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 Water forms 'spine of hydration' around DNA, group finds
26.05.2017 | Cornell University

nachricht How herpesviruses win the footrace against the immune system
26.05.2017 | Helmholtz-Zentrum für Infektionsforschung

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Can the immune system be boosted against Staphylococcus aureus by delivery of messenger RNA?

Staphylococcus aureus is a feared pathogen (MRSA, multi-resistant S. aureus) due to frequent resistances against many antibiotics, especially in hospital infections. Researchers at the Paul-Ehrlich-Institut have identified immunological processes that prevent a successful immune response directed against the pathogenic agent. The delivery of bacterial proteins with RNA adjuvant or messenger RNA (mRNA) into immune cells allows the re-direction of the immune response towards an active defense against S. aureus. This could be of significant importance for the development of an effective vaccine. PLOS Pathogens has published these research results online on 25 May 2017.

Staphylococcus aureus (S. aureus) is a bacterium that colonizes by far more than half of the skin and the mucosa of adults, usually without causing infections....

Im Focus: A quantum walk of photons

Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.

The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....

Im Focus: Turmoil in sluggish electrons’ existence

An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.

We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...

Im Focus: Wafer-thin Magnetic Materials Developed for Future Quantum Technologies

Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.

Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...

Im Focus: World's thinnest hologram paves path to new 3-D world

Nano-hologram paves way for integration of 3-D holography into everyday electronics

An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Marine Conservation: IASS Contributes to UN Ocean Conference in New York on 5-9 June

24.05.2017 | Event News

AWK Aachen Machine Tool Colloquium 2017: Internet of Production for Agile Enterprises

23.05.2017 | Event News

Dortmund MST Conference presents Individualized Healthcare Solutions with micro and nanotechnology

22.05.2017 | Event News

 
Latest News

How herpesviruses win the footrace against the immune system

26.05.2017 | Life Sciences

Water forms 'spine of hydration' around DNA, group finds

26.05.2017 | Life Sciences

First Juno science results supported by University of Leicester's Jupiter 'forecast'

26.05.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>