I’m still trying to understand how my mother got to carry genes “found today at frequencies seldom greater than 20 percent in Europe, the Middle East, and Central Asia” to a tiny little city in Brazil. But the Middle-East part would explain much better my feisty nature than the Brazilian culture…
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YOUR GENETIC HISTORY
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Your Branch on the Human Family TreeYour DNA results identify you as belonging to a specific branch of the human family tree called haplogroup T. Haplogroup T contains the following subgroups: T, T2, T3, T4, T5.
The map above shows the direction that your maternal ancestors took as they set out from their original homeland in East Africa. While humans did travel many different paths during a journey that took tens of thousands of years, the lines above represent the dominant trends in this migration. Over time, the descendants of your ancestors ultimately made it into northeastern Europe, where most members of your haplogroup are found today. But before we can take you back in time and tell their stories, we must first understand how modern science makes this analysis possible. How DNA Can Help The string of 569 letters shown above is your mitochondrial sequence, with the letters A, C, T, and G representing the four nucleotides – the chemical building blocks of life – that make up your DNA. The numbers at the top of the page refer to the positions in your sequence where informative mutations have occurred in your ancestors, and tell us a great deal about the history of your genetic lineage. Here’s how it works. Every once in a while a mutation – a random, natural (and usually harmless) change – occurs in the sequence of your mitochondrial DNA. Think of it as a spelling mistake: one of the “letters” in your sequence may change from a C to a T, or from an A to a G. After one of these mutations occurs in a particular woman, she then passes it on to her daughters, and her daughters’ daughters, and so on. (Mothers also pass on their mitochondrial DNA to their sons, but the sons in turn do not pass it on.) Geneticists use these markers from people all over the world to construct one giant mitochondrial family tree. As you can imagine, the tree is very complex, but scientists can now determine both the age and geographic spread of each branch to reconstruct the prehistoric movements of our ancestors. By looking at the mutations that you carry, we can trace your lineage, ancestor by ancestor, to reveal the path they traveled as they moved out of Africa. Our story begins with your earliest ancestor. Who was she, where did she live, and what is her story? Your Ancestral Journey: What We Know Now We will now take you back through the stories of your distant ancestors and show how the movements of their descendants gave rise to your mitochondrial lineage. Each segment on the map above represents the migratory path of successive groups that eventually coalesced to form your branch of the tree. We start with your oldest ancestor, “Eve,” and walk forward to more recent times, showing at each step the line of your ancestors who lived up to that point. Mitochondrial Eve: The Mother of Us All Ancestral Line: “Mitochondrial Eve” Our story begins in Africa sometime between 150,000 and 170,000 years ago, with a woman whom anthropologists have nicknamed “Mitochondrial Eve.” She was awarded this mythic epithet in 1987 when population geneticists discovered that all people alive on the planet today can trace their maternal lineage back to her. But Mitochondrial Eve was not the first female human. Homo sapiens evolved in Africa around 200,000 years ago, and the first hominids – characterized by their unique bipedal stature – appeared nearly two million years before that. Though Homo sapiens have been around for about 200,000 years, about 150,000 to 170,000 years ago, a woman was born from whom we are all descended. This happened 30,000 years after Homo sapiens evolved in Africa. Eventually, for any number of reasons, all of the other lineages of people went extinct, and “Mitochondrial Eve” as we call her, was the only female who had descendants that are now living in the present day. We can all be traced back to that one woman, who lived about 170,000 years ago. Which begs the question, “So why Eve?” Simply put, Eve was a survivor. A maternal line can become extinct for a number of reasons. A woman may not have children, or she may bear only sons (who do not pass her mtDNA to the next generation). She may fall victim to a catastrophic event such as a volcanic eruption, flood, or famine, all of which have plagued humans since the dawn of our species. None of these extinction events happened to Eve’s line. It may have been simple luck, or it may have been something much more. It was around this same time that modern humans’ intellectual capacity underwent what author Jared Diamond coined the Great Leap Forward. Many anthropologists believe that the emergence of language gave us a huge advantage over other early human species. Improved tools and weapons, the ability to plan ahead and cooperate with one another, and an increased capacity to exploit resources in ways we hadn’t been able to earlier, all allowed modern humans to rapidly migrate to new territories, exploit new resources, and outcompete and replace other hominids, such as the Neandertals. It is difficult to pinpoint the chain of events that led to Eve’s unique success, but we can say with certainty that all of us trace our maternal lineage back to this one woman. The L Haplogroups: The Deepest Branches Ancestral line: “Eve” > L1/L0 Mitochondrial Eve represents the root of the human family tree. Her descendents, moving around within Africa, eventually split into two distinct groups, characterized by a different set of mutations their members carry. These groups are referred to as L0 and L1, and these individuals have the most divergent genetic sequences of anybody alive today, meaning they represent the deepest branches of the mitochondrial tree. Importantly, current genetic data indicates that indigenous people belonging to these groups are found exclusively in Africa. This means that, because all humans have