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| Photograph by Joe McNally, National Geographic "Come at me bro" |
(National Geographic.com, 12, Oct 2012) - Well, not exactly. But new discoveries have had a
surprisingly humanizing effect.
The Neanderthals are both the most familiar and the least understood
of all our fossil kin.
For decades after the initial discovery of their bones in a
cave in Germany in 1856 Homo neanderthalensis was viewed as a hairy brute who
stumbled around Ice Age Eurasia on bent knees, eventually to be replaced by
elegant, upright Cro-Magnon, the true ancestor of modern Europeans.
Science has long since killed off the notion of that witless
caveman, but Neanderthals have still been regarded as quintessential losers—a
large-brained, well-adapted species of human that went extinct nevertheless,
yielding the Eurasian continent to anatomically modern humans, who began to
migrate out of Africa some 60,000 years ago.
Lately, the relationship between Neanderthals and modern humans
has gotten spicier.
According to a new study that analysed traces of Neanderthal
DNA in present-day humans, Neanderthals may have been interbreeding with some
of the ancestors of modern Eurasians as recently as 37,000 years ago. And
another recent study found that Asian and South American people possess an even
greater percentage of Neanderthal genes.
"These are complexities in the out-of-Africa story that
certainly I would not have anticipated two or three years ago," said Chris
Stringer, a paleoanthropologist at the Natural History Museum in London and
author of Lone Survivors: How We Came to Be the Only Humans on Earth.
In their original incarnation, Neanderthals were viewed as
the primitive, backward cave dwellers of Eurasia, far less complex than the
sophisticated Homo sapiens who used language and developed sophisticated art as
they migrated out of Africa and conquered the world.
But new studies are making it much harder to draw a clean
line between us and them.
"It's increasingly difficult to point to any one thing
that Neanderthals did and Homo sapiens didn't do and vice versa," said
John Shea, an archaeologist at Stony Brook University in New York.
"These Ice Age people, both Neanderthals and Homo
sapiens, survived, thrived, and increased their numbers under conditions that
would probably kill people nowadays, even ones that are equipped with modern
survival technology."
The draft sequence of the Neanderthal genome, published in
the journal Science in 2010, provided the first compelling genetic evidence
that Neanderthals and H. sapiens had more in common than just an ancestor in
Africa hundreds of thousands of years ago.
The researchers, under the direction of Svante Pääbo of the
Max Planck Institute for Evolutionary Anthropology, found that 2.5 percent of
the genome of an average human living outside Africa today is made up of
Neanderthal DNA. The average modern African has none.
This suggested that some interbreeding had taken place
between the two kinds of human, probably in the Middle East, where the early
modern humans migrating out of Africa would have encountered Neanderthals
already living there.
The even larger percentage of Neanderthal DNA found in
Asians and South Americans, announced in Science in August, could indicate
additional interbreeding in Asia long ago, or could mean that the percentage of
Neanderthal DNA in Europeans was diluted by later encounters.
Not everyone is convinced that interbreeding was responsible
for similarities in the Neanderthal and H. sapiens genomes. "The
similarities they're seeing may be ancient," Shea noted.
Another recent study, published in the journal Proceedings
of the National Academy of Sciences in August, calculated that the shared DNA
could have come from an earlier, common ancestor of Neanderthals and H.
sapiens—no hanky-panky necessary.
A new study by Pääbo's team, published last week in PLOS
Genetics, also considered the possibility that the presence of Neanderthal DNA
in people living outside Africa today could be traced far back, to the common
ancestor of both Neanderthals and modern humans in Africa.
Perhaps the early modern humans who left Africa 60,000 years
ago were already genetically more similar to the Neanderthals—who had left
hundreds of thousands of years before—than were the modern human populations
that stayed behind in Africa. In that case, no interbreeding would have needed
to occur to account for the trace of Neanderthal DNA in non-Africans today.
To test the two hypotheses, Pääbo's group analyzed the
lengths of segments of Neanderthal DNA in modern Europeans to determine when
Neanderthal genes may have mixed with those of modern humans. The date they came
up with for the gene flow was 37,000 to 86,000 years ago, and most likely
47,000 to 65,000 years ago.
This date strongly suggests there was indeed interbreeding
between "us and them," when H. sapiens was moving into the Middle
East from Africa and would have encountered populations of Neanderthals already
settled there.
"This [interbreeding] could have been a really powerful
mechanism for humans to adapt as they moved into Eurasia," said Sriram
Sankararaman, a statistical geneticist at Harvard Medical School and the lead
author of the PLOS Genetics study.
Another group, publishing last year in Science, for example,
determined that modern humans gained from Neanderthals a family of genes that
helps the immune system fight off viruses. Breeding with the locals could have
unwittingly given H. sapiens a survival advantage in a new land.
"[Neanderthals] are not just some extinct group of
related hominids," Pääbo said. "They are partially ancestors to
people who live today."
Take any two unrelated humans today, Pääbo noted, and
they'll differ in millions of places in their genetic code. But the Neanderthal
genome varies on average from that of H. sapiens in only about a hundred
thousand positions. Pääbo and his colleagues are now trying to figure out the consequences
of those differences.
Regardless of the similarities to our DNA, how
"human" were Neanderthals in their sensibilities?
Last month a study led by the Gibraltar Museum and published
in PLOS ONE documented a multitude of fossil remains of bird wings,
particularly from big black raptors, at Neanderthal sites in southern Europe.
The team suggested that Neanderthals could have been plucking feathers from the
wings for personal use or even for ritual ornaments.
"We have other evidence for Neanderthals preferring
mineral pigments that are dark, blackish color," Stony Brook's Shea said.
"There may be something for them with the color black just as there seems
to be something for us with the colour red."
Sophisticated art, however, still appears to remain in the
realm of H. sapiens.
The ancestors of modern humans left behind images of animals
and other objects in caves around the world, most famously at Lascaux cave and
Chauvet Cave (pictures) in southern France. Paintings in the latter cave could
be as ancient as 37,000 years old. (See a prehistoric time line.)
Images found in a cave called El Castillo on the Spanish
coast were recently dated at more than 40,800 years old: a time before
Neanderthals disappeared, raising the tantalizing possibility that they were
indeed the artists. However, "it hasn't been demonstrated that
Neanderthals produced any of that cave art," the Natural History Museum's
Stringer said.
The simpler answer is that H. sapiens, who had also reached
Europe by that time and are known to have produced later but similar art, were
responsible.
Neanderthals, though, have proven advanced in other ways.
They used pigments and may have made jewellery; some made
complex tools. "We know they buried their dead," Stringer said. In
2010, researchers from the Smithsonian Institution even found evidence that the
Neanderthal diet included a diverse mixture of plants, and that they cooked
some of the grains.
"Cooking something like oatmeal is not what we would
have imagined," said John Hawks, paleoanthropologist at the University of
Wisconsin-Madison. With no pots, Neanderthals may have cooked inside leaves,
Hawks suggested. "That starts to sound like cuisine."
"Neanderthals have gone from being different from us to
being like us," Hawks noted. "They're looking like [Homo sapiens]
hunter-gatherers look."
But while modern humans continued to develop cultural
complexity and spread across the globe, the Neanderthals vanished. Why remains
a mystery.
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