Home
登录
注册
学习内容
Loading...
听力练习
听力练习
/
Video
/
SciShow
/
Where Are Humans ACTUALLY From?
Where Are Humans ACTUALLY From?
选择学习模式:
查看字幕
选词
重写单词
Highlight:
3000 Oxford Words
4000 IELTS Words
5000 Oxford Words
3000 Common Words
1000 TOEIC Words
5000 TOEFL Words
字幕 (278)
0:00
Have you ever wondered where we humans got our start?
0:02
I mean, it’s Africa.
0:04
We know that.
0:05
But Africa is a big place.
0:07
So the follow up question is,
0:09
where specifically in Africa did we come from?
0:12
What seems like a simple question isn’t.
0:15
There are multiple theories and a lot of evidence pointing in different directions.
0:19
But there’s a group of people living in Southern Africa today
0:23
who are the most genetically diverse population on the planet.
0:26
And a clue about our origins may be hidden in their genes.
0:31
[intro music]
0:35
Before we get too far along,
0:36
I’ll clarify that we’re going to be specifically focusing
0:38
on the origin story of our human species, Homo sapiens.
0:43
A number of close relatives of ours that collectively
0:46
made up an archaic human group, all in our same genus.
0:50
With all those other archaic humans wandering about,
0:52
it can be tricky to not only figure out
0:55
when we branched off from our last common ancestor,
0:58
but more specifically when we truly became us,
1:01
both anatomically and behaviorally.
1:04
But at least we know generally where to start.
1:06
Because when we’re talking about the origin of humans,
1:09
there’s no doubt that we come from Africa.
1:12
From fossil and material remains to full genomes
1:14
sequenced from today’s human populations
1:16
and as well as from early human remains,
1:19
our African origin is crystal clear.
1:22
Not that it was always the most popular idea with everyone,
1:25
but we don’t have time for all that.
1:27
But even after everyone finally agreed that our species came from Africa,
1:31
there was still debate around how much of our species really started there.
1:36
Basically, it was a battle of the hypotheses,
1:39
with two very different ideas about what the origination of our species looked like.
1:44
One of these was the multiregional hypothesis,
1:46
championed for decades by Milford Wolpoff.
1:49
This hypothesis emerged in the 1980s and was tweaked in the early 2000s,
1:54
but the overall vibe stayed the same.
1:57
The idea is that although our ancestral history began in Africa,
2:01
our modern species didn’t rise from a single place, but spread across continents.
2:07
Basically, the species that we came from left Africa before it was… us.
2:12
Then they got to all these cool new places
2:13
but kept in touch with their relatives across the world,
2:16
enough that all those populations still could be considered one species.
2:21
But because they were so far apart,
2:23
each of those populations evolved really different traits,
2:26
which basically explains how these so-called
2:29
“identifiable geographic differences” could show up.
2:32
If you think this sounds like a roundabout way
2:34
of trying to validate preconceptions of human races….
2:38
Well, you might be onto something there.
2:40
And while Wolpoff and his supporters
2:42
have stuck by this hypothesis for the long haul,
2:45
the much more widely accepted explanation of modern human origins
2:49
is the Out of Africa theory.
2:51
Out of Africa proposes that our ancestors
2:53
who migrated around the world were already full fledged modern Homo sapiens,
2:59
no regional evolutionary stuff needed.
3:01
And the evidence for this version of events is pretty strong.
3:05
For one, we have the fossils.
3:06
The oldest Homo sapiens fossils all come from Africa,
3:10
and it’s not even close.
3:12
The earliest Homo sapiens fossils found in Africa,
3:14
which combine modern and archaic features, a
3:17
re around 315 thousand years old.
3:20
Meanwhile, the oldest one from outside of Africa,
3:23
found in southeast Europe,
3:25
was closer to 210,000 years old, so no contest there.
3:29
And as best we can tell, the population of our ancestors
3:32
where that European fossil came from was a dead end.
3:36
If this was a multi-region situation,
3:39
you’d expect there to have been people living in that area
3:42
after the time that fossil was found, and that isn’t the case here.
3:44
Even though modern Homo sapiens first appeared in Africa
3:46
more than 300,000 years ago,
3:49
it took hundreds of thousands of years for any human populations
3:52
to really get going anywhere else outside of the continent.
3:55
Which means that any direct, fossil based arguments
3:58
for multi-regional origins are just not well supported.
4:02
But what really sealed the deal on Out of Africa
4:05
was the rise of DNA analysis,
4:08
because we could use that DNA evidence
4:09
to look for patterns in the genetic variation between populations.
4:13
Every time a population splits up,
4:15
that departing population goes through what’s called the founder effect.
4:19
Basically, this smaller fragment of the original population
4:23
can only bring so much genetic material with them
4:26
from their original gene pool,
4:28
so the migrant group won’t be as genetically diverse
4:31
as the group they came from was .
