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DNA Genealogy


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DNA genealogy involves the research of tracing the Y sex chromosome, which is passed intact from father to son. Humans are very much alike genetically, with most of the variation within, rather than between, ethnic groups. Finns, Sardinians and Basques, as well as Jews, are among groups with small founding populations that have highly distinctive genetic pedigrees. By contrast, most people of European origin are so genetically mixed that it’s impossible to tell German from Frenchman, Bosnian from Serb.

The tools of biotechnology have become so powerful that it’s now possible to deduce ancient human history from a drop of blood or a few shed skin cells. This molecular view of the past is already being employed to trace the cause of ailments such as cancer and heart disease. Most significantly for scientists studying past human life and culture, it offers the best insight yet into the mystery of how modern Homo sapiens arose out of archaic hominids who left Africa about 1.7 million years ago.

In coming years the whole course of early human history is going to become much clearer. In recent months two groups of geneticists have published sweeping chronicles of the peopling of Europe, one tracing maternal DNA lineages, the other, paternal. These findings portray the majority of European forebears arriving from the Middle East as hunter-gatherers 25,000 to 40,000 years ago. During the last Ice Age, these first Europeans fled south to Iberia, Ukraine and the Balkans. As the ice retreated, the Ice Age survivors spread out and flourished. The last major migration from the East 9,000 years ago brought agriculture and domestic animals but did not displace the earlier settlers, as some researchers had thought.

The European studies capitalize on a new ability to compare the migrations of males and females, which don’t always follow the same path through history. Researchers have been able to track women’s wanderings through mitochondria – tiny energy-producing bodies that cluster by the hundreds in human cells. Mitochondria have very odd DNA. They contain genetic material only from the maternal line, unlike the cell nucleus, which is a mix of DNA from both parents. This means that all children, male and female, carry copies of their mother’s mitochondrial DNA. This peculiarity gave geneticists a key tool for learning the movements of ancient populations. As mitochondrial DNA is passed along, tiny, harmless mutations occur. By comparing the mutations among people, it is possible to calculate how closely they’re related. By calculating the mutation rate, researchers can deduce how far back in time different groups split apart.

Scientists have been searching for human history in the genes since World War I, when two Polish immunologists discovered that different armies had very different proportions of various blood types. For example, Type B blood is more common in East Asians and Africans than it is in Europeans. Since blood type is hereditary, controlled by a single gene, a blood type can be used as a form of genealogy. Blood types were used to prove that the Romany, or Gypsies, originally came from the Indian subcontinent, not Europe.

In 1987 a group of researchers at the University of California-Berkeley, announced they had traced mitochondrial DNA back 200,000 years to the oldest female ancestor of living humans – an African woman whom they named Eve. There have been many Adams and many Eves. The genetic record reflects only those whose offspring survived and reproduced. The earliest forefather identified so far is 20,000 to 30,000 years younger than Eve. The bulk of the genetic data suggests that a small population of modern humans, as few as 10,000, left Africa 100,000 or so years ago, wandering into the Middle East and on to Asia and Europe.

There has been a dispute over just when humans first arrived in the New World. Archaeologists thought that people tramped across the Bering Land Bridge and through a gap in the glaciers about 14,000 years ago. Now the thinking is there were other migrations, one as early as 30,000 years ago. There are archaeology sites in Pennsylvania, Virginia and Chile that support this migration. The newest and most surprising discovery is a set of genetic markers found only in the Ojibwa and other tribes living near the Great Lakes; the markers are not found in any other native Americans or in Asia. It’s possible the DNA arrived with European colonists, but the strain is different enough from the existing European lineage that it must have left the Old World long before Columbus.

Research on the Y chromosome has been difficult and slow until 1995 when a geneticist at the University of Arizona identified key Y markers. He started to look for a cohanim (the priest caste) marker after he received a call from an Israeli physician who wondered if the different looking men who were reading the Torah could possibly be sons of Aaron, as the Bible said. The geneticist identified markers that are often shared by men who think they are cohanim. By comparison, he determined that the cohanim had a common male ancestor 84 to 130 generations ago – which includes the time of the exodus from Egypt and the original cohen, Aaron. Other researchers have used the cohanim markers to determine that the Lemba, a Bantu-speaking people in Southern Africa have Semitic roots. And recently results were published showing that although Palestinian and Jewish men may be political foes, they are so closely related as to be genetically indistinguishable.

The Y chromosome is beginning to produce other interesting tales. In 2000 a list of 87 new Y markers was published which sorts all of the world’s men into just 10 branches. Men’s lineages have much crisper divisions than women’s, probably because men moved into an area and killed or expelled the men already there. By contrast, women moved because they married into a new family or village. Generation after generation, daughters marry and move out, while sons stay put, making women’s DNA often more traveled than men’s.

Scientists are using molecular anthropology to seek the origins of disease. Some Eastern European roots have a gene that confers resistance to AIDS; women with Scottish ancestry are predisposed to one form of breast cancer; African-Americans are more apt to get sickle-cell anemia.

There is an oral tradition in Andy Carvin’s family that their family was cohanim, of the priest caste. After reading about research on the Y chromosome, he contacted Family Tree DNA and mailed a sample of his DNA, gathered by swabbing the inside of his cheek. He received a call that not only did his Y chromosome have the cohanim markers, but other markers matched those of another man in the database, indicating that they may have shared a forefather within the past 250 years. The two men arranged to meet and family photos showed resemblances between their fathers and other family members. Andy said that he felt like he was visiting one of his uncles.

Doug Mumma of California searched out strangers with his surname all over the world and paid to have their Y chromosomes tested. Many turned out to have no link to him, but he did locate several blood relatives in Germany.

Extracted from a longer article in U.S. News and World Report, January 29, 2001

June Pelo

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