Feature A grand National Geographic project aims to chart global human migration using DNA from living people.
Out of Africa
A grand National Geographic project that aims to chart global human migration using DNA from living people prompted Hamida Ghafour to investigate her own genetic roots and explore the fundamental question of our history: where are we from? Some call it the greatest story ever told. It began with one woman who lived on the African savannah about 150,000 years ago when human beings were just a small, vulnerable blip on a savage landscape. We were learning to talk and easy prey for the wild beasts that roamed the land.
The story continues today: 6.8 billion descendants of this woman's children who, more than 7,000 generations later, have clawed their way to the top of the food chain and are living on a crowded, polluted planet. The incredible journey of how that woman's family spread and grew to populate nearly every corner of the earth over tens of thousands of years is written in every drop of blood in our body. It is in our DNA.
A team of scientists working with National Geographic have undertaken the most grandly ambitious project in its history: charting the migration of human beings out of Africa using DNA to answer fundamental questions about the history of humanity. Where are we from? Why did our ancestors leave their homes? Where did they go? "The primary goal is really to quell this scientific curiosity, to acquire the knowledge about our history and our ancestors and how we got to populate the world the way we did today," says Dr Pierre Zalloua, population geneticist at the Lebanese American University in Beirut.
Zalloua's Beirut laboratory is among 11 research teams around the world that are led by the American population geneticist Dr Spencer Wells, a blond-haired, blue-eyed Viking of a man who is National Geographic's explorer-in-residence. As he likes to say, "The greatest story ever told is written in our DNA." Wells and his teams are criss-crossing the planet and collecting 100,000 DNA samples from indigenous people to find the answers to those questions. There's a complex science behind how every human being alive today is linked to our common female ancestor in the African savannah, or "Mitochondrial Eve".
The human genetic code is 99.9 per cent identical. The rest is what makes us different: eye colour or height, for example. Every time a couple has a baby, 99 per cent of the parents' DNA gets shuffled in the child. The Genographic Project traces the one per cent of the genome that is not shuffled: mitochondrial DNA (mtDNA), which is passed from mother to child, and the Y chromosome, which is inherited from father to son.
Every once in a while a random and harmless mutation can occur which is passed down to all of that person's descendants. But the rate of mitochondrial genetic mutation is so slow that it can be used as a clock to turn back to a period before the changes happened. Thousands of years later, finding that same mutation, or marker, in two people's DNA shows they share an ancestor. By comparing markers in different populations, scientists can create a timescale that gives them a sense of where and when these groups parted during migrations across the planet.
In the past, paleontologists have had to rely on physical remains to piece together our evolutionary history. But these genetic mutations allow scientists in a laboratory to work back through time until a period when our genetic material coalesced into one woman, Mitochondrial Eve, to whom we are linked in a long and unbroken chain of mothers. Our common male ancestor is "Y Chromosome Adam", who lived about 90,000 years ago in the Rift Valley in present-day Kenya or Tanzania. He probably looked like a modern San Bushman of the Kalahari, with a fold of skin over his forehead and spoke a language using clicking sounds.
All human beings on the planet today are traced back to Mitochondrial Eve and Y Chromosome Adam, but they were not the first human beings on the planet. The names do not refer to Adam and Eve in any religious way. "We refer to them only in the scientific sense," Zalloua says. The discrepancy in time between the pair lies in the fact that they are only the last common ancestors we can trace genetically. As the science advances and more information is gathered, earlier ancestors may be found and the time gap may be bridged. There were other women alive at the time of Mitochondrial Eve, but why her genes remain in us and not her contemporaries is down to random historical luck. She survived. The others did not.
To publicise the initiative and help satisfy the modish curiosity for genealogy - tracing ancestors is a hugely popular pastime in North America - the public has been encouraged to participate. For US$100 (Dh367), you can buy a do-it-yourself DNA kit that will reveal your own deep ancestry. The information will be entered into a database anonymously to help advance the researchers' understanding of our ancestors' migratory patterns. The money raised from the kits will be put into a fund to help indigenous communities around the world.
