爱美之心，人皆有之

　　BEAUTY, the saying has it, is only skin deep. Not true. Skin is important (the cosmetics industry proves that). But so is what lies under it. In particular, the shape of people’s faces, determined by their bone structure, contributes enormously to how beautiful they are. And, since the ultimate point of beauty is to signal who is a good prospect as a mate, what makes a face beautiful is not only an aesthetic matter but also a biological one. How those bone structures arise, and how they communicate desirable traits, are big evolutionary questions.

　　Until now, experiments to try to determine the biological basis of beauty have been of the please-look-at-these-photographs-and-answer-some-questions variety. Some useful and not necessarily obvious results have emerged, such as that one determinant of beauty is facial symmetry.

　　But what would really help is a breeding experiment which allowed the shapes of faces to be followed across the generations to see how those shapes relate to variations in things that might be desirable in a mate. These might include fertility, fecundity, social status, present health, and likely resistance to future infection and infestation. Correlations between many of these phenomena and attributes of the body-beautiful have, indeed, been established. But in a pair-forming, highly social species such as Homo sapiens, you also have to live with your co-child-raiser or, at least, collaborate with him or her. So other things may be important in a mate, too, such as an even temper and a friendly outlook.

　　It would be impossible to do such a breeding experiment on people, of course. But as Irene Elia, a biological anthropologist at Cambridge, realised, it has in fact been done, for the past five decades, on a different species of animal. Dr Elia has published her analysis of this experiment in the Quarterly Review of Biology. The animals in question are foxes.

　　Foxy ladies, vulpine gents

　　The story starts in 1959, in Novosibirsk, Russia. That was when Dmitry Belyaev, a geneticist, began an experiment which continues to this day. He tried to breed silver foxes (a melanic colour variant, beloved of furriers, of the familiar red fox) to make them tamer and thus easier for farmers to handle. He found he could, but the process also had other effects: the animals’ coats developed patches of colour; their ears became floppy; their skulls became rounded and foreshortened; their faces flattened; their noses got stubbier; and their jaws shortened, thus crowding their teeth.

　　All told, then, these animals became, to wild foxes, the equivalent of what dogs are to wild wolves. And this was solely the result of selection for what Belyaev called “friendly” behaviour—neither fearful nor aggressive, but calm and eager to interact with people.

　　The link appears to be hormonal. Hormones such as estradiol and neurotransmitters such as serotonin, which regulate behaviour, also regulate some aspects of development. Change one and you will change the other. So in a species where friendliness is favoured because that species is social and the group members have to get on with each other—a species like Homo sapiens, for example—a “friendly” face is a feature that might actively be sought, both in mates and in children, because it is a marker of desirable social attitudes. And there is abundant evidence, reviewed by Dr Elia, both that it is indeed actively sought by Homo sapiens, and that it is such a reliable marker.

　　What men look for in the faces of women, and vice versa, is so well known that research might seem superfluous. Suffice to say, then, that features like those seen in Belyaev’s foxes (flat faces, small noses, reduced jaws and a large ratio between the height of the cranium and the height of the face) are on the list. People with large craniofacial ratios are, literally, highbrow.

　　More intriguingly, the presence or absence of such features skews parents’ attitudes to their offspring. At least 15 studies have shown that mothers treat attractive children more favourably than unattractive ones, even though they say they don’t and may actually believe that. At least one of these studies showed this bias is true from birth.

　　Some of the details are extraordinary. One researcher, who spent a decade observing how mothers look after young children in supermarkets, found that only 1% of children judged unattractive by independent assessors were safely secured in the seats of grocery carts. In the case of the most attractive the figure was 13%. Another researcher studied police photographs of children who had been abused and found such children had lower craniofacial ratios than those who had not been.

　　In a state of nature, this sort of behaviour would surely translate into selective death and thus the spread of the facial features humans are pleased to describe as “beautiful”. If such features do indicate a propensity to friendly, sociable behaviour, as they do in foxes, then such behaviours will spread too.

　　Crucially for Dr Elia’s hypothesis, they do indeed indicate such a propensity. Even as children, according to 33 separate studies, the attractive are better adjusted and more popular than the ugly (they also have higher intelligence, which assists social skills). And of course, they have less difficulty finding a mate—and as a result have more children themselves. One study found that the most beautiful women in it had up to 16% more offspring than their less-favoured sisters. Conversely, the least attractive men had 13% fewer than their more handsome confrères.

　　The beholder’s eye

　　An appreciation of what is “beautiful”， moreover, seems innate—as Dr Elia’s hypothesis requires it should be. Babies a few days old prefer pictures of the faces of people whom their elders would define as beautiful to those they would not, regardless of the sex and race of either the baby or the person in the photo.

　　People also seem to be more beautiful now than they were in the past—precisely as would be expected if beauty is still evolving. This has been shown by assessing the beauty of reconstructions of the faces of early humans. (Such reconstructions, sometimes used in murder cases where only skeletal remains of the victim are available, produce reliable depictions of recently dead people, so the assumption is that ancients really did look like the reconstructions made of them.)

