The Astoria section of Queens, New York, is one of the most ethnically diverse communities on Earth. At the 30th Avenue Street Festival in July 2008, people of all heritages and complexions mingled among booths offering up Thai charms and Peruvian sweaters, Mexican corn and Italian zeppole. The sun was hot, the mood merrily multicultural. Through the crowd walked a tall, blond man with pale skin rapidly turning red. He stopped occasionally to talk to people, and if he found them obliging, asked if they could spare a few cells from the inside of their cheeks.
For the past four years Spencer Wells and his colleagues with National Geographic and IBM’s Genographic Project have been traveling the globe, collecting DNA in cheek swabs and blood samples from hundreds of indigenous groups. By comparing their DNA, the project has been retracing the ancient history of human migrations since our species originated in Africa some 200,000 years ago.
The Genographic Project focuses on the Y chromosome in males, which is handed down intact from father to son, and on mitochondrial DNA (mtDNA), which a mother passes to her offspring. Over generations, small, harmless mutations accumulate on these two snippets of DNA; to Wells and other scientists these genetic markers constitute a history book.
As ancient human populations migrated out of Africa, splitting off from each other and entering new lands, they accumulated different patterns of markers that reflect that history. Each individual today retains such a pattern.
In recent centuries those prehistoric paths have reconnected in New York and other immigrant havens. “From the beginning of the project,” Wells says, “I’ve wondered if it would be possible to sample all the major lineages on Earth on a single street.” On 30th Avenue he almost did—the 193 volunteers turned out to be carrying genetic markers for virtually all the major migrations that peopled the continents.
The only missing lineage was the oldest one, which Genographic scientists found in Khoisan hunter-gatherers in southern Africa; their ancestors initially diverged from other modern humans more than 100,000 years ago.