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Thanks to Brilliant for supporting this episode of SciShow. Go to Brilliant.org/SciShow to learn more.
感谢Brilliant对本期节目的支持。前往Brilliant.org/SciShow了解更多。
In 1896, painter and naturalist Abbott Thayer published a scientific paper with lots of illustrations of dead birds.
1896年，画家兼自然主义者雅培·泰勒发表了一篇科学论文，其中有很多死鸟的插图。
But in one of those pictures, he painted the bird's belly the same colors as the rest of its body.
但在其中一张照片中，他将鸟的腹部和身体其他部分画成了一种颜色。
And it stuck out like a sore wing. It was way easier to spot in its natural habitat. Thayer wasn't just a weirdo.
它像一只疼痛的翅膀很突出。在它的自然栖息地更容易找到。泰勒并不是一个怪人。
He wanted to answer a question that applies to a huge number of animals:
他想要回答一个适用于大量动物的问题：
Why do they have light-colored bellies and darker backs? But 123 years after his paper, we still don't actually know for sure.
为什么它们的腹部是浅色的，而背部是深色的？但在他的论文发表123年后，我们仍然不能确定其中的原因。
This pattern is called countershading, and you see it in everything from dogs to nautiluses.
这种模式被称为反荫蔽，并且你可以在各种生物，如狗狗和鹦鹉螺身上看到这种模式。
Thayer thought there must be something about countershading that helps animals survive; it's just too widespread to be coincidence.
泰勒认为反荫蔽模式在某种程度上一定是可以帮助动物生存的；这一现象太普遍了，所以不可能是巧合。
And he settled on two related ideas. First, sunlight makes dark backs look lighter than they are --
他有两个相关的想法。首先，阳光使深色的背部看起来比实际上要浅
so an animal's back ends up looking a lot like its lighter front.
所以动物背部看起来很像颜色较浅的前部。
Thayer thought that makes it harder to figure out where parts of an animal are just by looking at it --
泰勒认为这样一来，仅凭观察就很难确定动物身体的部位—
like, if you're a predator who wants to go for the throat.
比如，如果你是一个要想咬住它们喉咙的捕食者。
Second, he proposed that white bellies look like a sunlit sky, while dark backs look more like shadowy ground.
第二，他提出白色的腹部看起来像是阳光普照的天空，而黑色的背部看起来更像阴影笼罩的地面。
So from above and below, countershaded animals blend into the background.
因此，从上面到下面，反荫蔽动物可以融入背景。
Naturalists spent decades cataloguing examples that seemed to confirm Thayer's ideas.
自然学家们花了几十年的时间对似乎证实了泰勒观点的例子进行分类。
They saw countershading pretty much everywhere -- any place sunlight creates a lot of contrast.
他们几乎能在任何地方看到反荫蔽现象—任何阳光创造出了强烈对比的地方。
They didn't really find it in places with less sunlight -- like caves or the deep ocean. Seems pretty open and shut!
在阳光较少的地方，他们并没有发现这种现象—如洞穴或深海。似乎一切一目了然！
But over the last thirty years or so, biologists have pointed out that listing examples of countershading is different from proving why it happens.
但在过去三十年左右的时间里，生物学家指出，列举反荫蔽的例子与证明它为什么会发生是不同的。
They've been testing Thayer's ideas, like scientists are supposed to do. And their results have been… mixed.
他们一直在验证泰勒的观点，就像科学家应该做的那样。他们的结果喜忧参半。
One strategy is to present birds with fake insects, some countershaded and some uniformly colored.
一种方法是给鸟提供一些假的昆虫，一些是反荫蔽的，一些的颜色一样。
In some experiments, birds eat fewer countershaded insects. But in others, birds eat them all the same.
在一些实验中，鸟儿们较少食用反荫蔽的昆虫。但在其他实验中，鸟儿们照吃不误。
And some researchers find that countershaded mammals don't blend into all environments better
一些研究人员发现反之相比，反荫蔽哺乳动物并没有
than they would without countershading, like Thayer originally proposed.