4:33
From there, that group might split off again
4:35
as they continue to move into new regions,
4:37
and their gene pool narrows once again.
4:40
So if some of our ancestors were to do something like,
4:43
oh I don't know,
4:44
leave their area of origin in a mass migration event,
4:47
we can just follow the genetic trail backward
4:50
from least to most variation to find where that original home was.
4:54
A great place to start looking for that genetic evidence is our mitochondria.
4:59
They are, of course, the powerhouse of the cell,
5:01
but they also have their own DNA inside them,
5:04
which is different from the chromosomes we have in our cell nuclei.
5:08
And we only inherit our mitochondrial DNA from our mothers,
5:12
regardless of whether the offspring are male or female.
5:15
This makes mitochondrial DNA very handy
5:17
for tracking genetic inheritance patterns across populations.
5:21
You do this by looking at the genetic haplogroups;
5:24
clusters of tightly linked genes inherited together from a particular location on DNA.
5:30
Mapping out the haplogroups
5:31
looks like any other evolutionary tree,
5:34
because that’s basically what it is.
5:36
And if you follow it all the way back,
5:38
you can find the very earliest groups
5:40
that gave rise to all the rest of them further down the tree.
5:44
Those giant groups are called macrogroups.
5:47
The oldest macrogroup humans have is macrogroup L,
5:51
which has eight lineages, L0 to L7,
5:55
You can find people living in Africa today
5:57
whose mitochondria come from any of those lineages.
6:00
So if you can trace your ancestry back to Africa directly,
6:04
you could have DNA from any haplogroup.
6:07
But for the non-African folks, it’s another story.
6:10
All the other historic and prehistoric populations of humans outside Africa
6:15
can trace their mitochondrial DNA to just one group, L3.
6:20
Scientists believe people with that L3 haplogroup
6:23
migrated into Europe and Asia 55 to 85 thousand years ago.
6:28
And as far as we can tell,
6:30
all the haplogroups found in people indigenous to places outside Africa
6:34
branched off from that single group.
6:37
And to be clear, there’s been plenty of mixture of populations
6:40
in and out of Africa since then,
6:42
so we’re talking about the oldest established groups of people
6:45
to hang out outside Africa full-time. If the multiregional hypothesis were true,
6:51
we would expect a lot of deep lineages of mitochondrial DNA,
6:55
since all the populations around the world
6:57
would have been interbreeding for so long that all the diversity got spread around.
7:02
Instead, we have one of the most striking
7:04
and conclusive examples of the founder effect, right inside our cells.
7:08
Thanks to mitochondrial DNA,
7:10
we’re now confident that we first became the modern human species
7:13
we are today while still living in Africa,
7:16
even if we picked up a little extra DNA here and there.
7:20
But all this still left us pondering where specifically in Africa
7:23
did our species first arrive on the scene.
7:26
Africa is a huge continent after all.
7:29
So how can we figure out where our species got its start?
7:32
Well, we can start narrowing down our options by looking at the places
7:36
where we find the oldest modern human fossils.
7:39
And while that’s a good starting point,
7:40
that probably won’t be the way we get our answer on its own.
7:44
For one, we can’t guarantee we’ve even found
7:46
the oldest modern human fossils yet,
7:48
because they tend to be buried underground and hard to find.
7:52
Another tricky consideration is that there could be a significant span of time
7:56
between when our bodies were anatomically modern humans,
8:00
and when our brains were.
8:02
It’s pretty tough to know when our behavior and problem-solving skills
8:05
first appeared in a way that aligns with our current capabilities.
8:09
Clearly, narrowing down our species’ original home base is no easy task,
8:13
so we once again turn to DNA for help.
8:16
While mitochondrial DNA provided the key evidence for our African origins,
8:21
to narrow down the location,
8:23
we need to look at entire genomes.
8:25
We can compare DNA from living populations with DNA samples
8:29
collected from ancient bones and tissues!
8:32
If we want to find the oldest consecutive lineage of humans,
8:35
we look for the people who are more genetically diverse
8:38
than any other group on Earth.
8:40
The most genetically diverse population of all modern humans
8:43
that we know of are Khoe-San people,
8:46
which is a group that includes the San hunter-gatherers
8:49
and Khoekhoe pastoralist herders,
8:52
both of whom mainly live in
8:53
South Africa, Namibia, Botswana, Angola, Zambia, Zimbabwe,
8:58
and Lesotho.
8:59
The term Khoe-San can be sort of controversial depending on who you ask,
9:03
since it’s kind of a catch-all for a few different ethnic groups.
9:07
So for our purposes,
9:08
we’ll refer to the folks we’re talking about as the Khoekhoe and San people.
9:12
And their genetics tell quite the story.
9:15
Their L0 mitochondrial DNA lineages
9:18
are the oldest ones we’ve found in any living humans,
9:21
and their chromosomal DNA is chock full of variation, too.
