How are all of the species living on Earth today related? How does understanding evolutionary science contribute to our well-being? In this course, participants will learn about evolutionary relationships, population genetics, and natural and artificial selection. Participants will explore evolutionary science and learn how to integrate it into their classrooms.
H. neanderthalensis, H. sapiens and the Peopling of the World
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Do curso por American Museum of Natural History
Evolução: Um Curso para Educadores
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Human Evolution
This module explores the rich variety of hominids on the tree of life, along with how and when different human species - including Homo sapiens - migrated around the world. You’ll also learn strategies for teaching evolution in culturally diverse classrooms.
Conheça os instrutores
Joel Cracraft, Ph.D.Chair and Lamont Curator
Division of Vertebrate Zoology
David Randle, Ph.D.Senior Manager of Professional Development
Education Department
This lecture is about peopling of the world,
that is, many species went and left Africa.
Homo erectus left very early, over a million
years ago and and speciated in Southeast Asia.
Neanderthals apparently speciated in Western Eurasia.
And Homo sapiens left Africa multiple times and then,
eventually, found its way across the Bering land bridge
into North America and then into South America.
This, this picture shows, in green, all of the species
that have made it to the northern hemisphere.
So Erectus got up very early. Georgicus, which we
talked about a little bit in in the last lecture, has been
found in the Republic of Georgia at around
1.7 million years and antecessor is in Spain.
Neanderthals got out, so did Homo sapiens and their
[UNKNOWN]
common ancestor, Heidelbergensis, got out of Africa
and also has, has been found in Europe.
But we're going to turn some of our attention to this little creature right
here, floresiensis, because floresiensis is one of the most peculiar
finds in all paleoanthropology and it's a very recent find.
In Indonesia,
on the island of Flores. So here's
the Indonesian islands and here's the island of Flores.
Up in the mountains of Flores, are caves. So the Liang
Bua cave is there and inside that, that, that cave, in layers
of sediment, are many fossils, and not only of several humans,
but one of the most remarkable finds in recent years.
And this figure shows the stratigraphy of this cave.
At the base, at around 1 million years, there are these big
elephants, there are big komodo dragons and there are human beings
and they think these humans are probably Homo erectus.
There were hiatus, that is, there were times when there
was no sedimentation so there was no fossil record, but
when we go into the next strata from around 880,000
years ago down to 600,000 years ago, they find giant rats.
They still find fossil bones of humans, probably
Homo erectus and they keep finding elephants and
they keep finding komodo dragons. Then there was another hiatus
and another hiatus, and at around 17,000
years ago, they found another very
small hominin, now called Homo floresiensis.
And then, that went extinct, probably because of
a volcanic eruption that created this hiatus and it was then reinvaded
many thousands of years later by more modern humans.
And this is what Homo floresiensis looks like, and it's so small down
here compared to all these other species of homo that they called it the hobbit,
but if you look at its skull, It's clearly a homo.
It's got a very small brow ridge, it's got a flat face, it's got a big cranial
vault, but it doesn't have a very large brain because it's such a small animal.
This is how small it is.
This is an awesome picture because here is a floresiensis,
and then this is a giant stork was, that was also preserved in the cave
that they found floresiensis in.
Now let's switch back to Europe and let's
compare the two species that are probably the
most famous species of homo and that, of
course, is us, Homo sapiens and Homo neanderthalensis.
It was found over around 250,000 to 30,000 years
ago and it died out in Europe around 30,000 years ago.
It was very widely spread across Europe and into parts of Western Asia.
Homo sapiens, however, you know, started at 200,000 years
ago but genetic analysis suggests that that lineage separating
went back 700,000 years ago.
Even though the fossil record says it's not that old.
It's only maybe between 3 and 400,000
years ago that these things might have separated.
Now humans and neanderthals are very gene, genetically distinct.
Here's a graph of variation within Homo sapiens.
Here's a graph of variation within Homo sapiens and neanderthals.
So this is the distance.
This the genetic distance between neanderthals and humans.
So humans form a cluster, neanderthals form a cluster and then, this is just to
give you a reference of how distanced chimpanzees are from from humans.
So neanderthals were really genetically distinct but they looked very
similar to Homo sapiens. But there's a real interesting story here.
They're very genetically distinct.
No one thinks that they interbred very much at all in Europe.
No one knows exactly why neanderthals went extinct at 30,000 years.
Some think that,
well, it must have been the pleistocene
glaciations but they had survived glaciations before.
Some think it, well, they, they lost in the competition with the smarter
Homo sapiens, but there doesn't seem to be any really clear evidence of that.
What we do know, by 30,000 years, they had disappeared.
But they, as I said, spread very widely. And over in Europe is a cave,
and in that cave has been found some homin hominin fossils.
And little phalange, little tips of the fingers were found there.