a common female ancestor, “Eve,” and because the genetic data shows that Africans are the oldest groups on the planet, we know our species originated there. Haplogroups L1 and L0 likely originated in East Africa and then spread throughout the rest of the continent. Today, these lineages are found at highest frequencies in Africa’s indigenous populations, the hunter-gatherer groups who have maintained their ancestors’ culture, language, and customs for thousands of years. At some point, after these two groups had coexisted in Africa for a few thousand years, something important happened. The mitochondrial sequence of a woman in one of these groups, L1, mutated. A letter in her DNA changed, and because many of her descendants have survived to the present, this change has become a window into the past. The descendants of this woman, characterized by this signpost mutation, went on to form their own group, called L2. Because the ancestor of L2 was herself a member of L1, we can say something about the emergence of these important groups: Eve begat L1, and L1 begat L2. Now we’re starting to move down your ancestral line. Haplogroup L2: West Africa Ancestral line: “Eve” > L1/L0 > L2 L2 individuals are found in sub-Saharan Africa, and like their L1 predecessors, they also live in Central Africa and as far south as South Africa. But whereas L1/L0 individuals remained predominantly in eastern and southern Africa, your ancestors broke off into a different direction, which you can follow on the map above. L2 individuals are most predominant in West Africa, where they constitute the majority of female lineages. And because L2 individuals are found at high frequencies and widely distributed along western Africa, they represent one of the predominant lineages in African-Americans. Unfortunately, it is difficult to pinpoint where a specific L2 lineage might have arisen. For an African-American who is L2 – the likely result of West Africans being brought to America during the slave trade – it is difficult to say with certainty exactly where in Africa that lineage arose. Fortunately, collaborative sampling with indigenous groups is currently underway to help learn more about these types of questions and to possibly bridge the gap that was created during those transatlantic voyages hundreds of years ago. Haplogroup L3: Out of Africa Ancestral line: “Eve” > L1/L0 > L2 > L3 Your next signpost ancestor is the woman whose birth around 80,000 years ago began haplogroup L3. It is a similar story: an individual in L2 underwent a mutation to her mitochondrial DNA, which was passed onto her children. The children were successful, and their descendants ultimately broke away from the L2 clan, eventually separating into a new group called L3. You can see above that this has revealed another step in your ancestral line. While L3 individuals are found all over Africa, including the southern reaches of sub-Sahara, L3 is important for its movements north. You can follow this movement of the map above, seeing first the expansions of L1/L0, then L2, and followed by the northward migration of L3. Your L3 ancestors were significant because they are the first modern humans to have left Africa, representing the deepest branches of the tree found outside of that continent. Why would humans have first ventured out of the familiar African hunting grounds and into unexplored lands? It is likely that a fluctuation in climate may have provided the impetus for your ancestors’ exodus out of Africa. The African Ice Age was characterized by drought rather than by cold. Around 50,000 years ago the ice sheets of northern Europe began to melt, introducing a period of warmer temperatures and moister climate in Africa. Parts of the inhospitable Sahara briefly became habitable. As the drought-ridden desert changed to savanna, the animals your ancestors hunted expanded their range and began moving through the newly emerging green corridor of grasslands. Your nomadic ancestors followed the good weather and plentiful game northward across this Saharan Gateway, although the exact route they followed remains to be determined. Today, L3 individuals are found at high frequencies in populations across North Africa. From there, members of this group went in a few different directions. Some lineages within L3 testify to a distinct expansion event in the mid-Holocene that headed south, and are predominant in many Bantu groups found all over Africa. One group of individuals headed west and is primarily restricted to Atlantic western Africa, including the islands of Cabo Verde. Other L3 individuals, your ancestors, kept moving northward, eventually leaving the African continent completely. These people currently make up around ten percent of the Middle Eastern population, and gave rise to two important haplogroups that went on to populate the rest of the world. Haplogroup N: The Incubation Period Ancestral line: “Eve” > L1/L0 > L2 > L3 > N Your next signpost ancestor is the woman whose descendants formed haplogroup N. Haplogroup N comprises one of two groups that were created by the descendants of L3. The first of these groups, M, was the result of the first great wave of migration of modern humans to leave Africa. These people likely left the continent across the Horn of Africa near Ethiopia, and their descendants followed a coastal route eastward, eventually making it all the way to Australia and Polynesia. The second great wave, also of L3 individuals, moved north rather than east and left the African continent across the Sinai Peninsula, in present-day Egypt. Also faced with the harsh desert conditions of the Sahara, these people likely followed the Nile basin, which would have proved a reliable water and food supply in spite of the surrounding desert and its frequent sandstorms. Descendants of these migrants eventually formed haplogroup N. Early members of this group lived in the eastern Mediterranean region and western Asia, where they likely coexisted for a time with other hominids such as Neandertals. Excavations in Israel’s Kebara Cave (Mount Carmel) have unearthed Neandertal skeletons as recent as 60,000 years old, indicating that there was both geographic and temporal overlap of these two hominids. The ancient members