9:25
So, since the Khoekhoe and the San people live in southern Africa,
9:29
you might think we have the whole thing solved.
9:31
We must come from there!
9:32
But there’s a twist.
9:34
See, they live in southern Africa today,
9:36
but early studies of their mitochondrial DNA
9:39
suggested they didn’t necessarily start there.
9:42
One study mapped migrations through Africa based on haplogroups,
9:46
and found that the L0 haplogroup
9:48
was found to have the highest diversity and highest frequency
9:52
in southeast and east Africa.
9:55
Given that highest variation often means earliest divergence,
9:58
this suggested an eastern birthplace of modern humans.
10:02
So for the umpteenth time we have to say there’s more to the story.
10:05
Mitochondrial DNA works great to demonstrate our movement out of Africa,
10:10
since we’re only dealing with L3-derived haplogroups.
10:13
But tracking movement using mitochondrial DNA is less clearcut within Africa
10:19
when a lot of other ancient haplogroups are in play.
10:21
Humans made pretty dramatic movements
10:23
over the last few thousand years
10:25
which spread and diversified the original L haplogroups across Africa,
10:30
making it harder to trace their specific places of origin.
10:34
So the mitochondrial diversity of eastern Africa
10:37
might have been influenced by a lot more recent events than it first appears.
10:41
And that’s why it’s important to look beyond just the mitochondrial DNA, a
10:46
nd go all in on genome analysis.
10:48
Instead of just using DNA from African populations alive today,
10:52
a study published in Nature in December 2025 sequenced whole genomes
10:57
of 28 archaeological individuals from southern Africa,
11:01
who were alive between 10,200 and 150 years ago.
11:06
This technique helped to sort out what genetic material
11:09
was a more recent addition to the gene pool,
11:12
as even a relatively short jump back in time clears out
11:16
a lot of modern-day gene swapping.
11:18
And they realized that the ancient genomes
11:20
had a ton of genetic variants that aren’t around in humans today,
11:25
even in the highly diverse genomes of the Khoekhoe and San peoples.
11:29
It would appear that these southern ancestors branched off f
11:32
rom essentially all other human populations somewhere
11:35
between 310 to 240 thousand years ago,
11:40
back when we would have considered Homo sapiens to be in their early,
11:43
and not modern stage.
11:45
This southern African group also appeared to stay very isolated f
11:49
rom other Homo sapiens populations for a long time.
11:53
It’s possible that environmental conditions were to blame,
11:56
preventing their expansion beyond the southernmost region of Africa.
12:00
But it clearly worked in their favor.
12:01
The conditions they faced during that long period of isolation
12:05
propelled them to perfect the modern human toolkit;
12:09
complete with hearty immune systems, UV-protected skin,
12:12
and upgraded kidneys.
12:14
Not only that, several of the gene variants
12:17
unique to this ancient southern African population
12:19
were tied to brain growth, neurons,
12:22
and how the brain processes information.
12:25
These specific adaptations would set this population apart
12:28
not only from our Neanderthal and Denisovan cousins,
12:31
but from the rest of our own species still living elsewhere in Africa.
12:35
Eventually some of those immune-savvy brainiacs
12:38
took their specialized gene pool north
12:41
to join the rest of our Homo sapiens populations,
12:44
likely in small-ish bursts over a longer period of time as milder conditions
12:49
allowed them to leave the south.
12:50
Those genes ended up being so important to our species’ survival,
12:54
they would have infiltrated much of existing early human gene pools across Africa,
12:59
spreading them to the broader human population.
13:02
Some of these modern southern Africa humans likely stayed
13:05
closer to home in the south,
13:07
which explains why the ancestors of the Khoekhoe and San peoples
13:11
have retained a lot more of our original genetic variation.
13:14
So today’s Khoekhoe and San peoples
13:17
might still be the closest tie to our southern African start,
13:20
despite having lost around 20% of their ancient ancestors’ DNA
13:25
over the last few centuries.
13:26
Of course, these DNA results and hypothetical models
13:30
still leave us with a very inconclusive origin story overall.
13:34
That said, it appears that southern Africa
13:36
could be the location that really pushed us
13:38
to become our modern human selves:
13:40
anatomically, behaviorally, and genetically.
13:44
While we still don’t have a definitive answer
13:46
for exactly where in Africa we originated,
13:49
the more we look into our own DNA,
13:51
the more we reveal about ourselves.
13:54
It can not only help us figure out the wheres and whens,
13:56
but also reveal really interesting aspects of our history,
14:00
like what were some of the specific conditions and pressures we faced
14:04
to evolve our immensely useful brains.
14:07
One thing is certain,
14:08
we humans covered a lot of ground from the very beginning.
14:11
So if you’re a wandering soul,
14:13
you’ve got that in common
14:14
with the very earliest members of our species.
14:18
[ OUTRO ]
Where Are Humans ACTUALLY From? - Video học tiếng Anh
