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Published online:
29 September 2004; | doi:10.1038/news040927-10
Human populations are tightly
interwovenMichael
Hopkin
Family tree
shows our common ancestor lived just 3,500 years
ago.
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The person from whom everyone
today is descended may have lived around 1,500
BC. ©
Getty | | The most recent common ancestor of
all humanity lived just a few thousand years ago, according to
a computer model of our family tree. Researchers have
calculated that the mystery person, from whom everyone alive
today is directly descended, probably lived around 1,500 BC in
eastern Asia.
Douglas Rohde of the Massachusetts
Institute of Technology in Cambridge and his colleagues
devised the computer program to simulate the migration and
breeding of humans across the world. By estimating how
different groups intermingle, the researchers built up a
picture of how tightly the world's ancestral lines are
linked.
The figure of 1,500 BC might sound
surprisingly recent. But think how wide your own family tree
would be if you extended it back that far. Lurking somewhere
in your many hundreds of ancestors at that date is likely to
be somebody who crops up in the corresponding family tree for
anyone alive in 2004.
In fact, if it were not for the
fact that oceans helped to keep populations apart, the human
race would have mingled even more freely, the researchers
argue. "The most recent common ancestor for a randomly mating
population would have lived in the very recent past," they
write in this week's Nature1.
Striking out
To work out how much
different groups of humans mingled, Rohde's team simulated the
rates at which a few pioneering people made journeys across
the world to meet and breed with other populations. Their
model gave each individual a certain probability of quitting
their home town, country or continent and striking out for
pastures new.
They were then able to name a time
and place at which our most recent common ancestor lived. But
who was this person? He or she must have had a flourishing
family, says Rohde. "Maybe it was someone who happened to have
40 children or some such astronomical number," he says. "But
it could equally have been someone with above-average
productivity for a few generations." Instead of two kids,
Rohde suggests, maybe the person and his or her direct
descendants had three.
The fact that the person probably
lived in Asia is down to its prime position along the most
commonly used migration routes, Rohde suggests. "East Asia is
at a crossroads," he says. "It's close to the Bering Strait
and the Pacific."
No isolation
Rohde's
simulation aims to include everyone alive today, and therefore
relies on the assumption that no population has remained
completely isolated for any significant length of time. Rohde
is confident that this is the case; even Tasmania, once
thought to be isolated by choppy seas, contains no people with
purely Tasmanian blood.
If we discount those living in the
world's remotest places, the common ancestor becomes more
recent still, says Mark Humphrys, who studies human family
trees at Dublin City University in Ireland. "Looking at the
whole sweep of the Americas, Europe, Asia, right across to
Japan, I wouldn't be surprised if we had a common ancestor in
the AD years," he says.
A single prolific parent can have a
vast influence once their descendants begin to multiply,
Humphrys says. "The entire Western world is descended from
Charlemagne, for example," he says. "There's really no
doubt."
All or nothing
Besides
dating our most recent common ancestor, Rohde's team also
calculates that in 5,400 BC everyone alive was either an
ancestor of all of humanity, or of nobody alive today. The
researchers call this the 'identical ancestors' point: the
time before which all the family trees of people today are
composed of exactly the same individuals.
This
recent date is not really surprising either, Rohde says.
Anyone whose lineage survived for a few generations was likely
to have descendants spread all over the world. At the
identical ancestors point, then, our ancestors came from every
corner of the globe, although those from far afield are
unlikely to have made a significant contribution to our
genetic make-up.
Nonetheless, the results show that
we are one big family, Rohde says. As he and his colleagues
write: "No matter the languages we speak or the colour of our
skin, we share ancestors with those who planted rice on the
banks of the Yangtze, who first domesticated horses on the
steppes of the Ukraine, who hunted giant sloths in the forests
of North and South America, and who laboured to build the
Great Pyramid of Khufu."
References
- Rohde D. L. T, Olson S. & Chang
J. T. Nature, 431, 562- 565.
(2004). | Article |
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Story from
news@nature.com:
http://news.nature.com//news/2004/040927/040927-10.html | |
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