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.

雖然抗利尿激素和催產(chǎn)素在人腦內(nèi)的角色仍未被透徹了解，但與田鼠一樣，人體在受到性刺激時(shí)也會(huì)釋放這些荷爾蒙。盡管與田鼠不一樣，人類(lèi)不太可能有一張基于嗅覺(jué)的神經(jīng)系統(tǒng)伴侶圖譜，但若干線(xiàn)索已有力說(shuō)明，這兩種荷爾蒙能揭示一些人類(lèi)戀愛(ài)的本質(zhì)∶在已被研究過(guò)的人類(lèi)靈長(zhǎng)目同伴之中，一夫一妻制小長(zhǎng)尾猴的大腦獎(jiǎng)賞中樞系統(tǒng)中，抗利尿激素水平較非一夫一妻制的恒河短尾猿高。

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.

其他方法也正在為人們尋找這些問(wèn)題的謎底。2000 年，來(lái)自倫敦市大學(xué)學(xué)院的Andreas Bartels和Semir Zeki定位出了能被浪漫愛(ài)情激活的大腦區(qū)域。兩位學(xué)者選擇自稱(chēng)正在熱戀的學(xué)生作為測(cè)試目標(biāo)，利用腦掃描儀對(duì)他們的大腦活動(dòng)模式進(jìn)行觀測(cè)。

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.

令人驚訝的是：首先，人腦參與到戀愛(ài)的活動(dòng)區(qū)域，較之其他感情（如普通友誼），相對(duì)要比較小些。“引人注意的是，結(jié)果顯示，”兩位學(xué)者推斷說(shuō)，“美麗的面容是通過(guò)控制一個(gè)有限區(qū)域的大腦皮層來(lái)實(shí)現(xiàn)‘一顧傾人城，再顧傾人國(guó)’的。”  第二個(gè)驚奇之處是，大腦內(nèi)因戀愛(ài)而活躍的區(qū)域不同于因其他情緒而活躍的區(qū)域，例如，恐懼和憤怒。 被戀愛(ài)“咬住”的那部份大腦還包括負(fù)責(zé)內(nèi)臟感覺(jué)和因可卡因等毒品生成快感的區(qū)域。因此，因此，深墜愛(ài)河的戀人們的大腦，并非類(lèi)同于經(jīng)歷強(qiáng)烈情緒波動(dòng)的人，倒更接近那些鼻吸可卡因的癮君子。換句話(huà)說(shuō)，愛(ài)情使用的是在成癮過(guò)程中被激活的神經(jīng)機(jī)制。“嚴(yán)格地講, 我們成癮于愛(ài)情，”Young博士評(píng)述道，“就如同草原田鼠”。

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.

那么看起來(lái)，能形成穩(wěn)固社會(huì)聯(lián)結(jié)的動(dòng)物之所以愿意建立彼此間的伙伴關(guān)系，可能是由它們的抗利尿激素和催產(chǎn)素受體在大腦中的位置所決定。生物進(jìn)化作用于以上受體在大腦的分布，而產(chǎn)生了社會(huì)性或非社會(huì)性不同版本的田鼠。位于獎(jiǎng)賞機(jī)制有關(guān)區(qū)域的受體越多，對(duì)個(gè)體而言, 社會(huì)互動(dòng)就更具有回報(bào)性。動(dòng)物的社會(huì)性團(tuán)體，乃至整個(gè)社會(huì)本身都最終依賴(lài)于這些受體。但要使進(jìn)化真能發(fā)生效力，在鼠之鼠之間以及人與人之間，一定存在個(gè)體變異。這一論述還有引人入勝的推論。

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.

在Emory大學(xué)與Young博士一同工作的Steven Phelps去年發(fā)現(xiàn)，草原田鼠各個(gè)體間抗利尿激素受體的腦內(nèi)分布，存在著很大的差異。他提出，正是這一變異導(dǎo)致了社會(huì)行為的個(gè)體差異，換句話(huà)說(shuō)，一些田鼠將會(huì)比另一些更加忠誠(chéng)。同時(shí)，Young博士說(shuō)他和同事已經(jīng)發(fā)現(xiàn)人類(lèi)抗利尿激素受體基因的許多變異。“我們或許能夠做些類(lèi)似于察看人們的基因序列，察看他們的啟動(dòng)序列等工作，在此基礎(chǔ)上對(duì)人們進(jìn)行基因型分類(lèi), 并把分類(lèi)結(jié)果與他們的忠誠(chéng)度關(guān)聯(lián)起來(lái)”，Young博士作如是想。

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.

事實(shí)已經(jīng)證明可能對(duì)這種基因遺傳進(jìn)行修補(bǔ)，并產(chǎn)生了令人吃驚的結(jié)果。科學(xué)家能增加草原田鼠相關(guān)受體的表達(dá)，以加強(qiáng)動(dòng)物對(duì)同伴的依附能力。而且在 1999 年，Young博士帶領(lǐng)了一只研究隊(duì)伍，他們將草原田鼠的受體基因插入到一只平常(因此成為雜亂的) 老鼠的體內(nèi)，由此產(chǎn)生的轉(zhuǎn)基因鼠對(duì)它的配偶表現(xiàn)得更為友善。