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为什么我们只有这几个部位有毛?

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

再短的毛发也会有阴影 ——弗朗西斯·培根爵士
We have lots in common with our closest primate relatives.
我们与近亲灵长类动物有许多相似之处
But comparatively, humans seem a bit… underdressed.
但相比之下 人类似乎有点……“毛不蔽体”
Instead of thick fur covering our bodies,
我们没有厚厚的毛发覆盖在身体上
many of us mainly have hair on top of our heads
我们中的大多数主要只有头顶
and a few other places.
好少数其他部位有毛发
So, how did we get so naked?
那我们的皮肤是如何变得如此裸露的呢?
And why do we have hair where we do?
为什么我们某些部位又有毛发?
Human hair and animal fur are made of the same stuff:
人的毛发和动物的毛发构成都是一样的
filaments of the protein keratin that grow out of organs known as follicles,
都是从毛囊的器官中生长出来的角蛋白丝
which go through cycles of growth and shedding.
它们经历了生长和脱落的循环
Across mammalian species, hairs have been modified for numerous purposes,
哺乳动物的毛质随用途而改变
ranging from the soft fluff covering rabbits
从兔子的柔软绒毛
to the rigid quills protecting porcupines.
到保护豪猪的坚硬刺
But for many mammals, hair grows in two layers
而许多哺乳动物的毛发分为两层
consisting of a shorter undercoat of ground hairs
包括内层较短的底毛
covered by longer guard hairs.
及外层较长的粗毛
Together, they help insulate the animal’s body and protect its skin.
它们一起帮助身体隔热并保护其皮肤
Human hairs, on the other hand, are kind of a combination of these hair types.
而人类的毛发则有点像是这些毛发类型的组合
Unfortunately, hair is rarely found in fossils,
不幸的是 在化石中很少发现毛发
making it hard for researchers to pinpoint when and how
这使得研究人员很难确定我们的祖先
our ancient ancestors lost their coats.
是何时以及怎样失去毛发外衣的
But scientists have developed some working hypotheses.
但是科学家们已经提出了一些可行的假设
It seems that, millions of years ago in Africa,
似乎 在数百万年前的非洲
early hominins first transitioned out of trees
早期人类离开森林后
and adopted a more active lifestyle.
适应了更活跃的生活方式
Keeping cool became increasingly important.
保持凉爽变得越来越重要
Eventually, they developed more sweat glands,
最终 他们进化出了更多的汗腺
which helped them lose heat by evaporating moisture through the skin.
这有助于他们通过皮肤蒸发出水分来散热
In fact, humans have 10 times more sweat glands than chimpanzees, for instance.
举个例子 事实上人类的汗腺是黑猩猩的10倍
But efficiently losing heat by sweating is harder to do when you’re covered in fur.
而当你全身都是毛发时 就很难通过出汗来有效地散热
Scientists believe that early humans lost much of their coat around this time
科学家们认为 早期人类大约就是在这个时期
to help their sweat evaporate faster.
失去了大部分的毛发 以便汗水快速蒸发
However, if losing our hair was so advantageous,
然而 既然脱毛如此有利
why do we have any left at all?
为什么还要留有毛发呢?
It seems that there are unique uses for hair in different parts of our bodies.
看起来我们身体不同部位的毛发都有其特殊的作用
When it comes to the tops of our heads,
当毛发长在我们的头顶时
temperature regulation likely played a part again.
温度调节可能再次发挥了作用
Since early humans began venturing into the open,
从早期人类在野外探险开始
their heads would’ve been exposed to the scorching sun.
他们的头部被暴露在烈日之下
Thicker, longer-growing hair protects our sensitive scalps
更浓 更长的头发保护着我们敏感的头皮
and keeps our brains from overheating.
防止我们的大脑过热
Dark tightly curled hair is most effective at keeping solar radiation off of skin.
深色 紧密且卷曲的头发最能有效地防止太阳辐射皮肤了
Other kinds of head hair evolved as humans moved to different places.
随着人类迁徙到不同的地方 人类也进化出其它种类的头发
Meanwhile, researchers think eyebrows are especially useful for communication
同时 研究人员认为眉毛在沟通交流中非常有用
because they sit atop active facial muscles that convey our feelings.
因为它们位于活跃的面部肌肉之上 用于传达情感
Eyelashes have been shown to minimize airflow over our eyeballs,
睫毛已被证明能减少眼球上方的气流
preventing them from drying out and catching debris.
防止眼球干燥 并减少灰尘进入
And maybe facial hair proved helpful in distinguishing identity from a distance,
也许面部毛发有助于远距离识别身份
but we really don’t know.
但这就不得而知了
Evidence is stubbly at best.
证据也只是零零碎碎的
Why we have hair in other regions is… more pungent.
为什么我们身体其他部位的毛发……气味更刺鼻呢?
Our armpits, nipples, and pubic areas are dotted with apocrine glands.
我们的腋窝 乳头和阴部布满了大汗腺
They produce oily, smelly secretions which the thick, curly hair
大汗腺会产生出油腻有臭味的分泌物
that often grows in these spots helps disperse.
而在这些部位生长的厚且卷的毛发能帮助散味
The secretions that waft up these hairy patches
从这些毛茸茸的部位上飘出来的分泌物气味
may be useful for identification.
可能有助于身份识别
For example, several studies have shown that people are able to identify
例如 多项研究表明 人们能够识别
their own armpit odors as well as those of people they’re close with.
自己的腋窝气味以及他们亲近的人的腋窝气味
The final type of notable human hair is the vellus hair that covers our bodies.
最后一类不得不提的人类毛发是覆盖在我们身体的毳毛
We don’t know if these hairs serve any purpose themselves,
我们不知道这些毛发本身是否有用
but the follicles vellus hair grows from are essential banks of stem cells
但长出毳毛的毛囊是干细胞重要的储藏地
that repair damaged skin after injury.
干细胞可以修复受伤后受损的皮肤
They’re also important sites of nerve endings that convey signals
它们也是神经末梢所在的重要部位
of gentle touch to the brain.
神经末梢可以向大脑传递轻触的信号
In fact, although it’s much finer,
事实上 虽然人类体毛的更细
humans have roughly the same density of body hair as apes of comparable sizes.
但是其密度与相同大小的猿类大致相同
So despite all this talk of human nakedness,
所以 尽管大家都在说人类赤裸无体毛
we’re not actually as hairless as we look.
但实际上我们并不像看上去的那么无毛
Here is far from the only evolutionary curiosity on the human body
而我们对人类身体进化的好奇远不止于此
Why do we still has tailbones and appendices
为什么我们还有尾椎骨和阑尾呢?
Check out to this video to learn about our evolutionary leftovers
点击我们的视频 了解人类进化的遗留问题
Or quick this video to learn how human are still evolving
或者快速观看这个视频了解为什么人类仍在进化

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视频概述

人类毛发进化史

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视频来源

https://www.youtube.com/watch?v=wd18yfQqa8A

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