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- From
Southern African Eve
Science magazine October 8, 1999 286: 229a
at http://www.shamema.com/evedna.htm
"Ann Gibbons
In the beginning, there was mitochondrial Eve--a woman who lived inAfrica between 100,000 and 200,000 years ago and was ancestral to allliving humans. Geneticists traced her identity by analyzing DNA passedexclusively from mother to daughter in the mitochondria, energy-producingorganelles in the cell. Scientists have been searching ever since for"Adam," the man whose Y chromosome was passed on to every living man andboy. Now two international teams have found the genetic trail leading toAdam--and it points to the same time and place where mitochondrial Evelived. Described this month at a symposium on human evolution at ColdSpring Harbor Laboratory in New York, the genetic trail is so clear thatit allows researchers to compare the migration patterns of men and womentens of thousands of years ago
Science Magazine - HUMAN EVOLUTION: Y Chromosome Shows That Adam Was anAfrican
Ann Gibbons
Science 1997 October 31; 278: 804-805.
http://www.sciencemag.org/cgi/content/summary/278/5339/804
The Human Family Tree: 10 Adams and 18 Eves
By NICHOLAS WADE
The New York Times: May 2, 2000
at http://www.shamema.com/adameve.htm
The book of Genesis mentions three of Adam and Eve's children: Cain, Abeland Seth.
But geneticists, by tracing the DNA patterns found in people throughoutthe world, have now identified lineages descended from 10 sons of agenetic Adam and 18 daughters of Eve.
The human genome is turning out to be a rich new archive for historiansand prehistorians, one whose range extends from recent times to the dawnof human existence.
Delvers in the DNA archive have recently found evidence for a prehistorichuman migration from Western Asia to North America; identified the peoplewho seem closest to the ancestral human population; and given substantialweight to the whispers, long dismissed by historians, that ThomasJefferson fathered a family with his slave Sally Hemings.
A new history of Britain and Ireland by Norman Davies, "The Isles,"(Oxford University Press) begins with an account of Cheddar man, an8,980-year-old skeleton from which mitochondrial DNA was recentlyextracted.
The DNA turned out to match that of Adrian Targett, a teacher in aCheddar Village school, proving a genetic continuity that, despitenumerous invasions, had endured through nine millenniums.
Unlike the DNA test used in forensic cases, which is designed to identifyindividuals, DNA analysis that seeks to reach back in time usuallyfocuses on lineages, not individuals. From patterns in the DNA data,biologists can often estimate the sizes of ancient populations and eventhe approximate dates when one group of people split from another.
Though DNA can bear on historical questions, often by acting as along-range paternity test, its most spectacular use has been inprehistory, where it has added a new dimension to the bare frameworkprovided by archaeology.
The most detailed human family tree so far available is one constructedover many years by Dr. Douglas C. Wallace and his colleagues at the EmoryUniversity School of Medicine in Atlanta. Dr. Wallace's tree is based onmitochondrial DNA, tiny rings of genetic material that are bequeathedonly by the egg cell and thus through the maternal line.
A counterpart tree for men, based on analysis of the Y chromosome, hasbeen prepared by Dr. Peter A. Underhill and Dr. Peter J. Oefner ofStanford University.
Population geneticists believe that the ancestral human population wasvery small -- a mere 2,000 breeding individuals, according to acalculation published last December. But the family tree based on humanmitochondrial DNA does not trace back to the thousand women in thisancestral population. The tree is rooted in a single individual, themitochondrial Eve, because all the other lineages fell extinct.
The same is true of the Y chromosome tree, a consequence of the fact thatin each generation some men will have no children, or only daughters, sothe number of different Y chromosomes may steadily diminish, even if thepopulation stays the same size.
This ancestral human population lived somewhere in Africa, geneticistsbelieve, and started to split up some time after 144,000 years ago, giveor take 10,000 years, the inferred time at which both the mitochondrialand Y chromosome trees make their first branches.
Mitochondria, which live inside human cells but outside the nucleus,escape the shuffling of genes that occurs between generations and arepassed unchanged from mother to children.
In principle, all people should have the same string of DNA letters intheir mitochondria. In practice, mitochondrial DNA has steadilyaccumulated changes over the centuries because of copying errors andradiation damage.
Because women were steadily spreading across the globe when many of thesechanges occurred, some changes are found only in particular regions andcontinents.
Dr. Wallace discovered that almost all American Indians have mitochondriathat belong to lineages he named A, B, C and D. Europeans belong to adifferent set of lineages, which he designated H through K and T throughX. The split between the two main branches in the European tree suggeststhat modern humans reached Europe 39,000 to 51,000 years ago, Dr. Wallacecalculates, a time that corresponds with the archaeological date of atleast 35,000 years ago.
In Asia there is an ancestral lineage known as M, with descendantbranches E, F and G as well as the A through D lineages also found in theAmericas.
In Africa there is a single main lineage, known as L, which is dividedinto three branches. L3, the youngest branch, is common in East Africaand is believed to be the source of both the Asian and European lineages.
Dr. Wallace's mitochondrial DNA lineages are known technically as"haplogroups" but more colloquially as "daughters of Eve," because allare branches of the trunk that stems from the mitochondrial Eve.
The Y chromosome tree has not yet been published by the Stanfordresearchers, but in a book that came out in March, "Genes, People andLanguages," a colleague at the university, Dr. Luca Cavalli-Sforza,sketched a preview of the findings.
The tree is rooted in a single Y chromosomal Adam, and has 10 principalbranches, Dr. Cavalli-Sforza reports.
