VOA标准英语2009-Study Unlocks Genetic Diversity in Africa（在线收听）

A group of scientists has unveiled what they say is the most comprehensive study ever of African genes which they say gives new insight into the origins of humans.

The genetic study, a compilation of two big studies, confirms theories that modern humans evolved in Africa and then migrated through Europe and Asia to reach the Pacific and Americas. The study also shows that Africans have the most diverse DNA, and the fewest potentially harmful genetic mutations.

Published in the US journal Science, researchers examined genetic material from 121 African populations, as well as four African-American populations and 60 non-African populations. The study aims to teach Africans on population history and aid research into why diseases hit particular groups.

The researchers found that after a population of humans migrated off the African continent, the group shrank for some unknown reason. Later populations grew and spread from this smaller genetic pool of ancestors.

Populations that remained in Africa kept their genetic diversity.

Sarah Tishkoff, a geneticist from the University of Pennsylvania, says the results provided insights about levels and patterns of genetic diversity in Africa. "That population had the highest levels of mixed ancestry on a global level. So, they had almost equal proportions of ancestry from Europeans. They also showed ancestry from East Asia, probably reflecting Southeast Asian ancestry, a little bit of Oceanic ancestry as well as south Indian ancestry," she said.

Widespread migrations also occurred on the continent itself, according to researchers who identified 14 ancestral population clusters who one time shared the same cultural characteristics and spoke the same languages.

The study of African diversity promises to provide valuable information in the field of biomedicine.

Scott Williams is a co-author of the study and a professor of biophysiology at Vanderbilt University in Tennessee. He says researchers will be able to trace diseases to certain Africa populations to help researchers understand their cause, with an eye toward developing treatments. "The examples that certainly I'm familiar with relate to diseases that are common in people of West African origin such as hypertension (and) prostate cancer. And some of these studies are ongoing in parts of West Africa," he said.

Tishoff says that the goal of the study is to benefit Africans, both by learning more about their population history and by setting the stage for future genetic studies, including studies of genetic and environmental risk factors for disease and drug response. "We don't want to see Africa populations get left behind in this genomic revolution. And so we hope this will stimulate further studies in Africa," she said.

The study also found that people of African descent are the most genetically diverse, followed by people from the Middle East, and then Asians and Europeans. Native Americans resemble one another the most on a DNA level.