of haplogroup N spawned many sublineages, which spread across much of the rest of the globe and are found throughout Asia, Europe, India, and the Americas. Haplogroup R: Spreading Out Ancestral line: “Eve” > L1/L0 > L2 > L3 > N > R After several thousand years in the Near East, individuals belonging to a new group called haplogroup R began to move out and explore the surrounding areas. Some moved south, migrating back into northern Africa. Others went west across Anatolia (present-day Turkey) and north across the Caucasus Mountains of Georgia and southern Russia. Still others headed east into the Middle East, and on to Central Asia. All of these individuals had one thing in common: they shared a female ancestor from the N clan, a recent descendant of the migration out of Africa. The story of haplogroup R is complicated, however, because these individuals can be found almost everywhere, and because their origin is quite ancient. In fact, the ancestor of haplogroup R lived relatively soon after humans moved out of Africa during the second wave, and her descendants undertook many of the same migrations as her own group, N. Because the two groups lived side by side for thousands of years, it is likely that the migrations radiating out from the Near East comprised individuals from both of these groups. They simply moved together, bringing their N and R lineages to the same places around the same times. The tapestry of genetic lines became quickly entangled, and geneticists are currently working to unravel the different stories of haplogroups N and R, since they are found in many of the same far-reaching places. Haplogroup T: Your Branch on the Tree Ancestral line: “Eve” > L1/L0 > L2 > L3 > N > R > T We finally arrive at your own clan, a group of individuals who descend from a woman in the R branch of the tree. The divergent genetic lineage that constitutes haplogroup T indicates that she lived sometime around 40,000 years ago. Haplogroup T has a very wide distribution, and is present as far east as the Indus Valley bordering India and Pakistan and as far south as the Arabian Peninsula. It is also common in eastern and northern Europe. Although your haplogroup was present during the early and middle Upper Paleolithic, T is largely considered one of the main genetic signatures of the Neolithic expansions. While groups of hunter-gatherers and subsistence fishermen had been occupying much of Eurasia for tens of thousands of years, around ten thousand years ago a group of modern humans living in the Fertile Crescent – present-day eastern Turkey and northern Syria – began domesticating the plants, nuts, and seeds they had been collecting. What resulted were the world’s first agriculturalists, and this new cultural era is typically referred to as the Neolithic. Groups of individuals able to support larger populations with this reliable food source began migrating out of the Middle East, bringing their new technology with them. By then, humans had already settled much of the surrounding areas, but this new agricultural technology proved too successful to ignore, and the surrounding groups quickly copied these new immigrants. Interestingly, DNA data indicate that while these new agriculturalists were incredibly successful at planting their technology in the surrounding groups, they were far less successful at planting their own genetic seed. Agriculture was quickly and widely adopted, but the lineages carried by these Neolithic expansions are found today at frequencies seldom greater than 20 percent in Europe, the Middle East, and Central Asia. Anthropology vs. Genealogy DNA markers require a long time to become informative. While mutations occur in every generation, it requires at least hundreds – normally thousands – of years for these markers to become windows back into the past, signposts on the human tree. Still, our own genetic sequences often reveal that we fall within a particular sub-branch, a smaller, more recent branch on the tree. While it may be difficult to say anything about the history of these sub-groups, they do reveal other people who are more closely related to us. It is a useful way to help bridge the anthropology of population genetics with the genealogy to which we are all accustomed. One of the ways you can bridge this gap is to compare your own genetic lineage to those of people living all over the world. Mitosearch.org is a database that allows you to compare both your genetic sequence as well as your surname to those of thousands of people who have already joined the database. This type of search is a valuable way of inferring population events that have occurred in more recent times (i.e., the past few hundred years). Looking Forward (Into the Past): Where Do We Go From Here? Although the arrow of your haplogroup currently ends across Western Eurasia, this isn’t the end of the journey for haplogroup T. This is where the genetic clues get murky and your DNA trail goes cold. Your initial results shown here are based upon the best information available todaybut this is just the beginning. A fundamental goal of the Genographic Project is to extend these arrows further toward the present day. To do this, Genographic has brought together ten renowned scientists and their teams from all over the world to study questions vital to our understanding of human history. By working together with indigenous peoples around the globe, we are learning more about these ancient migrations. Help Us Find More Clues! But there is another way that we will learn more about the past. By contributing your own results to the project, you will be allowed to participate anonymously in this ongoing research effort. This is important because it may contribute a great deal to our understanding of more recent human migrations. Click the yellow button below in the “Help Us Tell the Story” section of your results profile to learn more about this. It’s quick, easy, and anonymous, but will help us further refine our analyses. Don’t Be a Stranger Finally, keep checking these pages to follow along with the project and our latest findings; your results profile will be automatically updated to reflect any new information that may come to light based on the research. |
Sulamita Garcia 