SCI/TECH: National Geo & IBM Trace Human Migration via Genes

The X and Y chromosomes carry the genes that determine sex. Men have one X, inherited from their mothers, and one Y, inherited from their fathers. Only 5 percent of the Y chromosome’s DNA mingles with the X chromosome. The Y thus provides an unadulterated record of inheritance from father to son over generations. By analyzing Y chromosome samples from around the world, geneticists infer how and when humans originated in Africa and how they colonized the globe.

To each donor or group of donors, Wells gave what he calls his blood speech, explaining DNA, the purpose of the expedition, their role in it, and then asking for “informed consent.” On the television version of The Journey of Man, for which Wells traveled the world in 2002, retracing some of his earlier steps, he visits a man in southeastern Kazakhstan whose blood had been sampled on the 1998 expedition and who has turned out to have an important Y chromosome marker called M45. At a festive dinner, Wells gives him the blood speech again and concludes with a toast: “To your very important blood, which has brought us together.” The man seems happy and relieved: As Wells candidly explains, he thought Wells had come back to tell him he had cancer.

Scenes like that demonstrate that truly informed consent can be an elusive goal in anthropological genetics, and yet it seems clear that Wells has done no harm to the man and has done our knowledge of the past a lot of good. M45 is an important branching point on the human family tree. One branch leads to M173, which is a mutation shared by most people of Western European descent. The other branch leads to M3, which is shared by most Native Americans. European and Native American men also have M45, but in Central Asia there are men, like Wells’s Kazakh dinner companion, who have M45 but neither of the two later mutations—they have a large range of different ones instead. That indicates Central Asia is where M45 originated and where both Europeans and Native Americans originated, from a single source.
 
By counting the number of mutations that have happened since M45, Wells and his colleagues estimate that M45 is about 35,000 to 40,000 years old. The European marker, M173, happened roughly 30,000 years ago, which is when the first cave paintings appeared in France. M3 is present only in Native Americans, and so it must have happened after humans first crossed the Bering Strait and arrived in the Americas. Archaeologists have long debated the timing of that momentous event; most favor a date of around 13,000 or 14,000 years ago, but a few have held out for one as early as 30,000 years ago.

I do not know if someone has told you this yet but thereis a thread on this already