1.Only you: Human lips are different from those of all other animals because they are everted, meaning that they purse outward.
1.人类的嘴唇是外翻的，这一点和所有其他动物都不一样。

2.But we are not the only species to engage in kissing-like behaviors. Great apes press their lips together to express excitement, affection, or reconciliation.
2.但人类并不是唯一一个会做出“接吻”行为的物种。类人猿（包括大猩猩、黑猩猩、长臂猿等）在表达兴奋、喜爱或和解的时候也会将彼此的嘴唇贴在一起。

3.Scientists are not sure why humans kiss, but some think the answer lies in early feeding experiences. Through nursing and (in some cultures) receiving pre-chewed food from a parent's mouth, infants may learn to associate lip pressure with a loving act.
3.科学家们并不确切知道人类为什么要接吻，但一些人认为接吻行为和早期哺乳经历有关。通过哺乳——在一些文化中母亲还会将嚼碎的食物嘴对嘴喂给婴儿——婴儿可能学会了将嘴唇接触和表达爱意联系起来。

4.Another possibility: Smelling a loved one's cheek has long served as a means of recognition in cultures around the world, from New Zealand to Alaska. Over time, a brush of the lips may have become a traditional accompaniment.
4.另一种可能是：在世界各地——从新西兰到阿拉斯加——嗅闻所爱之人的脸颊一直都是表达认可的一种方式，久而久之，可能就伴随着发展出了碰触嘴唇这样一种传统礼仪。

5.And yet kissing is not universal, leading some experts to think it might actually be a learned behavior.
5.但接吻行为也并不是全球通行的，因此有一些专家认为它可能是一种后天习得的行为。

6.The Roman military introduced kissing to many non-kissing cultures; later it was European explorers who carried the torch.
6.古罗马军队将接吻行为带到了许多没有这种传统的文化中；后来欧洲的探险家们又将它带到了新大陆。

7.Being close enough to kiss helps our noses assess compatibility. In a landmark study, biologists reported that women prefer the scents of men whose immunity-coding genes are different from their own. Mixing genes that way may produce offspring with a stronger immune system.
7.在近到足够接吻的距离下，我们的鼻子能够判断对方是否适合相处。在一项里程碑式的研究中，生物学家们发现女人能够靠气味识别出那些免疫系统编码基因与自己不同的男人，从而影响她们对伴侣的选择，因为混合的基因可以让后代拥有更强的免疫系统。

8.Love Is the Drug: Dopamine, a neurotransmitter associated with feelings of desire and reward, spikes in response to novel experiences, which explains why a kiss with someone new can feel so special.
8.多巴胺是一种神经递质，负责传递欲望和兴奋等感觉，在经历新事物的时候活动最为强烈。这就可以解释为什么跟某个新认识的人接吻感觉如此不同。

9.In some people, a jolt of dopamine can cause a loss of appetite and an inability to sleep, symptoms commonly associated with falling in love.
9.对某些人来说，少量多巴胺就会引起食欲下降和失眠，而这些症状通常被当做坠入爱河的征兆。

10.Holding hands and kissing reduces levels of the stress hormone cortisol, thereby lowering blood pressure and optimizing immune response.
10.牵手和接吻可以降低“压力荷尔蒙”皮质醇的水平，因此可以降低血压和提高免疫反应。

11.And a passionate kiss has the same effect as belladonna in making our pupils dilate.
11.一个深情的吻可以和颠茄（一种有毒植物）一样让人的瞳孔扩大。

12.Prelude to a Kiss: Two-thirds of all people turn their head to the right when kissing. This behavior may mirror the head-turning preference observed in babies and even in fetuses.
12.三分之二的人在接吻时会将头转向右边。这和婴儿甚至胎儿在转头时的偏好是一致的。

13.Evolutionary psychologists have discovered that men are far more likely to prefer sloppy tongue kisses than women.
13.进化论心理学家发现，男人比女人更喜欢湿乎乎的舌吻。

14.Always brush and floss, boys. Evolutionary psychologists found that when deciding whether to kiss someone, women pay much closer attention than men do to the breath and teeth of their partner.
14.进化论心理学家还发现，在决定是否要同一个人接吻时，女人会比男人更加注意对方的呼吸和牙齿。所以小伙子们，记得好好刷牙。

15.You Give Love a Bad Name: One milliliter of saliva contains about 100,000,000 bacteria.
15.但是无论如何，一毫升唾液中还是有大约10亿个细菌。

声明：双语文章中，中文翻译仅代表译者个人观点，仅供参考。如有不妥之处，欢迎指正。