The project is non-profit and underwritten by the Waitt Family Foundation in America. IBM is providing the technology and is analysing the data in vast computer labs in New York. The major findings will be released in 2011 following scientific peer publication. All of it will be in the public domain. My family are Afghan. I was born in Kabul, as were my parents, grandparents, great-grandparents and so on. Little anthropological work has been done in Afghanistan, which has been invaded by dozens of civilisations for millennia. I was curious to know what the tests would reveal about myself.
After vigorously scraping the inside of my cheek with the provided swabs as instructed, I put them in a vial and mailed it to a laboratory in Texas. To protect privacy, the kits are anonymous. You are identified only by an alphanumeric code, which must be typed into a website to retrieve the results. On my father's side, we can trace our family back to the Mogul invasion in the 16th century. The founder of the Mogul empire, Babur Shah, gave his nephew, Lutfullah Beg, nearly half of Laghman province, probably as a reward for a military victory. We, his descendants, had lived there ever since in one long uninterrupted line. On my father's side, anyway.
On my mother's side, the history is a bit more obscure, other than the fact that they lived in Kabul province for many generations in a well-defended fortress to protect them from invasions. As a female, I can only trace my maternal line through mtDNA. Men can trace their ancestors more fully by tracing their maternal and paternal lines because they have both a Y chromosome and mtDNA. A month later I sat in front of my laptop, the mystery about to be unravelled by an unpromising series of 569 letters on a grey screen, data which allows scientists to reconstruct the migratory patterns of my genetic lineage.
It turns out I'm European. I'm in Haplogroup H, which comprises 40 to 60 per cent of the gene pool of most European populations. The results tell me that, about 15,000 years ago when the ice sheets of the last Ice Age retreated, humans moved north again from the Iberian Peninsula, Italy and the Balkans and into western Europe and began spreading. My earliest ancestors were part of Aurignacian culture. They used flint blades and weapons made from bone and ivory. They decorated their bodies with pierced shells and beads and produced the mysterious cave art in France's Chauvet-Pont-d'Arc.
"By far the most frequent mitochondrial lineage carried by these expanding groups was Haplogroup H," the results read. "Because of the population growth that quickly followed this expansion, your Haplogroup now dominates the European female landscape. In Rome and Athens, for example, the frequency of H is around 40 per cent of the entire population, and it exhibits similar frequencies throughout western Europe."
That got my interest. Could I be descended from Alexander the Great's Macedonian armies as they crossed the Hindu Kush in the third century BC? It is a tantalising and romantic thought. If they did, they have left their traces in my fair skin and blue eyes. But there are still many gaps in the migratory routes. How my family ended in Afghanistan is not known. We are not the first hominids to leave Africa. Indeed, earlier species, such as the Neanderthals, had been inhabiting Eurasia when our distant ancestors left 50,000 to 60,000 years ago.
The first groups of modern humans made the exodus out of Africa northwards in small families and clans, totalling no more than a couple of thousand. They moved a few kilometres up the land every generation, chasing game animals, roots and berries. Then 50,000 years ago they left Africa using two routes, either the Sinai Peninsula in modern Egypt (the path of my own ancestors) or the Bab el Mandeb in the Red Sea. The latter crossing was no more than a few kilometres wide, and the early humans would have easily crossed them into what is now the Middle East in small rafts.
"We believe they came through Bab el Mandeb and settled somewhere in Yemen and expanded slowly towards the peninsula and we believe another route that was used went a bit further north and coastal," says Zalloua. "These are the population that constituted most of the Levant now." Then, 45,000 years ago, they moved to Australia. A skull buried in Lake Mungo in Australia bears witness to this. But they left no other trace, because since then, the seas have risen, erasing the physical evidence.
