The science of skin color - Angela Koine Flynn

翻译人员: Yi Li 校对人员: Leo Wei

When ultraviolet sunlight hits our skin,

当紫外线照射到皮肤上时，

它对我们的影响因人而异。

it affects each of us a little differently.

Depending on skin color, it will take only minutes of exposure

取决于肤色， 一个人只在阳光下暴露几分钟，

to turn one person beetroot-pink,

就会晒成甜菜根般的红色，

while another requires hours to experience the slightest change.

而另一个人，需要几小时的暴露，

才能体现轻微的肤色改变。

So what's to account for that difference

到底怎样解释这种差异呢？

and how did our skin come to take on so many different hues to begin with?

我们的皮肤又是怎样

呈现出如此多不同的肤色呢？

Whatever the color,

无论怎样的肤色，

our skin tells an epic tale of human intrepidness and adaptability,

我们的皮肤都在讲述一段人类

无惧和适应性的史诗般的故事。

revealing its variance to be a function of biology.

肤色的多变性是一项生物学功能，

It all centers around melanin,

这一切都围绕着黑色素，

the pigment that gives skin and hair its color.

这种颜料赋予皮肤和头发的颜色。

This ingredient comes from skin cells called melanocytes

这种成分来源于被称为 黑素细胞的皮肤细胞。

and takes two basic forms.

它具有两种形式。

There's eumelanin, which gives rise to a range of brown skin tones,

其中一种叫真黑色素,

它产生一系列的褐色皮肤，

as well as black, brown, and blond hair,

以及黑色，棕色以及金色的头发。

and pheomelanin, which causes the reddish browns of freckles and red hair.

另一种是伪黑色素， 则生成褐色雀斑和红色头发。

But humans weren't always like this.

但人类并不总是这样，

Our varying skin tones were formed by an evolutionary process

我们不同色调的皮肤是

受太阳驱动的进化过程中形成的。

driven by the Sun.

In began some 50,000 years ago when our ancestors migrated north from Africa

它大约起源于五万年前， 当我们的祖先从非洲北上，

and into Europe and Asia.

迁移到欧洲与亚洲时。

These ancient humans lived between the Equator and the Tropic of Capricorn,

这些远古人类生活在赤道 和南回归线之间，

a region saturated by the Sun's UV-carrying rays.

这部分地域充满了紫外线。

When skin is exposed to UV for long periods of time,

当皮肤被长期暴露于紫外线中，

the UV light damages the DNA within our cells,

紫外线会损坏细胞中的基因， 皮肤开始烧伤。

and skin starts to burn.

If that damage is severe enough,

如果损伤足够严重,

细胞突变可导致黑素瘤，

the cells mutations can lead to melanoma,

a deadly cancer that forms in the skin's melanocytes.

这是一种由皮肤中的黑色素细胞形成的致命癌症。

Sunscreen as we know it today didn't exist 50,000 years ago.

我们今天所知的防晒霜， 在五万年前并不存在。

So how did our ancestors cope with this onslaught of UV?

那么我们的祖先是如何

应对大量的紫外线照射的呢？

The key to survival lay in their own personal sunscreen

生存的关键在于他们自身的防晒霜，

manufactured beneath the skin: melanin.

也就是皮下产生的黑色素。

The type and amount of melanin in your skin

你们皮肤中黑色素的种类和数量，

determines whether you'll be more or less protected from the sun.

决定了你在受太阳照射时， 是多，还是少的受保护程度。

This comes down to the skin's response as sunlight strikes it.

这取决于阳光照射时皮肤的反应。

When it's exposed to UV light,

当暴露在紫外线下时，

that triggers special light-sensitive receptors called rhodopsin,

将触发被称为紫膜质的特殊感光受体。

which stimulate the production of melanin to shield cells from damage.

它促进黑色素的产生， 以保护细胞免受损伤。

For light-skin people, that extra melanin darkens their skin and produces a tan.

对于肤色偏浅的人来说, 额外的黑色素 会使肤色加深变为黄褐色。

Over the course of generations,

经历无数代后，

humans living at the Sun-saturated latitudes in Africa

生活在非洲阳光饱和的纬度的人们

adapted to have a higher melanin production threshold

已经进化到拥有更高的 黑色素的生产阈值

and more eumelanin,

和更多真黑素，

giving skin a darker tone.

使皮肤拥有更深的色调。

This built-in sun shield helped protect them from melanoma,

这种自身的防太阳光紫外线保护层 可防止黑素瘤的形成，

likely making them evolutionarily fitter

他们为适应环境而进化，

and capable of passing this useful trait on to new generations.

并且将这种特性代代相传。

But soon, some of our Sun-adapted ancestors migrated northward

但是不久，部分适应日晒的 祖先们离开了热带区域，

out of the tropical zone,

往北上移居，

spreading far and wide across the Earth.

他们广泛的迁移到世界各地。

The further north they traveled, the less direct sunshine they saw.

他们越往北，看见到的阳光就越少。

This was a problem because although UV light can damage skin,

这有一个问题，

因为尽管紫外线会损伤皮肤，

it also has an important parallel benefit.

同时它对人体有一个重要的益处。

UV helps our bodies produce vitamin D,

紫外线帮助身体产生维素D，

an ingredient that strengthens bones and lets us absorb vital minerals,

这种物质可以强化骨骼， 并帮助我们吸收重要的矿物质，

like calcium, iron, magnesium, phosphate, and zinc.

比如钙，铁，镁，磷酸盐，锌。

Without it, humans experience serious fatigue and weakened bones

没有它，人体会感到极为疲乏且骨骼脆弱，

that can cause a condition known as rickets.

这种状况被称为佝偻病。

For humans whose dark skin effectively blocked whatever sunlight there was,

对于那些深色皮肤有效地阻止了任何阳光的人，

vitamin D deficiency would have posed a serious threat in the north.

在北方维生素D缺乏将造成严重威胁。

But some of them happened to produce less melanin.

但是他们中的一些人正好产生较少黑色素。

They were exposed to small enough amounts of light that melanoma was less likely,

他们暴露在少量的阳光下， 是不大可能产生黑色素瘤的，

and their lighter skin better absorbed the UV light.

并且他们的浅色皮肤能更好地吸收紫外线。

So they benefited from vitamin D,

因此他们得益于维生素D，

developed strong bones,

发育出强健的骨骼，

and survived well enough to produce healthy offspring.

并能更好的生存，繁衍健康的后代。

Over many generations of selection,

经过很多代的自然选择后，

skin color in those regions gradually lightened.

居住在那些区域的人的肤色逐渐淡化。

As a result of our ancestor's adaptability,

作为我们祖先适应的结果，

today the planet is full of people with a vast palette of skin colors,

如今我们的地球上充满了各种肤色的人，

typically, darker eumelanin-rich skin in the hot, sunny band around the Equator,

通常，黑色素丰富的深色皮肤的人 生活在炎热的，阳光充足的赤道带；

and increasingly lighter pheomelanin-rich skin shades fanning outwards

从赤道呈扇形越往外阳光越少， 含有伪黑色素的皮肤的人

as the sunshine dwindles.

肤色也越来越浅。

Therefore, skin color is little more than an adaptive trait for living on a rock

因此，肤色仅仅是 生活在围绕太阳运行的

地球上的人们的适应特征。

that orbits the Sun.

It may absorb light,

它可以吸收阳光，

but it certainly does not reflect character.

但肯定不反应品格。