你或许也会面对它(You might as well face it)
sex stimulates the release of vasopressin and oxytocin in people, as well as voles, though the role of these hormones in the human brain is not yet well understood. but while it is unlikely that people have a mental, smell-based map of their partners in the way that voles do, there are strong hints that the hormone pair have something to reveal about the nature of human love: among those of man's fellow primates that have been studied, monogamous marmosets have higher levels of vasopressin bound in the reward centres of their brains than do non-monogamous rhesus macaques.
other approaches are also shedding light on the question. in 2000, andreas bartels and semir zeki of university college, london, located the areas of the brain activated by romantic love. they took students who said they were madly in love, put them into a brain scanner, and looked at their patterns of brain activity.the results were surprising. for a start, a relatively small area of the human brain is active in love, compared with that involved in, say, ordinary friendship. “it is fascinating to reflect”, the pair conclude, “that the face that launched a thousand ships should have done so through such a limited expanse of cortex.” the second surprise was that the brain areas active in love are different from the areas activated in other emotional states, such as fear and anger. parts of the brain that are love-bitten include the one responsible for gut feelings, and the ones which generate the euphoria induced by drugs such as cocaine. so the brains of people deeply in love do not look like those of people experiencing strong emotions, but instead like those of people snorting coke. love, in other words, uses the neural mechanisms that are activated during the process of addiction. “we are literally addicted to love,” dr young observes. like the prairie voles.
it seems possible, then, that animals which form strong social bonds do so because of the location of their receptors for vasopressin and oxytocin. evolution acts on the distribution of these receptors to generate social or non-social versions of a vole. the more receptors located in regions associated with reward, the more rewarding social interactions become. social groups, and society itself, rely ultimately on these receptors. but for evolution to be able to act, there must be individual variation between mice, and between men. and this has interesting implications.last year, steven phelps, who works at emory with dr young, found great diversity in the distribution of vasopressin receptors between individual prairie voles. he suggests that this variation contributes to individual differences in social behaviour—in other words, some voles will be more faithful than others. meanwhile, dr young says that he and his colleagues have found a lot of variation in the vasopressin-receptor gene in humans. “we may be able to do things like look at their gene sequence, look at their promoter sequence, to genotype people and correlate that with their fidelity,” he muses.
it has already proved possible to tinker with this genetic inheritance, with startling results. scientists can increase the expression of the relevant receptors in prairie voles, and thus strengthen the animals' ability to attach to partners. and in 1999, dr young led a team that took the prairie-vole receptor gene and inserted it into an ordinary (and therefore promiscuous) mouse. the transgenic mouse thus created was much more sociable to its mate.
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