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.

那么看起来，能形成稳固社会联结的动物之所以愿意建立彼此间的伙伴关系，可能是由它们的抗利尿激素和催产素受体在大脑中的位置所决定。生物进化作用于以上受体在大脑的分布，而产生了社会性或非社会性不同版本的田鼠。位于奖赏机制有关区域的受体越多，对个体而言, 社会互动就更具有回报性。动物的社会性团体，乃至整个社会本身都最终依赖于这些受体。但要使进化真能发生效力，在鼠之鼠之间以及人与人之间，一定存在个体变异。这一论述还有引人入胜的推论。

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大学与Young博士一同工作的Steven Phelps去年发现，草原田鼠各个体间抗利尿激素受体的脑内分布，存在着很大的差异。他提出，正是这一变异导致了社会行为的个体差异，换句话说，一些田鼠将会比另一些更加忠诚。同时，Young博士说他和同事已经发现人类抗利尿激素受体基因的许多变异。“我们或许能够做些类似于察看人们的基因序列，察看他们的启动序列等工作，在此基础上对人们进行基因型分类, 并把分类结果与他们的忠诚度关联起来”，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.

事实已经证明可能对这种基因遗传进行修补，并产生了令人吃惊的结果。科学家能增加草原田鼠相关受体的表达，以加强动物对同伴的依附能力。而且在 1999 年，Young博士带领了一只研究队伍，他们将草原田鼠的受体基因插入到一只平常(因此成为杂乱的) 老鼠的体内，由此产生的转基因鼠对它的配偶表现得更为友善。

Love, love me do / 爱我，真心地爱我

Scanning the brains of people in love is also helping to refine science's grasp of love's various forms. Helen Fisher, a researcher at Rutgers University, and the author of a new book on love*, suggests it comes in three flavours: lust, romantic love and long-term attachment. There is some overlap but, in essence, these are separate phenomena, with their own emotional and motivational systems, and accompanying chemicals. These systems have evolved to enable, respectively, mating, pair-bonding and parenting. ()