And they have sequenced the genome from those little
pieces of bone and they found out that this
critter out here was very distinct genetically, but
related to neanderthals. So the root of the tree
goes here, and so this is the Denisovan because it's
that's where it's from, and this is modern more
recent neanderthals. But this Denisovan is very
old but they, are related to one another and
then they, in turn, are related to to Homo sapiens.
So, you can take to the bank that
Homo sapiens is a sister group to Homo neanderthalensis.
But now this creates a really interesting story that goes even further.
Human species, Homo sapiens spread all the way across Southern Asia
several different times and move toward Southeast Asia and move
toward New Guinea Australia region out into Pacifica.
They've compared the genetics of these creatures,
and this is what it seems to show.
Here are
Papua New Guinea, Bougainville Island, which is right next to New Guinea,
here are the non-African Homo sapiens and here are the African Homo sapiens.
So, here are the African, Homo sapiens, non-African Homo sapiens and this is a
multi-dimensional figure that says, to what species are the Denisovans,
these, these neanderthals out there, are most closely related?
Well, they seem to be more closely related to those people
who move down into Southeast Asia, deep into Southeast
Asia, with the Denisovans. And what people think was
that here are the normal neanderthals, and
they exchanged, there, there are a few incidences of gene exchange but no
major interbreeding at all and then the Denisovans are
sharing some features with Melanesians. But it's a
bigger story than that, and let, in here, in this complicated diagram,
we're picking out only one gene, the exon
44, the dystrophin gene. And we're looking at all the variants.
So all of these little lines here are variants,
haplotypes, of that gene. Neanderthals have
a cytosine right there in position one
and they have a guanine right here in position 31.
And there is a haplotype B006 that also shares that
neanderthal gene but also, it also shares this uniquely
with, with neanderthals. Now where is this haplotype found?
It's all over the world.
Virtually all people, other than Africans, have, have that.
It's been very, it's, it's found in many, many populations around the world.
Because Africans, of course, were isolated from the neanderthals and all
that movement of Homo sapiens, so they didn't pick of this gene.
But what people think is that at some time in the past,
as Homo sapiens were moving across Southern Asia,
some of them got up into a lower
part of Siberia and interacted with Denisovan neanderthals.
And there must have been some in, instances
of breeding and they picked up these markers.
Now this is not the only marker in Homo sapiens that
indicates that very isolated interbreeding but in a,
in a sense, all of us can, many of us can
go around and we can say, I'm also a little bit Neanderthal.
So as, wave after wave, there were many waves that came across here, and
the, some of them came up in here and they interacted with the Denisovans.
This is a, on the left hand side, this is a phylogenetic tree or a gene tree,
really, for a huge, huge number of Homo sapiens, modern humans.
And, the idea, the objective of this gene analysis is to try to understand how
people move into Asia and into Southeast
Asia and, eventually, moved over into North America.
It was a very complicated pattern.
Populations came into India, they moved over into
Southeast Asia and then they moved over out into Northeastern Siberia.
They moved down into the Malaysian region, in other words, the Philippine region.
Melanesians came down and, and got into Australia and New Guinea and then,
other groups came down this way and then moved out across the
Pacific because we now understand that the Polynesians
have some genetic connection with populations that are up
here in Southeast Asia and not with, not with Melanesians.
At the same time all this was happening, humans moved across the Bering region.
Now the, this is the Bering Sea but at various times that was exposed so
they must have come in at, at a time when there was the glaciations.
But there was, we now know that there was
a corridor either through the middle of the ice
sheets or along the coast and people prefer this
because we have a lot of archaeological evidence out in
Alaska.
And so they, they came down and, and got down in to the Americas,
and spread from there down through Middle America and into South America.
As I mentioned, groups, groups came in from Southeast
Asia, and moved across. The Melanesians
had come in very early, they were in Australia 55,000, maybe
60,000 and they were certainly in New Guinea by it, well into
30, 35,000 years. And the, this lineage, this genetic
lineage moved in and across into Polynesia.
And here's the interesting thing.
Along the way, these peoples picked up some Melanesian genes.
So the take home messages from this lecture are that there were many species
of homo that moved out of Africa and into Eurasia.
They started over a million years ago and
continued up until just tens of thousands of years ago.
And many of these lineages gave rise to new species.
So the neanderthals originated in Europe, as far
as we can tell, as well as things like
Homo antecessor, which diversified in this area of Spain
and Portugal, and then the most remarkable of all
of these, which comes from one of these very early lineages that came
out is Homo floresiensis, on the island of Flores in, in the Indonesian Archipelago.
And that seems to have been a species associated with Homo
erectus when it first came out over a million years ago.
But Homo floresiensis is very young. And then the only one of all
of those species, and there were many species
that we actually didn't even talk about the only
one that survived was Homo sapiens and it
spread around the world within the last 50,000 years.
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