经济学人下载:进化和表皮色彩

Science and technology
科学与技术

Evolution and coat colour
进化和表皮色彩

Well spotted
美丽涂鸦

The reason why some cats are plain and others are patterned
为何有些猫科动物全无斑纹，而其他的则斑斑点点？

How the leopard got his spots is, famously, the subject of one of Rudyard Kipling's “Just So Stories”.
美洲豹为何满身斑点？这是吉卜林大作《原来如此》中的一个著名问题。

Kipling suggested they were handprints made by the leopard's human friend. More plausibly, he had an explanation for what the spots are for: to break up the animal's shape when it is hiding in the dappled light of the forest.
吉卜林认为，那是美洲豹的人类朋友们留下的手印。他更靠谱的解释是，当美洲豹藏身在树丛的斑驳光影之中，斑点有助于让它们“隐去”形迹。

These days, the human-handprint theory of the leopard's spots has fallen out of favour.
最近，美洲豹斑点的手印理论已不合口味。

Instead, a more prosaic idea has gained ground, based on what is known as reaction-diffusion pattern formation, in which chemicals that trigger the differentiation of cells in an embryo interact with one another to produce patterns that are then reflected in the fates of nearby cells.
取而代之并渐为人知的是一种更乏味的观点：斑点产生于“反应－扩散”的图案形成过程，其中，胚胎细胞分化由化学反应引发，各类化学反应之间又发生作用，其作用模式最后在表皮细胞的发育中表现出来。

But that, too, has its difficulties. Just how much a process like this can be shaped by natural selection is unclear.
但这一说也有其困难，它在多大程度上收到自然选择的影响，目前尚不清楚。

Reaction-diffusion patterns which can be created in a laboratory using standard reagents are simple and deterministic.
反应－扩散模式可在实验室用标准试剂产生简洁而又有说服力。

That simple reactions of this sort sometimes result in cryptic patterns could be a coincidence.
这类偶尔引发神奇图案的简单反应纯粹是巧合。

Nevertheless, the details of the patterns produced vary, according to things like how rapidly the chemicals diffuse.
不过，图案产生的细节各各不同，依据诸如扩散速度等情形而有差别。

That could be selected. Different cats do, indeed, have different patterns.
这就可加以选择。确实，不同的猫科动物有不同图案。

So researchers at the University of Bristol, led by William Allen, have been deconstructing these patterns, trying to match the elements to cats' habits and habitats, and thus show whether the patterns are evolving.
因此，在威廉姆﹒艾伦的带领下，布里斯托大学的研究者正在分解这些图案，并尝试把图案要素同猫科动物的习性与栖息地匹配起来，以发现图案是否会发生进化。

They published their results this week in the Proceedings of the Royal Society.
本周他们在《皇家学会学报》上发表了研究结果。

The reaction-diffusion process can be mimicked by a computer, and the program's parameters manipulated to produce patterns matching those of cat coats.
反应－扩散过程可以用计算机加以模拟，对程序参数也可加控制，以产生同猫科动物外表匹配的图案。

That, the researchers hoped, might help illuminate what is going on.
研究者希望借此搞清楚到底发生了什么。

They trawled the world wide web for pictures of wild cats, found the best six for each of 37 species, and roped in a group of human volunteers to choose which of the program's outputs were most similar to real coats.
他们在互联网上搜罗野生猫科动物的图片，为37个猫科物种的每一种都准备了最佳的6张照片，并说服一批人类志愿者来判定：哪个程序的输出结果和真实的外表最为相似。

The patterns produced had five parameters: how plain they were, how irregular, how complex, how big the spots were and whether the pattern had a perceptible direction to it.
为产生图案设置了5个参数：斑点的有无程度、规则程度、复杂程度、大小程度、是否有明显的生长位置。

The volunteers' judgments about which artificial patterns best matched which natural ones were almost perfectly consistent.
志愿者关于人工图案与自然图案匹配程度的判断几乎完美的一致。

That allowed Mr Allen to assess which parameters contribute to each species's pattern, and thus which are correlated with behaviour.
这使艾伦先生可以推断哪个参数对物种的图案起了影响，从而进一步同物种行为联系起来。

The biggest distinction—no surprise, but nice to confirm—is that spotted cats are forest cats and plain ones prefer open countryside.
最大的区别发现本身并不出人意料，但推理非常严密是：有斑点的猫科动物生活在丛林中，没有斑点的更偏好生活在开阔的平原地带。

In that, Kipling was right.
在这点上，吉卜林是对的。

An analysis based on the relationship between the species, though, shows that evolutionary lines can swap from spots to no spots, and vice versa, as the habitat dictates.
基于物种关系的一个分析表明，进化路线有时是从有斑点到无斑点，有时又反过来，这取决于栖息地在哪里。

Moreover, the more a species prefers the forest, the more irregular the pattern it sports, and the more complex.
并且，如果一个物种越是喜欢丛林生活，图案就越是不规则，越加复杂对大小和图案生长位置没有影响。

Size and direction have no effect.Even among forest-dwellers there are differences.
即使丛林物种之间也不一样。

Those that tend to spend their time actually in trees, as opposed to wandering around on the ground between them, have more irregular and complex patterns.
与那些喜欢呆在地上的相比，更多时间呆在树上的种群，其图案就更不规则，更加复杂。

And, crucially, there is no relationship between a cat's pattern and how sociable it is.
并且，重要的是在猫科动物的图案和社群习性之间没有关联。

That knocks on the head an alternative explanation for coat patterns, namely that spots are some form of signal between animals of the same species.
这对关于表皮图案的另一理论解释是当头一击，此种解释认为斑点是同一动物种群的共有标记形式。

Mr Allen and his colleagues made one other observation. Some species of cat regularly produce melanic forms—the so-called black panther actually a melanic jaguar being the most familiar.
艾伦先生及其同事还作了其他的观察。某些猫科动物会周期性变成黑色——例如大家熟悉的黑豹实际上是黑色的美洲虎。

The data seem to rule out one obvious explanation for melanism: the idea that black cats, with their unusual appearance, have more success hunting because their prey are not keeping an eye out for predators that look like them.
这一观察似乎也排除了“黑变论”的解释。这种说法是，黑色猫科动物因其不同寻常的外表，而在捕猎方面非常成功，因为它们无须留神被猎物看见。

Melanic forms, though, are particularly prevalent in species with complicated lives—those that inhabit a range of habitats, are active both day and night, and move between the ground and the trees.
可是，黑色外表为各种复杂形式的物种所有，它们栖息在不同地带、有白天活动的也有黑夜活动的、有在地面生存的也有在树上生存的。

What advantage melanism brings in these circumstances is obscure.
在这些环境中表皮黑化到底有什么优势似乎模糊不清。

One for Kipling, perhaps. “How the jaguar got his melanocytes.”
这问题可能要交给吉卜林了：“美洲虎为何是黑色？”