Why do we have hair in such random places? - Nina G. Jablonski

譯者: 子容 黃 審譯者: Amanda Zhu

We have lots in common with our closest primate relatives.

我們與其他靈長類近親有許多共同點。

But comparatively, humans seem a bit... underdressed.

但相對而言，人類穿著 似乎有些……單薄。

Instead of thick fur covering our bodies,

我們沒有厚重的毛髮覆蓋身體，

many of us mainly have hair on top of our heads—

毛髮主要集中在我們的頭頂

and a few other places.

和其他幾個地方。

So, how did we get so naked? And why do we have hair where we do?

我們是怎麼變得這麼光禿禿的？ 我們的毛髮又為何會長在那些地方？

Human hair and animal fur are made of the same stuff:

人類毛髮和動物毛 是由同樣的材料做成的：

filaments of the protein keratin that grow out of organs known as follicles,

從稱為毛囊的器官中長出，

which go through cycles of growth and shedding.

經歷生長和脫落循環的角蛋白絲。

Across mammalian species, hairs have been modified for numerous purposes,

哺乳動物中，毛髮已演化出多種用途，

ranging from the soft fluff covering rabbits

從覆蓋兔子的柔軟絨毛

to the rigid quills protecting porcupines.

到保護豪豬的硬刺。

But for many mammals, hair grows in two layers

許多哺乳動物的毛髮生長為兩層，

consisting of a shorter undercoat of ground hairs

由較短的毛作為底層毛髮，

covered by longer guard hairs.

上面覆蓋較長的保護毛。

Together, they help insulate the animal’s body and protect its skin.

它們一起幫助動物的身體 與外界隔絕並保護其皮膚。

Human hairs, on the other hand, are kind of a combination of these hair types.

另一方面來說，人類的毛髮 綜合了這些類型的毛髮。

Unfortunately, hair is rarely found in fossils,

不幸的是，化石中鮮少發現毛髮，

making it hard for researchers to pinpoint when and how

使研究人員很難確定古代的祖先

our ancient ancestors lost their coats.

在何時以及如何失去他們的外衣。

But scientists have developed some working hypotheses.

但科學家們已提出一些現行的假說；

It seems that, millions of years ago in Africa,

似乎在數百萬年前的非洲，

early hominins first transitioned out of trees and adopted a more active lifestyle.

早期的古人類從樹居 轉型為活動性較高的地面生活，

Keeping cool became increasingly important.

因此保持涼爽變得越來越重要，

Eventually, they developed more sweat glands,

於是，他們發育出更多的汗腺，

which helped them lose heat by evaporating moisture through the skin.

以幫助他們透過皮膚蒸發水分來散熱。

In fact, humans have 10 times more sweat glands than chimpanzees, for instance.

事實上，舉黑猩猩為例， 人類的汗腺數量是它的 10 倍。

But efficiently losing heat by sweating is harder to do when you’re covered in fur.

但是當你被毛皮覆蓋時， 很難透過出汗有效地散熱。

Scientists believe that early humans lost much of their coat around this time

科學家認為，早期的人類 在這個時期失去了大部分毛髮

to help their sweat evaporate faster.

來讓汗水蒸發得更快。

However, if losing our hair was so advantageous,

然而，如果脫毛有如此好處，

why do we have any left at all?

我們為什麼還留著一些呢？

It seems that there are unique uses for hair in different parts of our bodies.

我們身體不同部位的毛髮 似乎都有其獨特的用途。

When it comes to the tops of our heads,

說到我們頭頂時，

temperature regulation likely played a part again.

溫度調節似乎又是個重點。

Since early humans began venturing into the open,

自早期人類開始進入 沒有樹木遮蔽的地區以來，

their heads would’ve been exposed to the scorching sun.

他們的頭部就會暴露在烈日下。

Thicker, longer-growing hair protects our sensitive scalps

長而濃密的頭髮 可以保護我們敏感的頭皮，

and keeps our brains from overheating.

並避免我們的大腦過熱。

Dark tightly curled hair is most effective at keeping solar radiation off of skin.

深色且極為捲曲的頭髮 最能有效地防止太陽輻射照射皮膚。

Other kinds of head hair evolved as humans moved to different places.

人類移居不同的地方時， 也演化出不同類型的頭髮。

Meanwhile, researchers think eyebrows are especially useful for communication

同時，研究人員認為眉毛 特別有助於溝通，

because they sit atop active facial muscles that convey our feelings.

因為它們位於表達 我們感受的面部肌肉上。

Eyelashes have been shown to minimize airflow over our eyeballs,

已有證據顯示睫毛可以 使我們眼球上的氣流降到最低，

preventing them from drying out and catching debris.

避免眼球乾燥並防止雜質進入。

And maybe facial hair proved helpful in distinguishing identity from a distance,

也許鬍子有助於從遠處分辨身份，

but we really don’t know.

但我們其實不確定。

Evidence is stubbly at best.

證據過於粗淺。

Why we have hair in other regions is... more pungent.

為什麼我們在其他部位 有毛髮的問題就更……辛辣了。

Our armpits, nipples, and pubic areas are dotted with apocrine glands.

我們的腋窩、乳頭和陰部 分佈著頂泌腺，

They produce oily, smelly secretions which the thick, curly hair

它們會產生油膩有臭味的分泌物，

that often grows in these spots helps disperse.

通常長在這些部位上的濃密捲髮 有助於散播這些分泌物。

The secretions that waft off these hairy patches may be useful for identification.

從這些毛髮部位飄出的分泌物 可能有助於識辨身分。

For example, several studies have shown that people are able to identify

舉例來說，多項研究顯示

人們能夠識別自己 以及親近的人的腋窩氣味。

their own armpit odors as well as those of people they’re close with.

The final type of notable human hair is the vellus hair that covers our bodies.

最後一種值得一提的人類毛髮是 覆蓋我們身體的毳毛。

We don't know if these hairs serve any purpose themselves,

我們不知道毳毛是否有任何用途，

but the follicles vellus hair grows from are essential banks of stem cells

但從長出毳毛的毛囊 是重要的幹細胞庫，

that repair damaged skin after injury.

能修復受傷的皮膚。

They’re also important sites of nerve endings that convey signals

它們也是神經末梢所在的重要部位，

of gentle touch to the brain.

向大腦傳遞溫柔觸摸的信號。

In fact, although it’s much finer,

事實上，儘管人類毛髮比人猿細得多，

humans have roughly the same density of body hair as apes of comparable sizes.

但人類的體毛密度 與體型相當的人猿幾乎相同。

So despite all this talk of human nakedness,

所以儘管有這麼多人類赤裸的說法，

we're not actually as hairless as we look.

我們實際上並不像看起來那麼無毛。