Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Man left Africa three times

07.03.2002


Early humans came out of Africa again and again.

There were at least three major waves of early human migration out of Africa, our DNA suggests. Apparently the wanderers made love, not war: gene patterns hint that later emigrants bred with residents.

Human origins are contentious. Most researchers agree that there have been several major migrations out of Africa. Some hold that human populations in many regions evolved in parallel after Homo erectus left Africa around two million years ago. Others think that a wave of modern humans from Africa replaced all previous Eurasian populations perhaps as recently as 50,000 years ago.



The truth lies somewhere in the middle, proposes geneticist Alan Templeton of Washington University, St Louis1. "Africans have had a huge genetic impact on humanity," he says. "But my analysis really isn’t compatible with complete replacement."

But this will not be the last word on the matter. Researchers are divided over what sorts of genetic information are most useful, and how it should be analysed. Believers in the replacement hypothesis remain unconvinced by Templeton’s arguments.

Moving story

Templeton compared DNA sequences of populations around the world. He combined information from ten genetic regions on regular chromosomes, sex chromosomes and mitochondria, the cellular powerhouses with their own genomes. By analysing many different genes, he hoped to clarify the sometimes contradictory results from individual sequences.

Variation in genes from different places enabled him to reconstruct the story of human movement. He saw where particular mutations arose, and how they spread through mating or migration.

Templeton’s reading of the genetic runes is that, post Homo erectus’ exit, there was a second major human migration out of Africa between 400,000 and 800,000 years ago and a third about 100,000 years ago. He also sees a more recent movement back into Africa from Asia, and huge amounts of genetic interchange between groups.

And this is just a start. "It’s the big picture on a very coarse timescale," Templeton says. "The potential for adding more details is truly immense."

Jury’s out

"It is very significant work - it fits the genetic, fossil and archaeological evidence," says anthropologist Jonathan Relethford of the State University of New York, Oneonta.

But geneticists who believe that recent African emigrants replaced older Eurasian populations remain sceptical. This hypothesis is based on studies of mitochondrial and Y-chromosome DNA. Martin Richards, of the University of Huddersfield, UK, who did some of these studies, thinks that genes on normal chromosomes, called autosomes, only confuse the picture.

"The data from autosomal genes are very, very impoverished," he says. The picture the Y chromosome gives, on the other hand, is "absolutely watertight", he says.

"The tree’s root is in Africa, and one branch contains all the non-Africans," says Richards. "You don’t get deeper lineages popping up all over the world."

Some archaeologists also dispute Templeton’s conclusions. Richard Klein, of Stanford University, California, says there is scant archaeological evidence of a permanent human presence in Europe before 500,000 years ago. Migrants before this point "may have found no one to interbreed with".

References
  1. Templeton, A. R. Out of Africa again and again. Nature, 416, 45 - 51, (2002).


JOHN WHITFIELD | © Nature News Service

More articles from Life Sciences:

nachricht Bacteria as pacemaker for the intestine
22.11.2017 | Christian-Albrechts-Universität zu Kiel

nachricht Researchers identify how bacterium survives in oxygen-poor environments
22.11.2017 | Columbia University

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Nanoparticles help with malaria diagnosis – new rapid test in development

The WHO reports an estimated 429,000 malaria deaths each year. The disease mostly affects tropical and subtropical regions and in particular the African continent. The Fraunhofer Institute for Silicate Research ISC teamed up with the Fraunhofer Institute for Molecular Biology and Applied Ecology IME and the Institute of Tropical Medicine at the University of Tübingen for a new test method to detect malaria parasites in blood. The idea of the research project “NanoFRET” is to develop a highly sensitive and reliable rapid diagnostic test so that patient treatment can begin as early as possible.

Malaria is caused by parasites transmitted by mosquito bite. The most dangerous form of malaria is malaria tropica. Left untreated, it is fatal in most cases....

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

Corporate coworking as a driver of innovation

22.11.2017 | Business and Finance

PPPL scientists deliver new high-resolution diagnostic to national laser facility

22.11.2017 | Physics and Astronomy

Quantum optics allows us to abandon expensive lasers in spectroscopy

22.11.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>