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

翻译人员: Yuyang Liu 校对人员: Cissy Yun

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

在海拔4500米高的青藏高原上，

with only 60% of the oxygen found below.

氧气含量只有平原上的60%。

While visitors and recent settlers struggle with altitude sickness,

当游客和新定居者 饱受高原反应困扰时，

native Tibetans sprint up mountains.

西藏人却可以轻松地爬上山。

This ability comes not from training or practice,

这不是通过训练或练习得来的，

but from changes to a few genes that allow their bodies

而是因为某些基因的不同，

让身体可以充分利用有限的氧气。

to make the most of limited oxygen.

These differences are apparent from birth—

这些变化从出生就开始了——

Tibetan babies have, on average, higher birth weights,

有当地血统的婴儿 平均有更长的身长，

higher oxygen saturation,

更高的血氧饱和度，

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

比当地出生的其他婴儿更易存活。

These genetic changes are estimated to have evolved

这些遗传性变化估计 从三千年前开始，

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

并且仍在进化。

That may sound like a long time,

三千年听起来很长，

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

但在人类所有适应进化中是最快的。

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

人类的进化从未停止——

so what are other recent changes?

那么最近有哪些变化呢？

And will our technological and scientific innovations impact our evolution?

科技发展会影响人类进化的过程吗？

In the past few thousand years,

在过去几千年中，

many populations have evolved genetic adaptations to their local environments.

很多人类族群进化出了 适应当地环境的基因。

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

比如西伯利亚人和北极人 可以在极端寒冷中生活。

They’re slower to develop frostbite,

他们比常人更难长冻疮，

and can continue to use their hands in subzero temperatures

同时在零下温度中，

much longer than most people.

可以用手劳作更长的时间。

They’ve undergone selection for a higher metabolic rate

他们有更高的新陈代谢率，

that increases heat production.

产生更多热量来挺过自然选择的考验。

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

而在南边，东南亚的巴茹人 可以潜入70米水深，

and stay underwater for almost fifteen minutes.

并在水里停留15分钟。

Over thousands of years living as nomadic hunters at sea,

作为在海上生活几千年的“游牧民族”，

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

他们拥有与生俱来的 更大的脾，可以存储氧气，

enabling them to stay underwater for longer—

帮助他们在水下停留更长时间——

an adaptation similar to that of deep diving seals.

就像海豹的遗传适应一样。

Though it may seem pedestrian by comparison,

虽然和前面比起来较平凡，

the ability to drink milk is another such adaptation.

但饮奶也是另一种适应。

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

所有哺乳动物在婴儿时期都喝母乳。

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

断奶后他们会关闭消化奶类的基因。

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

在撒哈拉沙漠以南非洲、 中东和欧洲西北部，

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

养牛饮奶的族群中， 出现DNA变体的激增，

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

在过去七、八千年里 阻止了消化奶类基因的关闭。

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

在欧洲，人们需要饮奶吸收钙元素，

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

来帮助人体制造维生素D。 因为当他们往北迁徙时，

提供维生素D的阳光会逐渐减少。

the usual source of vitamin D, decreased.

Though not always in obvious ways,

虽然不总是以明显的方式，

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

这些变化都提高了 人们达到生育年龄前的存活率——

that’s what drives natural selection,

这驱动着自然选择，

the force behind all these evolutionary changes.

在背后推动所有进化的力量。

Modern medicine removes many of these selective pressures

现代医学解决了 很多类似的选择压力，

by keeping us alive when our genes,

比如说，

在我们的基因遇到致命传染病时，

sometimes combined with infectious diseases,

would have killed us.

保护了我们的生命。

Antibiotics, vaccines, clean water and good sanitation

抗生素、疫苗、净水 以及良好的卫生环境，

all make differences between our genes less important.

都让我们基因上的不同 变得没那么重要。

Similarly, our ability to cure childhood cancers,

在相同情况下， 可以治疗儿童癌症、

surgically extract inflamed appendixes, and deliver babies

做阑尾炎手术、

whose mothers have life-threatening pregnancy-specific conditions,

在孕妇有生命危险时成功接生，

all tend to stop selection by allowing more people to survive

都阻止了自然选择， 让更多人活下来，

to a reproductive age.

直到健康成长到生育年龄。

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

但即使地球上每个人 都能得到现代医学的治疗，

it won’t spell the end of human evolution.

人类的进化也不会由此终止。

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

因为除了自然选择， 依然有其他进化的因素。

Modern medicine makes genetic variation

现代医学让遗传变异，

that would have been subject to natural selection

从原本的服从自然选择，

subject to what’s called genetic drift instead.

变为服从遗传漂移。

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

遗传漂移让族群里的基因差异随机变化。

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

从遗传学角度来说， 现代医学会让基因多样性增加，

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

因为有害的基因突变 不再致死并被延续下来。

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

不过，这些变异不一定会造成 能被观察到的、表型的差异。

differences among people, however.

Researchers have also been investigating whether genetic adaptations

研究者们也正在探究

在特定环境下快速产生的遗传适应

to a specific environment could appear very quickly

是否与表观遗传修饰有关：

through epigenetic modification: changes not to genes themselves,

不是因为基因本身变化，

but to whether and when certain genes are expressed.

而是根据一些基因 是否或何时会被表达。

These changes can happen during a lifetime,

遗传适应的变化是终生的，

and may even be passed to offspring—

甚至可能传给后代。

but so far researchers are conflicted over whether epigenetic modifications

但到目前为止，研究者 仍在争论表观遗传修饰造成的变化

can really persist over many generations

是否可以传给多代后代，

and lead to lasting changes in populations.

对族群造成长久的影响。

There may also be other contributors to human evolution.

此外可能也有其他因素 影响着人类的进化。

Modern medicine and technology are very new,

即使与自然选择所带来的 最新最快的变化相比，

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

现代医学技术发展时长较短——

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

只有时间能告诉我们 现在会如何影响未来。