Of these sons of Adam, the first three (designated I, II and III) arefound almost exclusively in Africa. Son III's lineage migrated to Asiaand begat sons IV-X, who spread through the rest of the world -- to theSea of Japan (son IV), northern India (son V) and the South Caspian (sonsVI and IX).
Dr. Cavalli-Sforza believes these Y chromosome lineages may be associatedwith the major language groups of the world. The South Caspianpopulation, for example, may have spoken Eurasian, the ancestral tongueof Indo-European (to which English belongs) and most of the continent'sother major language families.
But Dr. Wallace, asked if his mitochondrial DNA lineages alsocorresponded to the world's major language groups, said he "tended to bemore cautious than Luca."
Dr. Wallace has recently been exploring the root of the mitochondrialtree. In an article published in March in The American Journal of HumanGenetics, he and colleagues identify the Vasikela Kung of thenorthwestern Kalahari desert in southern Africa as the population thatlies nearest to the root of the human mitochondrial DNA tree. Anotherpopulation that seems almost equally old is that of the Biaka pygmies ofCentral Africa.
Both peoples live in isolated regions, which may be why theirmitochondrial DNA seems little changed from that of the ancestralpopulation. "We are looking at the beginning of what we would call Homosapiens," Dr. Wallace said.
One of the most vexed issues in human prehistory is the timing and numberof migrations into the Americas. Dr. Joseph Greenberg, a linguist atStanford University, has proposed three migrations, corresponding to thethree language groups of the Americas, known as Amerind, Na-Dene andEskimo-Aleut. Dr. Wallace's mitochondrial DNA data broadly support thisgeneral thesis, though the arrival of the Amerind-speakers seems morecomplex than a single migration.
Of the A through D lineages found in American Indians, A, C and D alsooccur in Siberian peoples, suggesting that their ancestors were theprincipal source of the Amerind-speakers' migration. But the B lineage,though it is found elsewhere in Asia, has not turned up in Siberia, ahint that the B people may have taken a sea route to the Americas andthen merged there with their A- , C- and D-carrying cousins.
In 1998, Dr. Wallace and his colleagues discovered the X pattern, a rareEuropean lineage, among the northern Native Americans such as the Ojibwaand Sioux. At first they assumed it came from intermarriage with modernEuropeans. But the American X lineage turned out to be pre-Columbian andits owners would have arrived in America either 15,000 or 30,000 yearsago, depending on certain genetic assumptions.
The European X lineage seems to have originated in Western Asia around40,000 years ago. Dr. Wallace suggests a part of this group may have madetheir way to America via Siberia, even though no traces of the X-lineagehave yet turned up in eastern Asia. A trans-Atlantic route is a possiblealternative.
When modern humans first started to leave Africa, about 50,000 years agoby present reckoning, they probably consisted of small groups ofhunter-gatherers a few hundred strong.
In their determined exploration of the world before them, they must haveovercome, with the primitive means at their disposal, the extreme rigorsof climate, terrain and perhaps the archaic human populations like thefearsome Neanderthals who had preceded them out of Africa.
The biologist Edward O. Wilson, in a recent interview with The WallStreet Journal, mused that a new basis for spiritual values might befound -- not in the usual religious sources but in what he sees as theinspiring story of human origins and history.
"We need to create a new epic based on the origins of humanity," he said,adding: "Homo sapiens have had one hell of a history! And I am speakingboth of deep history -- evolutionary, genetic history -- and then, addedon to that and interacting with it, the cultural history recorded for thepast 10,000 years or so."
Many of the biologists who are reconstructing the human past certainlybelieve their work has a value that transcends genetics.
Although their lineage trees are based on genetic differences, most ofthese differences lie in the regions of DNA that do not code for genesand have no effect on the body.
"We are all Africans at the Y chromosome level and we are really allbrothers," Dr. Underhill said.
Dr. Wallace remarked that since he started working on mitochondrial DNAin the late 1970's: "What I have found astounding is that it clearlyshows we are all one human family. The phylogeny in Africa goes back tothe origins of our species, but the fingers of L3 are touching Europe andAsia, saying that we are all closely related."
Whether or not genetic prehistory is suitable material for a modernorigin myth, it is about to be made available to a wider public.
Last month a company called Oxford Ancestors set up business with theoffer to tell customers which of the seven daughters of Eve they aredescended from. (Almost all Europeans belong to only seven of the ninemitochondrial lineages found in Europe). The test (seewww.oxfordancestors.com) requires sending in a sample of cells brushedfrom the inside of the cheek. For a mere $180, anyone of Europeanancestry can establish the start of a genealogy far senior toCharlemagne's.
The company's founder is Dr. Bryan Sykes, a human geneticist at theUniversity of Oxford in England. On the reasonable basis that thefounders of Dr. Wallace's mitochondrial DNA lineages were real women, Dr.Sykes gave them names and sketched in details of their likely dates andorigin. Thus people found to belong to haplogroup U will be told they aredescended from Ursula, who lived about 45,000 years ago in NorthernGreece. Ancestor of the X's is Xenia, who lived 25,000 years ago in theCaucasus mountains.
As if fulfilling Dr. Wilson's suggestion, Dr. Sykes said he had "workedout a mythological framework for these seven women," in respect of thearduous times in which they must have lived and the triumph of spreadingtheir mitochondrial DNA to almost all the inhabitants of Europe.
He is now working on tests to identify other lineages around the world,including 14 in Africa, and 16 in Eurasia and the Americas. "I don'tthink this stuff should be confined to academics," he said.
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