable relationships for five years, so even carrying two copies of allele 334 does not make a man a bad prospect as a partner. "It doesn't really determine what kind of happiness a man will experience in a future relationship," he says. Also, the study seems to raise as many questions as it answers. Mr Walum admits that the results need to be replicated in different samples and that more research is needed to find out biochemically how the gene influences pair bonding.
Vasopressin is known to have an effect on two regions of the brain called the amygdalae, but an answer as to how the hormone exerts its effect on relationship behaviour is still some way away. "That part of the analysis - what it does in the brain - is a mystery," he says. "The association between the gene and behaviour - we really don't know about these things." But if a woman cannot study a man's vasopressin receptor to decide whether or not to go out with him, she can instead do what people have done since time immemorial - decide on the basis of looks.
If another recent study is anything to go by, she might like to get a tape measure out and see how wide her would-be companion's face is. Scientists at Brock University in Ontario, Canada, have found that a wider face tends to be linked with aggression. The researchers studied photographs of ice hockey players and found that those with wider-looking faces accrued more penalty minutes, which are most often given for aggressive behaviour.
Perhaps not coincidentally, the most penalised player in the history of professional hockey, Denis Bonvie, has a face that falls exactly into that category. Separately, when testing how college students behaved when using a computer game, they discovered that men with wider faces tended to be more aggressive, more often pushing buttons that let them steal points from an opponent. As with the vasopressin receptor study, the results were found with men but not with women.
Professor David Perrett from the School of Psychology at the University of St Andrews in Scotland says there is scientific evidence that links facial characteristics to personality. "You can take an educated guess at the personality," he says. "If somebody is always looking angry and hostile, it's a good bet they're going to be aggressive. If they are smiley, it's more likely they will be happy interacting with you."
This might seem obvious, but what is less clear is the degree to which associations between facial appearance and personality type are determined by genes. Prof Perrett says that while there are "well-known links" between levels of the male hormone testosterone, aggressive behaviour and facial structure, this does not necessarily imply a definite biological relationship between them. For example, if a boy develops more rapidly than his counterparts and therefore is large and possibly aggressive looking, if he in turn behaves aggressively it might be because of the way people respond to his looks, rather than any inherent personality tendencies.
"The way people react tends to shape [personality]. Even if you start with one kind of character, you can be shaped into another kind by the way people react," he says. "If someone perceives extra testosterone in a person, they will treat them differently - with deference. That will allow more dominant individuals to become more dominant." It could also turn, he says, someone with a reasonably placid nature into a more aggressive individual.
"If we think someone is aggressive and dominant, we may unwittingly help them to become assertive by being deferential to them," he explains. "People often try to polarise [the effects of] genes and the environment, but here you can say there's an interplay between the two." In any case, regardless of whether the effects at work are genetic or environmental, many of us are simply poor at making judgements about personality based upon looks.
"People who are more extrovert, they tend to be better at this - they have had more social contact," Prof Perrett says. dbardsley@thenational.ae