Claws vs. nails - Matthew Borths

翻译人员: Carol Wang 校对人员: Jiasi Hao

Consider the claw.

今天我们来说说爪子。

Frequently found on four-limbed animals around the world,

世界上的很多动物长着爪子，

it’s one of nature’s most versatile tools.

它是自然界中用途最广的工具之一。

Bears use claws for digging as well as defense.

熊使用爪子进行挖掘和防御，

An eagle’s needle-like talons can pierce the skulls of their prey.

鹰的针状爪子可刺穿猎物的头骨，

And lions can retract their massive claws for easy movement,

狮子能收回爪子以方便活动，

before flicking them out to hunt.

狩猎时再把爪子伸出。

Even the ancestors of primates used to wield these impressive appendages,

甚至灵长类动物的祖先 也曾使用这些令人印象深刻的附肢，

until their claws evolved into nails.

直到它们的爪子演变成指甲。

So what in our evolutionary past led to this manicured adaptation,

那么，在我们过去的进化中， 是什么造成整齐指甲的适应性进化，

and what can nails do that their sharper cousins can’t?

哪些事指甲能做到， 而比它锋利的爪子却不行？

When nails first appeared in the fossil record around 55.8 million years ago,

指甲首次出现于 大约 5580 万年前的化石中，

claws had already been present for over 260 million years

而哺乳动物和爬行动物的祖先

in the ancestors of mammals and reptiles.

长着爪子的记录已逾 2.6 亿年。

But despite the gulf of time between their emergence,

尽管它们的出现时间相差很多，

these adaptations are both part of the same evolutionary story.

但是，这些适应性 是同一进化过程的一部分。

Both nails and claws are made of keratin—

指甲和爪子都由角蛋白组成——

a tough, fibrous protein also found in horns, scales, hooves and hair.

角蛋白是一种坚韧的纤维蛋白， 也存在于角、鳞片、蹄和头发中。

This protein is produced by a wedge of tissue called the keratin matrix.

称为“角蛋白基质”的组织层 负责生产这种蛋白质，

Rich in blood vessels and nutrients,

该蛋白工厂组织富含血管和营养，

this protein factory produces an endless stream of keratin,

生产出源源不断的角蛋白流，

which is tightly packed into cells called keratinocytes.

紧紧塞满了角质细胞。

These high-density cells give nails and claws their trademark toughness.

正是这些高密度细胞， 赋予了指甲和爪子坚韧特性。

Since nails evolved from claws,

因指甲由爪子进化而来，

both adaptations produce keratinocytes in the same way.

所以，两种适应方式 都以相同方式产生角质细胞。

The cells grow out from the matrix,

细胞从基质中长出来，

emerging from the skin where they die and harden into a water-resistant sheath.

露出皮肤即死亡， 然后硬化成防水鞘。

The primary difference between the two keratin coverings

两种角蛋白覆盖物的主要区别

is really just their shape,

实际上只是形状不同而已，

which depends on the shape of the bone at the end of the animal’s digits.

取决于动物手指（脚趾） 末端的骨骼形状。

In claws, the bed of keratinocytes conforms to a narrow finger bone,

长爪子的动物，是因为角质细胞 顺着狭窄指骨形成基底，

wrapping around the end of the digit and radiating outwards

进而环绕手指末端，

to form a cone-shaped structure.

并向外辐射而形成锥形结构。

Animals with nails, on the other hand, have much broader digits,

另一方面，长指甲的动物 其手指（脚趾）要宽得多，

and keratinocytes only cover the top surface of their wide bones.

角质细胞仅覆盖其宽骨的顶表面。

It’s possible that nails have simply persisted as a side effect

灵长类动物进化出更宽、 更灵巧的手指后，

of primates evolving wider, more dexterous fingers.

指甲只是意外的收获。

But given what we know about the habitats of our primate ancestors,

但是，鉴于我们 对灵长类祖先栖息地的了解，

it’s more likely that nails came with their own powerful advantages.

指甲可能更有强大优势。

High in the forest canopy where these primates lived,

灵长类动物栖息于林冠高处，

wide finger bones and expansive finger pads were ideal

宽手指骨和宽阔的指垫

for gripping narrow branches.

非常适合抓紧细小树枝，

And nails improved that grip even further.

指甲更增强了握持力。

By providing a rigid surface to press against,

通过可以压靠的硬性表面（指甲），

primates could splay out their pads to create even more contact with the trees.

灵长类动物可张开指垫， 增加与树木的接触面积。

Additionally, nails improved the sensitivity of their digits

此外，它们在攀爬时， 额外表面（指甲）能感知压力变化，

by providing an extra surface to detect changes in pressure while climbing.

从而提高了手指的敏感性。

This combination of sensitivity and dexterity

灵敏性和灵巧性的结合

gave our ancestors the precise motor control needed to snatch up insects,

为我们的祖先提供了 精确的运动控制能力，

pinch berries and seeds, and keep a firm grip on slim branches.

可捉昆虫、捏住浆果和种子， 并牢牢抓住纤细的树枝。

The evolution of nails and the evolution of opposable thumbs and toes

指甲的进化，

与可对捏的拇指进化 和脚趾的进化紧密相关。

are closely linked.

And when our ancestors moved down from the trees,

当我们的祖先 从树上搬迁到陆地生活时，

this flexible grasp enabled them to create and wield complex tools.

这种灵活的抓握能力 使它们能制造和使用复杂工具。

Even if it was possible for wide fingers to sport claws,

即使宽手指也可以掌控爪子，

their sharp points would’ve likely interfered

但尖锐的爪尖可能会干扰

with these primates’ regular tasks.

这些灵长类动物的日常工作。

Claws are ideal for piercing, puncturing, and hooking,

爪子适合穿透、刺破和钩住东西，

but their points make grabbing difficult, and potentially dangerous.

但爪尖使得抓取困难， 并且有潜在危险。

However, both claws and nails are used in some unexpected ways.

但是，爪子和指甲都有某些 意想不到的使用方式。

Manatees use nails to grasp their food,

海牛用指甲抓住食物，

and researchers think elephant toenails may sense vibrations

研究人员认为，大象的脚趾甲 或许能感知地面的震动，

in the ground to help them hear.

以帮助它们听见远处声音。

Meanwhile, some primates, like the aye-ayes of Madagascar,

同时，一些灵长类动物， 例如马达加斯加指猴，

have re-acquired claws.

又重新获得了爪子。

They use these extra-long appendages to tap branches and trunks,

它们用这些超长附肢 敲打树枝和树干的同时，

while listening for hollow sections with their bat-like ears.

用蝙蝠状耳朵倾听， 以寻找空心部位。

When they hear an opening, they burrow into the tree

当它们听到有空响时， 就用爪子挖开并探入树中，

and skewer grubs with their needle-like middle finger.

然后用针状中指把幼虫串起来。

We’ve only scratched the surface of all the incredible ways nails and claws

关于动物界令人不可思议的 指甲和爪子的使用方式，

are used throughout the animal kingdom.

我们本次只做了表面了解，

But as for which of these adaptations is better?

但至于哪一种适应进化更好，

That’s an answer we may never nail down.

我们可能永远也无法得出答案。