美貌是如何形成的？

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.俗話說，美貌不過是一張皮。這話不對。皮膚其實是很重要的（化妝品行業已證實），皮下的肌肉和骨骼也很重要。人的臉形尤爲關鍵，臉形由骨骼決定，對美貌有重要作用。從尋找伴侶角度看，美的全部意義在於誰長得漂亮，美貌的成因不僅爲審美問題，還是一個生物學問題，比如，骨骼結構的形成和它們傳達美的方式。

迄今，探究美貌生物學基礎的科學實驗，仍然離不開人的感官和實驗中的相關問題。一些研究結果有價值而不明顯，比如臉形對稱。

其中人類的繁殖實驗意義重大。人類繁殖使臉形一代一代傳承，從中可以分辨出後代臉形變體傳承父母美貌的成因，其中包括能育力、生產力、社會地位、現實的身體狀況和未來的身體免疫能力。許多現象都被看做美貌的因素，事實也是如此。不同的是，人類是兩性高級社會動物，配偶雙方共同撫育後代，或者至少有一方撫養。因此可能還有其他重要的影響因素，比如配偶平和的性格與和善的外貌。

雖然人類繁殖實驗難以實現，但劍橋大學人類生物學家艾琳·伊利亞耗費50年，最終完成了不同物種的繁殖實驗。伊利亞博士已將實驗分析結果發表在《生物學評論季刊》。實驗研究的動物是狐狸。

狡黠的狐狸

故事源於1959年的俄羅斯新西伯利亞。遺傳學家德米特里·貝爾耶夫做了一項實驗，他試圖馴化一批銀狐供農民使用，從中發現，狐狸表皮變爲斑狀，耳朵下垂，頭骨變小，面部變平，鼻樑下塌，下巴變短，牙縫變窄。

馴化的狐狸就像野狼被馴化成狗。貝爾耶夫把該選擇結果稱爲“友好行爲”，這種選擇既不令人害怕也沒有攻擊傾向，反之，樂於與人相處。

這種現象與激素有關，比如雌激素和神經傳遞素，它們會調節動物的生理行爲，對動物進化有重要影響。所以那些社會羣居物種行爲比較友好，因爲它們需要處理相互關係。以現代人爲例，結婚和生子時，看起來更“友好”，因爲這代表着積極的社會態度，伊利亞博士對此提供了大量證據。

男人喜歡什麼長相的女人，這一點大家都知道，研究這個似乎是多餘的。可以這麼說，受歡迎的一些面貌特徵就像貝爾耶夫馴化的狐狸一樣（扁平的臉、小鼻子、下巴短、頭蓋骨高度和臉長之間比例大）。那些顱面部比例大的人通常被認爲是文化修養高的人。

更可笑的是，他們把外部特徵與父母對孩子的態度聯繫起來。至少有15項研究顯示漂亮的孩子更招媽媽待見。其中至少有一項表明這種偏見從孩子出生時就存在。

一些相關細節出人意料。一名研究員花了十年觀察媽媽購物時如何照看孩子，發現在被評爲不漂亮的孩子中，只有1%得到細心照料，而漂亮的孩子中這一比例爲13%。另一研究員發現長期遭受虐待的孩子顱面比值比較小。

自然狀態下，這種行爲漸漸消失，廣泛被接受的臉形，我們稱之爲“美”。如果這種特徵被認定爲友好的社會行爲，這種行爲也會不斷擴大。

伊利亞博士的傾向性假設已被證實存在。33項研究表明漂亮的孩子更能適應社會，更受歡迎，智商更高，社交能力也更強。當然，這些人也更容易找到對象，育嬰率也高。其中一項研究發現相對漂亮的女士育嬰率要高出16%；相對英俊的男士繁殖率也會高出13%。

他人眼中的美

審美力是天生的——伊利亞博士的假設就是以此爲標準。嬰兒剛出生時的喜好決定了將來的審美觀念，這沒有性別、種族和認識對象的差別。

人類越長越漂亮——美在朝着人所期待的方向進化。復原的早期人類面部已證實這一點。兇殺案中，有時會根據對死者的描述，復原死者面貌，這可以證明早期人類面貌復原的真實性。

這些研究都不能完全證明伊利亞博士的假說。但這個假說貌似挺有道理的。如果她的假設正確，那麼美貌就不再是偶然獲得的特質，而是積極的社會行爲選擇的結果，美貌成了這種行爲的可靠標記。這種選擇包含兩個方面，一是漂亮的小孩成長更順利，一是漂亮的人會生育更多小孩。直面這個現實吧。