My Blood Brother in Samarkand

One morning last spring I steered a Land Rover off the Chunnel train and onto a French freeway. Stuffed in back were hypodermic needles, tourniquets and chemical powders. My companion and I had bought cheap single-day return tickets, neglecting to mention that we'd likely miss the late train back to England.

We were driving to the Chinese border instead. And we were out for blood.

Two tablespoons of blood yield enough DNA to add a person's genetic information to a growing database of human diversity. As population geneticists, Spencer Wells and I were working with Stanford emeritus professor Luca Cavalli-Sforza and others to study DNA variation among different groups. Our mission: use genetic clues to fill in missing pieces in the puzzle of human history. But first, we needed more blood.

Our expedition eventually took us through the forests, steppes and deserts between the Black Sea and Central Asia's Altai Mountains. We collected hundreds of samples from people whose ancestors included nomads, farmers, sultans and serfs and whose genetic makeup had been shaped for millennia by waves of conquest and trade in this region of the Silk Road.

At one level, our research plumbs unique histories of specific groups. But when we look beyond those often-intriguing tales, a broader conclusion becomes clear: we're all more closely related than people realize.

I learned this personally when, crossing sunbaked Uzbekistan, our expedition rolled into the old oasis city of Samarkand.

Back at Stanford, my labmates and I had compared hundreds of DNA samples from men around the world, focusing on about a dozen sites along the Y chromosome. Because the Y passes largely unchanged from father to son, any site-for-site match of DNA sequences between two samples suggested that those two men shared a recent male-line ancestor. In fact, their common forefather likely lived within the last thousand years or so -- an eyeblink in evolutionary terms.

Out of curiosity, I submitted my own sample to the database -- and discovered that I matched with four other donors. One was a Turkic-speaking man in western Uzbekistan, two lived in New Delhi, and one was a Tajik living in Samarkand.

Such matches aren't terribly unlikely, depending on where you're from. Still, I was surprised and intrigued, and I decided to look up the Samarkand man, Sharif S., while collecting samples in Uzbekistan.

With just his name and age to go on, I learned where he lived and soon found myself knocking on his door, wondering how to explain this bizarre visit. Sharif's wife welcomed me into a leafy courtyard and listened patiently to my story. Unluckily for us, she said, Sharif was off exploring America. Disappointed, I wondered if some gene on the Y chromosome provoked intercontinental wanderlust.

I reassured Sharif's wife that despite all the chromosome malarkey I was not her husband's unknown American son. His actual son was home, however, and he proudly produced snapshots of his dad. Maybe it's a stretch, I thought, but the man in the photos could pass for an uncle in my family.

The Y is a big chunk of DNA to have in common. How in the world had Sharif and I come to share that inheritance?

History suggests a few possibilities. Sharif's Tajiks are Persian-speakers who moved east to Samarkand well before the arrival of Islam there about 1,300 years ago and the heyday of overland trade. They mixed with people already there and, later, with Turkic immigrants and others. My recent ancestors were Ashkenazi Jews in Ukraine; that population likely moved by several routes from the Middle East to Eastern Europe over the past couple of thousand years, mixing with Indo-European and Turkic people along the way. The common influence of Indo-European, Semitic and Turkic ancestry is one clue to how we might share a recent ancestor. That both Jews and Tajiks plied the Silk Road about a thousand years ago is another.

Maybe the DNA gathered on our expedition will solve such little mysteries, along with bigger ones. In five months, we managed to sample a remarkable human mosaic, bringing back no silk, but plenty of blood.