Cheating on your significant other is taboo in almost all cultures,
背叛另一半在几乎所有的文化中均被视为禁忌。
yet somehow adds flavor to the plot of movies and inspiration for countless songs about heartbreak.
不过不知怎地这种行为被用来为电影情节加料，同时也是无数苦情歌的灵感来源。
But why do people cheat in the first place?
但首先为什么人类会不忠呢？
Is there a science behind it?
我们能否给出科学的解释？
Only about 3% of mammals are monogamous, meaning they stay with one partner their whole life and humans fall into this category.
一夫一妻制仅仅存在于3%的哺乳动物中，这类包括了向往执子之手与子偕老的人类。
From an evolutionary perspective it creates an advantage where one partner can protect the younglings while the other searches for food and provides resources.
从进化观点上，这提供了一定的优势，夫妻中的一人得以保护后代，而其配偶则负责寻找食物，提供资源。
But somehow, extra-pair mating or cheating is a fairly common human behavior.
但出于某种原因，人类与配偶之外的对象交配或出轨行为是普遍存在的。
The gene coding for a dopamine receptor plays a key role in cheating for men and women.
人类出轨行为与多巴胺受体的基因编码有着重要的关系。
Sometimes call the ‘happy hormone’, it’s released after pleasurable activities like exercise, eating food, and orgasming.
有时被称为“快乐激素”，它在人类进行运动，进食，高潮等愉悦的活动后分泌。
And one study found that 50% of people who possess the long allele variant of this gene had cheated on their partner,
一项研究表明在该基因区拥有长等位基因的人中50%曾经背叛他们的伴侣。
compared to only 22% of people who have the short allele.
相比之下，仅有22%的拥有短等位基因的人出轨。
The long allele participants also had a tendency to be risk-takers and succumb to addictive behaviors such as alcoholism.
这些长等位基因拥有者也更倾向于承担风险，并更容易沉湎于诸如酗酒之类的成瘾行为。
Perhaps the phrase ‘once a cheater, always a cheater’ may have a basis in reality.
或许一次出轨，终生出轨的说法的确有其现实依据。
Levels of the hormone vasopressin also play a role.
后叶加压素同样能够起作用。

Similar to oxytocin, which is sometimes called the ‘cuddle hormone’ vasopressin can affect trust, empathy and social bonding.
与俗称“熊抱激素”的催产素类似，后叶加压素能够影响人与人间的信任，同感能力及社交关系。
In fact, injecting vasopressin directly into a polygamous montane vole’s reward centre increases the likelihood of it becoming monogamous!
事实上，向拥有多个性伴侣的山地田鼠的奖赏中枢直接注射后叶加压素可以增加其忠于单一性伴侣的可能性。
People with autism also have lower vasopressin levels, affecting their ability to understand social cues.
自闭症患者通常也拥有偏低的后叶加压素水平，这影响了他们在社交中理解对方暗示的能力。
And in 2014 a study involving over 7000 Finnish twins found that cheating women had a variant in the gene that codes for a vasopressin receptor,
一项2014年对7000余对芬兰双胞胎的研究表明，出轨的女性后叶加压素受体的编码基因发生了变异，
further suggesting that low levels of vasopressin have an influence on cheating.
进一步阐述了后叶加压素水平低下与出轨行为间的联系。