for National Geographic News
By analyzing DNA from people in all regions of the world, geneticist Spencer Wells has concluded that all humans alive today are descended from a single man who lived in Africa around 60,000 years ago.
Modern humans, he contends, didn't start their spread across the globe until after that time. Most archaeologists would say the exodus began 100,000 years ago—a 40,000-year discrepancy.
Wells's take on the origins of modern humans and how they came to populate the rest of the planet is bound to be controversial.
His work adds to an already crowded field of opposing hypotheses proposed by those who seek answers in "stones and bones"—archaeologists and paleoanthropologists—and those who seek them in our blood—population geneticists and molecular biologists.
Over the last decade, major debate on whether early humans evolved in Africa or elsewhere, when they began outward migration, where they went, and whether they interbred with or replaced archaic species has moved out of scientific journals and into the public consciousness.
Wells addresses these issues in a new book, The Journey of Man: A Genetic Odyssey, and a National Geographic documentary of the same title. In a straightforward story, he explains how he traced the exodus of modern humans from Africa by analyzing genetic changes in DNA from the y-chromosome.
"As often happens in science," he said, "technology has opened up a field to new ways of answering old questions—often providing startling answers."
Of course, not everyone agrees with him.
Search for Origins
The use of population genetics and molecular biology in human origins research has been extremely important in helping to resolve a long-running debate on where modern humans first evolved.
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