更好地融入各种环境之中，这和泰勒最初起初的观点不一样。
Others say that in computer models, countershaded animals do blend in. And that's pretty much how it's gone.
其他人称，在电脑模型中，反荫蔽动物确实能够融入环境。并且大部分都是这样。
Whenever Thayer's ideas seem vindicated, they get called into question again.
每当泰勒的观点似乎被证明是正确的，它们就会再次受到质疑。
Meanwhile, people have proposed other hypotheses for how countershading can help animals survive.
此外，关于反荫蔽如何帮助动物生存，人们已经提出了其他假设。
Dark pigments tend to be better at blocking cell-damaging ultraviolet radiation,
深色色素更能阻挡对细胞有害的紫外线辐射，
so maybe animals evolved with more pigment where there's more sunlight.
所以动物们让能更多接触阳光的部分进化出了更多的这种色素。
But nobody's shown that countershaded animals suffer from increased UV exposure
但没有人证明，由于反荫蔽的消失，反荫蔽动物会更多的暴露在UV中
as a result of countershading going away -- like if they're albino or something.
比如它们有白化病或其他什么。
Dark pigments may also make some materials more wear-resistant, but the evidence for that is thin as well.
深色色素也可能使一些材料更耐磨，但这方面的证据也很薄弱。
So none of these hypotheses seem to cover it. Or maybe it has more to do with how dark pigments interact with heat.
所以这些假设似乎都不全面。又或者这与更多地与深色色素如何与热相互作用有关。
It could help animals stay warm.
这样可以帮助动物保暖。
Dark colors absorb more heat, and penguins turn their dark backs to the sun when they're cold.
深色吸收更多热，企鹅冷的时候，也会背部朝向太阳。
So maybe that's where their little tuxedos come from. Or it could help some animals stay cool under the right conditions.
也许这就是它们小礼服的由来。或者这样可以帮助一些动物在合适的条件下保持凉爽。
Experiments have shown that dark pigments are better at dispersing heat via the wind than light pigments.
实验表明，深色色素比浅色色素更善于通过风来分散热量。
There's even some evidence that this surface-level warmth thins air and water around countershaded animals, making swimming or flying easier.
甚至有一些证据表明这种表面能级温度可以疏散反荫蔽动物周围的空气和水分，让游泳或飞行变得更加容易。
In the end, it's possible that there's no one reason so many different animals have evolved countershading.
最后，有可能这么多动物进化出反荫蔽功能的原因各不相同。
Some animals likely had different evolutionary drivers than others -- even if their bodies ended up at the same solution.
有些动物可能具有不同于其他动物的进化驱动力—即使它们的身体最终得到了相同的解决方案。
So unfortunately for Abbott Thayer, and just-so explanations,
所以不幸的是，对于雅培·泰勒来说，只是这样的解释，
countershading is probably a little more complex than general-purpose camouflage.
反荫蔽功能可能比一般用途的伪装要复杂一点。
If complex answers to interesting questions are the sort of thing you enjoy, you might like the Daily Challenges over on Brilliant.
如果你喜欢有趣问题的复杂答案，你会徐会喜欢Brilliant的Daily Challenges。
They post multiple new challenge questions every day, covering everything from statistics to electricity to computer science.
他们每天都会发布多个新的挑战性问题，涵盖从统计学到电学再到计算机科学的方方面面。
Each challenge question gives you all the tools you need to solve it -- and if it really gets your wheels turning,
每一个挑战性的问题都会给你解决它所需的所有工具——如果它真的能让你转动脑筋，
each question also ties back to a whole interactive course you can take.
每个问题都有你可以参加的整个互动课程。
Premium members can access the whole archive of challenge questions --
会员可观看所有挑战问题—
and it just so happens that the first 200 people to sign up at Brilliant.org/SciShow will get 20% off an annual Premium subscription.
前200名注册Brilliant.org/SciShow的用户将享受年度会员八折优惠。
So check it out if you're interested, and thanks for your support.
感兴趣可以去看看，感谢大家的支持。
