Is human evolution speeding up or slowing down? - Laurence Hurst

譯者: Hilda Chan 審譯者: Yi-Ping Cho (Marssi)

The Tibetan high plateau lies about 4500 meters above sea level,

西藏高原位於海拔四千五百米，

with only 60% of the oxygen found below.

氧氣濃度只有平地的百分之六十。

While visitors and recent settlers struggle with altitude sickness,

正當遊客或新來的居民 因高原反應而苦苦掙扎時，

native Tibetans sprint up mountains.

土生土長的西藏人 卻可輕鬆地在山間跑動。

This ability comes not from training or practice,

這種能力不是來自訓練，

but from changes to a few genes that allow their bodies

而是來自某幾個基因的變異，

to make the most of limited oxygen.

讓他們的身體得以 將有限的氧氣物盡其用。

These differences are apparent from birth—

從出生起，這些分別便很明顯──

Tibetan babies have, on average, higher birth weights,

平均來說，西藏寶寶出生時較重、

higher oxygen saturation,

有較高的血氧飽和度，

and are much likelier to survive than other babies born in this environment.

比其他在相同環境出生的寶寶 更有可能生存下來。

These genetic changes are estimated to have evolved

這些基因變異估計 在過去約三千年演化而來，

over the last 3,000 years or so, and are ongoing.

而且還在持續地發生。

That may sound like a long time,

這聽起來是一段長時間，

but would be the fastest an adaptation has ever evolved in a human population.

但已是人類群體中 最快演化出來的適應。

It’s clear that human evolution isn’t over—

顯然人類的演化還未完結──

so what are other recent changes?

那麼還有哪些近期發生的變異？

And will our technological and scientific innovations impact our evolution?

而我們的各種科技創新 會影響我們的演化嗎？

In the past few thousand years,

過去的幾千年裏，

many populations have evolved genetic adaptations to their local environments.

許多群體演化出各種基因適應， 以應付他們周遭的環境。

People in Siberia and the high arctic are uniquely adapted to survive extreme cold.

在西伯利亞和北極生活的人 特別適應極冷的天氣。

They’re slower to develop frostbite,

他們比較慢長出凍瘡，

and can continue to use their hands in subzero temperatures

他們的雙手也可在零下的温度裏，

比大部分人活動更久。

much longer than most people.

They’ve undergone selection for a higher metabolic rate

他們經歷過天擇，

that increases heat production.

有較快的新陳代謝 能製造更多體熱。

Further south, the Bajau people of southeast Asia can dive 70 meters

在南方，東南亞的 巴瑤族人可下潛七十米，

and stay underwater for almost fifteen minutes.

並在水底逗留近十五分鐘。

Over thousands of years living as nomadic hunters at sea,

數千年以來，巴瑤族 生活得像海中的遊牧獵人，

they have genetically-hardwired unusually large spleens that act as oxygen stores,

他們的基因 使他們的胰臟大得不尋常，

可用作氧氣存庫， 讓他們得以留在水底更久──

enabling them to stay underwater for longer—

an adaptation similar to that of deep diving seals.

類似可深潛的海豹所作的適應。

Though it may seem pedestrian by comparison,

相比起來，喝奶的能力 雖然看似平平無奇，

the ability to drink milk is another such adaptation.

這卻是一項類似的適應策略。

All mammals can drink their mother’s milk as babies.

所有哺乳類動物 在嬰兒時期都能喝母乳。

After weaning they switch off the gene that allows them to digest milk.

斷奶後，牠們會關掉 容許牠們消化奶汁的基因。

But communities in sub-Saharan Africa, the middle east and northwest Europe

但是在非洲撒哈拉以南地區、 中東和歐洲西北地區

that used cows for milk have seen a rapid increase in DNA variants

飲用牛奶的社群中，

過去七至八千年間的 DNA 變體 大大增加，以防止那個基因關掉。

that prevent the gene from switching off over the last 7 to 8000 years.

