Name: 当我们遇见其他人类时（When We Met Other Human Species）
Uploaded: 2021-05-02T05:50:31.000Z
Duration: 13 min 29 s
Description: 【看影片學英語】數萬部 YouTube 影片，搭配英漢字典即點即查，輕鬆掌握單字發音與用法，長久累積看電影不必再看字幕。

You and I belong to the only group of hominins on the planet today.

We're the lone twig left on our branch of the family tree.

100,000 years ago, Eurasia was home to other hominin species, some of which we know our

ancestors met, and spent some quality time with.

Some of them we've known about for a while, like the Neanderthals, whose fossils we've

But some of them are more recent additions to the family tree, like the Denisovans, who

who we may, on this channel, have called Denis-ovans but we have been informed

The Denisovans were discovered almost by accident in 2008, and we know them from only a few fossil bones

and from the DNA of their living descendants.

That surprising discovery has opened our eyes to the fact that our ancestors met, and even

So now, anthropologists are following the genetic traces of these ancient interbreeding

events -- traces that many of us carry with us today.

Thanks to this research, we're starting to better understand how and even where modern

humans paired up with other hominins, giving us a more complete picture of the history

And we're starting to tackle some really exciting questions, like: What's our inheritance

from that time when we met up with other human species?

As we get closer to answering those questions, we're starting to see that maybe part of

our success as a species has to do with those other hominins that we encountered in our

Neanderthals lived throughout Europe, and from southwestern to central Asia.

We've found their fossils from Portugal and the UK in the west all the way to the

Altai Mountains of Siberia in the east, and down into Israel in the south.

The oldest Neanderthal-like fossils come from a site in northern Spain called the “Sima

de los Huesos” - literally, the Pit of the Bones - dated to about 450,000 years ago,

while the most recent come from a handful of sites across western Europe that date to

Anatomically, the Neanderthals were very much like us, with a few differences.

They were relatively short and stocky, with robust limbs, and big brains.

They had heavy brow ridges, large noses, and braincases with more of an oval shape than

And we know they weren't just dumb cavemen.

They controlled fire, created stone tools and spears, made jewelry from eagle talons,

and cared for injured members of their groups.

And our ancestors clearly recognized them as being like us -- enough so that we interbred

We know this because researchers have sequenced the Neanderthal nuclear genome, originally

in 2010, from bone fragments found in a cave in Croatia.

And by comparing that genome to those of modern humans from many different populations, we

can find out how much Neanderthal DNA some of us still carry.

Although original estimates were around 4%, more recent studies have suggested that living

people of European and East Asian descent have between 1 to 2% Neanderthal DNA in their

Meanwhile, people native to Sub-Saharan Africa don't have any Neanderthal DNA, indicating

that their ancestors never encountered Neanderthals.

And as we find more fossils to sample, we can tell that these interbreeding encounters

And our genomes can even shed light on when they happened.

For example, genetic material extracted from the left femur of a modern human male who

lived in Siberia about 45,000 years ago has been found to contain Neanderthal DNA.

And researchers were able to measure how long the Neanderthal segments of his genome were,

compared to the same segments in living people.

It turned out that his Neanderthal sections were longer than modern humans', suggesting

that he wasn't that many generations removed from his Neanderthal ancestor.

In fact, the researchers were able to estimate that this Siberian man was the product of

an interbreeding event between Neanderthals and Homo sapiens that occurred 50,000 to 60,000

years ago -- just 10,000 years before he was born, give or take a few thousand years.

And this was likely when modern humans migrating out of Africa encountered Neanderthals in

Likewise, a 40,000-year-old jawbone was found in Romania in 2002, which provided some of

the earliest evidence of modern humans in Europe.

And it was found to have some anatomical similarities to Neanderthals.

When its genome was sequenced over a decade later, that human was found to have had a

Neanderthal ancestor only some four to six generations back.

Between 6 and 9% of its genome was Neanderthal!

So, using fossils like these, researchers have been able to determine that Homo sapiens

bred with Neanderthals several times in different places.

But how did all of this interbreeding change us?

The genome from the Romanian jaw bone suggested that population didn't contribute much to

But sometimes, these encounters had a big impact.

For example, two genes that play important roles in our immune response seem to have

passed from Neanderthals to people of Eurasian descent.

One of these genes, known as STAT2, is part of our immune system's signaling response

And we know that the Eurasian version of STAT2 came from Neanderthals, because it isn't

Plus, molecular-clock studies have found that the Neanderthal version of this gene appeared

in the Eurasian genome long after the evolutionary split between Homo sapiens and Neanderthals

Meanwhile, members of many East Asian populations have been found to carry a gene known as HYAL2,

which is involved in skin-cell repair after skin has been exposed to the sun's UVB rays

And this gene also seems to have come from the Neanderthals, likely a helpful adaptation

These genes are both examples of a phenomenon known as adaptive introgression, when genetic

material from one species moves into the gene pool of another species, and then is selected

But these genetic contributions also can have a downside.

Introgressed genes that were once beneficial can become less-so over time, as the environment

in which natural selection is taking place changes.

For example, there's a gene that's involved in the rapid coagulation of blood, which used

to be really beneficial before medical care was available.

But now that gene has been found to increase the risk of blood clots.

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当我们遇见其他人类时（When We Met Other Human Species）

intense

immune

material

evidence