　　None of this absolutely proves Dr Elia’s hypothesis. But it looks plausible. If she is right, facial beauty ceases to be an arbitrary characteristic and instead becomes a reliable marker of underlying desirable behaviour. It is selected for both in the ways beautiful children are brought up, and in the number of children the beautiful have. Face it.

　　俗话说，美貌不过是一张皮。这话不对。皮肤其实是很重要的(化妆品行业已证实)，皮下的肌肉和骨骼也很重要。人的脸形尤为关键，脸形由骨骼决定，对美貌有重要作用。从寻找伴侣角度看，美的全部意义在于谁长得漂亮，美貌的成因不仅为审美问题，还是一个生物学问题，比如，骨骼结构的形成和它们传达美的方式。

　　迄今，探究美貌生物学基础的科学实验，仍然离不开人的感官和实验中的相关问题。一些研究结果有价值而不明显，比如脸形对称。

　　其中人类的繁殖实验意义重大。人类繁殖使脸形一代一代传承，从中可以分辨出后代脸形变体传承父母美貌的成因，其中包括能育力、生产力、社会地位、现实的身体状况和未来的身体免疫能力。许多现象都被看做美貌的因素，事实也是如此。不同的是，人类是两性高级社会动物，配偶双方共同抚育后代，或者至少有一方抚养。因此可能还有其他重要的影响因素，比如配偶平和的性格与和善的外貌。

　　虽然人类繁殖实验难以实现，但剑桥大学人类生物学家艾琳·伊利亚耗费50年，最终完成了不同物种的繁殖实验。伊利亚博士已将实验分析结果发表在《生物学评论季刊》。实验研究的动物是狐狸。

　　狡黠的狐狸

　　故事源于1959年的俄罗斯新西伯利亚。遗传学家德米特里·贝尔耶夫做了一项实验，他试图驯化一批银狐供农民使用，从中发现，狐狸表皮变为斑状，耳朵下垂，头骨变小，面部变平，鼻梁下塌，下巴变短，牙缝变窄。

　　驯化的狐狸就像野狼被驯化成狗。贝尔耶夫把该选择结果称为“友好行为”，这种选择既不令人害怕也没有攻击倾向，反之，乐于与人相处。

　　这种现象与激素有关，比如雌激素和神经传递素，它们会调节动物的生理行为，对动物进化有重要影响。所以那些社会群居物种行为比较友好，因为它们需要处理相互关系。以现代人为例，结婚和生子时，看起来更“友好”，因为这代表着积极的社会态度，伊利亚博士对此提供了大量证据。

　　男人喜欢什么长相的女人，这一点大家都知道，研究这个似乎是多余的。可以这么说，受欢迎的一些面貌特征就像贝尔耶夫驯化的狐狸一样(扁平的脸、小鼻子、下巴短、头盖骨高度和脸长之间比例大)。那些颅面部比例大的人通常被认为是文化修养高的人。

　　更可笑的是，他们把外部特征与父母对孩子的态度联系起来。至少有15项研究显示漂亮的孩子更招妈妈待见。其中至少有一项表明这种偏见从孩子出生时就存在。

　　一些相关细节出人意料。一名研究员花了十年观察妈妈购物时如何照看孩子，发现在被评为不漂亮的孩子中，只有1%得到细心照料，而漂亮的孩子中这一比例为13%。另一研究员发现长期遭受虐待的孩子颅面比值比较小。

　　自然状态下，这种行为渐渐消失，广泛被接受的脸形，我们称之为“美”。如果这种特征被认定为友好的社会行为，这种行为也会不断扩大。

　　伊利亚博士的倾向性假设已被证实存在。33项研究表明漂亮的孩子更能适应社会，更受欢迎，智商更高，社交能力也更强。当然，这些人也更容易找到对象，育婴率也高。其中一项研究发现相对漂亮的女士育婴率要高出16%；相对英俊的男士繁殖率也会高出13%。

　　他人眼中的美

　　审美力是天生的——伊利亚博士的假设就是以此为标准。婴儿刚出生时的喜好决定了将来的审美观念，这没有性别、种族和认识对象的差别。

　　人类越长越漂亮——美在朝着人所期待的方向进化。复原的早期人类面部已证实这一点。凶杀案中，有时会根据对死者的描述，复原死者面貌，这可以证明早期人类面貌复原的真实性。

　　这些研究都不能完全证明伊利亚博士的假说。但这个假说貌似挺有道理的。如果她的假设正确，那么美貌就不再是偶然获得的特质，而是积极的社会行为选择的结果，美貌成了这种行为的可靠标记。这种选择包含两个方面，一是漂亮的小孩成长更顺利，一是漂亮的人会生育更多小孩。直面这个现实吧。

　　(译者 00superman 编辑 丹妮)