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  • When ultraviolet sunlight hits our skin, it affects each of us a little differently.


  • Depending on skin color, it will take only minutes of exposure to turn one person beetroot-pink, while another requires hours to experience the slightest change.

    根據皮膚的顏色, 有的人只要曝曬幾分鐘,皮膚就變得像甜菜根一樣紅,而有的卻需要數小時才有絲毫的改變。

  • So what's to account for that difference?


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


  • Whatever the color, our skin tells an epic tale of human intrepidness and adaptability, revealing its variance to be a function of biology.


  • It all centers around melanin, the pigment that gives skin and hair its color.


  • This ingredient comes from skin cells called melanocytes and takes two basic forms.

    這種要素來自皮膚細胞 ─ 稱為「黑素細胞」,黑色素有兩種基本型。

  • There's eumelanin, which gives rise to a range of brown skin tones, as well as black, brown, and blond hair, and pheomelanin, which causes the reddish browns of freckles and red hair.


  • But humans weren't always like this.


  • Our varying skin tones were formed by an evolutionary process driven by the Sun.


  • In began some 50,000 years ago when our ancestors migrated north from Africa and into Europe and Asia.

    5 萬多年前開始, 我們的祖先從非洲往北遷移到歐洲和亞洲。

  • These ancient humans lived between the Equator and the Tropic of Capricorn, a region saturated by the Sun's UV-carrying rays.


  • When skin is exposed to UV for long periods of time, the UV light damages the DNA within our cells, and skin starts to burn.

    當皮膚長時間暴露於紫外線下,紫外線會損害我們的細胞內的 DNA,皮膚開始曬傷。

  • If that damage is severe enough, the cells mutations can lead to melanoma, a deadly cancer that forms in the skin's melanocytes.


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

    現今我們所知道的防曬霜 在5 萬年前並不存在。

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


  • The key to survival lay in their own personal sunscreen manufactured beneath the skin: melanin.


  • The type and amount of melanin in your skin determines whether you'll be more or less protected from the sun.


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


  • When it's exposed to UV light, that triggers special light-sensitive receptors called rhodopsin, which stimulate the production of melanin to shield cells from damage.

    當皮膚暴露於紫外線下,會觸發特殊的感光受體 ─ 稱為「視紫質」,它會刺激黑色素的產生, 以免細胞遭受破壞。

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


  • Over the course of generations, humans living at the Sun-saturated latitudes in Africa adapted to have a higher melanin production threshold and more eumelanin, giving skin a darker tone.


  • This built-in sun shield helped protect them from melanoma, likely making them evolutionarily fitter and capable of passing this useful trait on to new generations.


  • But soon, some of our Sun-adapted ancestors migrated northward out of the tropical zone, spreading far and wide across the Earth.


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

    他們越往北移動, 就越少見到陽光的直射。

  • This was a problem because although UV light can damage skin, it also has an important parallel benefit.

    這是一個問題, 因為雖然紫外線會損傷皮膚,但它同時也有重要的好處。

  • UV helps our bodies produce vitamin D, an ingredient that strengthens bones and lets us absorb vital minerals, like calcium, iron, magnesium, phosphate, and zinc.

    紫外線可幫助我們身體產生維生素D ─ 一種強化骨骼並讓我們吸收重要礦物質的成分如鈣、鐵、鎂、磷酸鹽和鋅。

  • Without it, humans experience serious fatigue and weakened bones that can cause a condition known as rickets.

    沒有它,人類會感到嚴重疲勞且骨骼脆弱,這會造成一種疾病, 稱為「佝僂病 (軟骨病)」。

  • For humans whose dark skin effectively blocked whatever sunlight there was, vitamin D deficiency would have posed a serious threat in the north.


  • But some of them happened to produce less melanin.

    但他們之中有些人, 恰好產生較少的黑色素。

  • They were exposed to small enough amounts of light that melanoma was less likely, and their lighter skin better absorbed the UV light.

    由於他們暴露在量夠少的陽光下, 所以罹患黑色素瘤的可能性較小,且他們皮膚較白,更容易吸收紫外線。

  • So they benefited from vitamin D, developed strong bones, and survived well enough to produce healthy offspring.

    於是,他們從維生素 D 中受益,形成強健骨骼,而且存活良好, 足以繁育健康的後代。

  • Over many generations of selection, skin color in those regions gradually lightened.


  • As a result of our ancestor's adaptability, today the planet is full of people with a vast palette of skin colors, typically, darker eumelanin-rich skin in the hot, sunny band around the Equator, and increasingly lighter pheomelanin-rich skin shades fanning outwards as the sunshine dwindles.


  • Therefore, skin color is little more than an adaptive trait for living on a rock that orbits the Sun.


  • It may absorb light, but it certainly does not reflect character.


When ultraviolet sunlight hits our skin, it affects each of us a little differently.



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B2 中高級 中文 TED-Ed 皮膚 紫外線 黑色素 膚色 陽光

【TED-Ed】膚色的科學--安吉拉-科因-弗林 (【TED-Ed】The science of skin color - Angela Koine Flynn)

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    Sh, Gang (Aaron) 發佈於 2021 年 01 月 14 日