Gene studies confirm ‘out of Africa’ theories

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Gene studies confirm `out of Africa' theories

Findings: Africans also have most diverse DNA, fewest genetic

mutations

http://www.msnbc.msn.com/id/23261247/

By Maggie Fox

Two big genetic studies confirm theories that modern humans evolved

in Africa and then migrated through Europe and Asia to reach the

Pacific and Americas.

The two studies also show that Africans have the most diverse DNA,

and the fewest potentially harmful genetic mutations.

One of the studies shows European-Americans have more small

mutations, while the others show Native Americans, Polynesians and

others who populated Australia and Oceania have more big genetic

changes.

The studies, published in the journal Nature on Wednesday, paint a

picture of a population of humans migrating off the African

continent, and then shrinking at some point because of unknown

adversity.

Later populations grew and spread from this smaller genetic pool of

founder ancestors — a phenomenon known as a bottleneck.

Populations that remained in Africa kept their genetic diversity —

something seen in many other studies.

" The one thing that I think we cannot say from this study is that any

one person's genome is any healthier or evolutionarily fit than

another person's genome, " said Bustamante of Cornell

University in New York, who worked on one study.

" You have to think of this at the population level, " Bustamante said

in a telephone interview.

Fit or extinct

Bustamante's team has been looking at the DNA sequences of 15 African-

Americans and 20 European-Americans, examining tiny one-letter

changes in the DNA code called single-nucleotide polymorphisms or

SNPs (pronounced " snips " ).

They tested these changes to qualify them as benign, or potentially

affecting genes, amino acids and eventually proteins in a way that

could damage health or make people less " fit " — in evolutionary

terms, less likely to survive and reproduce.

" Like every other study ... the African-American panel as a whole

showed more variation than the European-American panel, " Bustamante

said.

Then his team did a computer simulation of a bottleneck, and found it

predicted this pattern.

Bustamante said it is possible some of the SNPs are beneficial, and

he said his team and others should compare the genetic changes they

found to known genetic changes linked with diseases.

" I wish we had done that (already), " he said.

Genetic variations

In the other study, Noah Rosenberg and colleagues at the University

of Michigan and the National Institute on Aging analyzed DNA from 485

people around the world.

They looked for three types of genetic variation, including SNPs and

larger changes that involve duplications, deletions and repetitions

of large segments of DNA.

The patterns they found produced what they call the highest-

resolution map yet of human genetic variation.

They also reinforce the idea that humans originated in Africa, then

spread into the Middle East, followed by Europe and Asia, the Pacific

Islands and finally to the Americas.