Science is answering what archaeology cannot. The indigenous groups in Malaysia, Myanmar and nearly all Aborigines in Australia carry the mitochondrial DNA of these early ancestors, and the common markers in their genes have allowed the scientists to chart their migration. A second group spread across the rest of Asia and Europe, part of the second exodus out of Africa. A segment from this second migration went to central Asia. They scavenged roots and berries and shellfish in rock pools, and through the fertile grasslands they followed the game.
The ancient Asians crossed from Siberia to Alaska in the last Ice Age, via a land bridge between Asia and North America 15,000 to 20,000 years ago. Within 1,000 years they reached the tip of South America. Again, they moved very slowly, a few kilometres with each generation. Today they make up the native peoples of North and South America. Along the way our ancient ancestors sometimes came across the Neanderthals, but how these lesser-evolved beings interacted with modern humans is still a mystery. Did they look at each other with wonder? Hatred? Fear?
Over the course of many thousands of years, our ancestors' hair, eye and skin colour changed to adapt to the surroundings. To make up for Vitamin D deficiency as a result of the weak northern European sun, for example, the mutations to a few members' DNA that resulted in lighter hair, skin and eyes proved beneficial. These humans could absorb more Vitamin D and were better suited to survive; with better reproductive success, their genes spread and came to dominate the population.
But race has no meaning or value for the scientists. "It's not so much physical appearance that is interesting. What interests us is why people used certain routes and why they stayed in certain areas and not others," says Zalloua. "These are the questions we want to answer." The real focus is on indigenous populations of the world. Someone like me, an Afghan who left because of war and volatility, has been removed from her authentic genetic setting.
Indigenous people, of which there are only 350 million left, have, in a sense, purer DNA than the rest of us because they have never left the lands of their distant ancestors and can give a clearer picture of the migration routes. The Basques in Spain, certain ethnic groups in India and the native peoples of North and South America are being studied along with their culture and oral histories to piece together the puzzle.
The goal is to collect 100,000 DNA samples, and the research team is halfway there. In the Middle East, this has been a major headache. "People say, 'This guy's collecting DNA, why? To study heritage? Well, I know my heritage. I don't want to do this'," says Zalloua, who has collected 9,000 cheek swabs in the Middle East out of the 10,000 required. "People have been reluctant to participate with such a project, so it takes longer to explain. To do a study to really get the proper permit, collect samples in the Middle East, is like pulling teeth, and eight out of 10 times it takes years to get approval - if you get approval."
It is frustrating because precisely how the modern Middle East was populated is not known. "We really don't know much, because a lot of people had a nomadic lifestyle right until recently," he says. "We know they stayed here in the Arabian peninsula for a long time. We can safely say people have lived here for 10,000 years uninterrupted." So far, the research has made some fascinating discoveries about comparatively recent history in the Arab world. The Phoenicians ran an empire in the first millennium BC based in Lebanon, which grew wealthy from the trade routes they controlled through the Mediterranean basin. They ruled for almost 1,000 years until the conquest by Rome in the second century BC. Most of what was known about them has been lost or destroyed.
The research has shown that, surprisingly, as many as one in 17 men in the Mediterranean basin may have a Phoenician as a direct ancestor. The Lebanese are proud of their Phoenician ancestry, but it seems they share this history with their neighbours. A look at the legacy of the Crusades was also revealing. "During the Crusades, the crusaders came and more than 70 per cent stayed. These people came on foot and horse and took many months and never went back. Throughout the coast, wherever you see those crusader castles, you see them and find their descendants. We know, for instance, that the Romans did not leave any descendants because they did not mix with the population and neither did the Ottomans. Although they occupied the area for several hundred years, they didn't mix with the population."
For thousands of years human beings have been fighting each other and emphasising their physical, religious and ethnic differences, but this project perhaps reveals a simple, more elegant truth: we were all once African hunter-gatherers.