At least in Europe, milk drinking may have given people a source of calcium

至少在歐洲，飲用牛奶 或為人們提供了鈣的來源，

to aid in vitamin D production, as they moved north and sunlight,

幫助身體製造維他命 D， 特別是當人們向北方遷移時，

the usual source of vitamin D, decreased.

作為一般維他命 D 來源的日照減少了。

Though not always in obvious ways,

雖然這些變異並不一定都很明顯，

all of these changes improve people’s chance of surviving to reproductive age—

但全部變異都讓人有更大機會 存活至可生育的年紀──

that’s what drives natural selection,

這正正驅使天擇發生，

the force behind all these evolutionary changes.

而天擇就是所有演化背後的推動力。

Modern medicine removes many of these selective pressures

現代醫學去除許多類似的篩選壓力，

by keeping us alive when our genes,

讓我們得以保命，

即使有時候我們的基因 和傳染病聯手的情況下

sometimes combined with infectious diseases,

would have killed us.

本來會把我們殺死。

Antibiotics, vaccines, clean water and good sanitation

抗生素、疫苗、 乾淨的飲用水和良好的衛生，

all make differences between our genes less important.

全都使我們的基因差別不那麼重要。

Similarly, our ability to cure childhood cancers,

同樣地，我們能夠治癒兒童癌症、

surgically extract inflamed appendixes, and deliver babies

以手術切除發炎的闌尾，

及讓因特殊分娩狀況 而命危的媽媽順利生產，

whose mothers have life-threatening pregnancy-specific conditions,

all tend to stop selection by allowing more people to survive

這些都是在透過讓更多人 存活至可生育的年紀來阻擋天擇。

to a reproductive age.

But even if every person on Earth has access to modern medicine,

但即使地球上每一個人 都能接受現代醫學治療，

it won’t spell the end of human evolution.

也不意味人類的演化會結束。

That’s because there are other aspects of evolution besides natural selection.

因為除了天擇， 演化還有其他不同的方面。

Modern medicine makes genetic variation

現代醫學讓原本 取決於天擇的基因差異

that would have been subject to natural selection

subject to what’s called genetic drift instead.

轉而取決於「基因漂變」。

With genetic drift, genetic differences vary randomly within a population.

受到基因漂變影響，

一個群體內的基因會有隨機的差異。

On a genetic level, modern medicine might actually increase variety,

在基因的層面， 現代醫學或許促進了多樣性，

because harmful mutations don’t kill people and thus aren’t eliminated.

因為有害的突變不再將人殺死， 也因而沒有被淘汰。

This variation doesn’t necessarily translate to observable, or phenotypic,

不過，這種差異不一定 以可見或可表現的形式

differences among people, however.

呈現在人們身上。

Researchers have also been investigating whether genetic adaptations

研究者也在調查

究竟基因會否透過表觀遺傳修飾

to a specific environment could appear very quickly

而很快地出現對特定環境的調適。

through epigenetic modification: changes not to genes themselves,

即變異不在基因本身，

but to whether and when certain genes are expressed.

而在於某些基因 會否和何時被表現出來，

These changes can happen during a lifetime,

這些改變可以在一生之中發生，

and may even be passed to offspring—

甚至可能傳給後代──

but so far researchers are conflicted over whether epigenetic modifications

但目前研究人員還在爭論

到底表觀遺傳修飾 能否跨越世代保留下來，

can really persist over many generations

and lead to lasting changes in populations.

然後在群體中造成永久的轉變。

There may also be other contributors to human evolution.

或許還有其他東西促使人類演化。

Modern medicine and technology are very new,

現代醫學和科技 也只出現了很短時間，

even compared to the quickest, most recent changes by natural selection—

即使是跟最快速最近期 因天擇出現的變異比較──

so only time can tell how our present will shape our future.

所以我們只能等待， 才會知道我們的現在怎樣塑造未來。