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 Bare bones: Making bones transparent
27.04.2017 | California Institute of Technology

nachricht Link Discovered between Immune System, Brain Structure and Memory
26.04.2017 | Universität Basel

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

Bare bones: Making bones transparent

27.04.2017 | Life Sciences

Study offers new theoretical approach to describing non-equilibrium phase transitions

27.04.2017 | Physics and Astronomy

From volcano's slope, NASA instrument looks sky high and to the future

27.04.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>