May 2, 2000
The Human Family Tree: 10 Adams and 18 Eves
Genetics: Gene Therapy
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Genetics: The Human Genome Project
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Tracing Human History Through Genetic Mutations
Follow the Lineages
Join a Discussion on DNA Research
By NICHOLAS WADE
he book of Genesis mentions three of
Adam and Eve's children: Cain, Abel and
But geneticists, by tracing the DNA
patterns found in people throughout the
world, have now identified lineages descended from 10 sons of a genetic Adam and 18
daughters of Eve.
The human genome is turning out to be a
rich new archive for historians and prehistorians, one whose range extends from recent times to the dawn of human existence.
Delvers in the DNA archive have recently
found evidence for a prehistoric human
migration from Western Asia to North
America; identified the people who seem
closest to the ancestral human population;
and given substantial weight to the whispers, long dismissed by historians, that
Thomas Jefferson 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, an 8,980-year-old skeleton
from which mitochondrial DNA was recently extracted.
The DNA turned out to match
that of Adrian Targett, a teacher in a Cheddar Village school, proving a genetic continuity that, despite numerous invasions, had
endured through nine millenniums.
Unlike the DNA test used in forensic
cases, which is designed to identify individuals, DNA analysis that seeks to reach back
in time usually focuses on lineages, not
individuals. From patterns in the DNA data,
biologists can often estimate the sizes of
ancient populations and even the approximate dates when one group of people split
Though DNA can bear on historical questions, often by acting as a long-range paternity test, its most spectacular use has been
in prehistory, where it has added a new
dimension to the bare framework provided
The most detailed human family tree so
far available is one constructed over many
years by Dr. Douglas C. Wallace and his
colleagues at the Emory University School
of Medicine in Atlanta. Dr. Wallace's tree is
based on mitochondrial DNA, tiny rings of
genetic material that are bequeathed only
by the egg cell and thus through the maternal line.
A counterpart tree for men, based
on analysis of the Y chromosome, has been
prepared by Dr. Peter A. Underhill and Dr.
Peter J. Oefner of Stanford University.
Population geneticists believe that the
ancestral human population was very small
-- a mere 2,000 breeding individuals,
according to a calculation published
last December. But the family tree
based on human mitochondrial DNA
does not trace back to the thousand
women in this ancestral population.
The tree is rooted in a single individual, the mitochondrial Eve, because
all the other lineages fell extinct.
The same is true of the Y chromosome tree, a consequence of the fact
that in each generation some men
will have no children, or only daughters, so the number of different Y
chromosomes may steadily diminish, even if the population stays the
This ancestral human population
lived somewhere in Africa, geneticists believe, and started to split up
some time after 144,000 years ago,
give or take 10,000 years, the inferred
time at which both the mitochondrial
and Y chromosome trees make their
Mitochondria, which live inside human cells but outside the nucleus,
escape the shuffling of genes that
occurs between generations and are
passed unchanged from mother to
In principle, all people
should have the same string of DNA
letters in their mitochondria. In
practice, mitochondrial DNA has
steadily accumulated changes over
the centuries because of copying errors and radiation damage.
Because women were steadily
spreading across the globe when
many of these changes occurred,
some changes are found only in particular regions and continents.
Wallace discovered that almost all
American Indians have mitochondria that belong to lineages he
named A, B, C and D. Europeans
belong to a different set of lineages,
which he designated H through K and
T through X. The split between the
two main branches in the European
tree suggests that modern humans
reached Europe 39,000 to 51,000
years ago, Dr. Wallace calculates, a
time that corresponds with the archaeological date of at least 35,000
In Asia there is an ancestral lineage known as M, with descendant
branches E, F and G as well as the A
through D lineages also found in the
In Africa there is a single main
lineage, known as L, which is divided
into three branches. L3, the youngest
branch, is common in East Africa
and 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 all
are branches of the trunk that stems
from the mitochondrial Eve.
The Y chromosome tree has not
yet been published by the Stanford
researchers, but in a book that came
out in March, "Genes, People and
Languages," 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 principal branches, Dr. Cavalli-Sforza reports.
Of these sons of Adam, the
first three (designated I, II and III)
are found almost exclusively in Africa. Son III's lineage migrated to
Asia and begat sons IV-X, who
spread through the rest of the world
-- to the Sea of Japan (son IV),
northern India (son V) and the South
Caspian (sons VI and IX).
Dr. Cavalli-Sforza believes these Y
chromosome lineages may be associated with the major language groups
of the world. The South Caspian population, for example, may have spoken Eurasian, the ancestral tongue
of Indo-European (to which English
belongs) and most of the continent's
other major language families.
Dr. Wallace, asked if his mitochondrial DNA lineages also corresponded to the world's major language groups, said he "tended to be
more cautious than Luca."
Dr. Wallace has recently been exploring the root of the mitochondrial
tree. In an article published in March
in The American Journal of Human
Genetics, he and colleagues identify
the Vasikela Kung of the northwestern Kalahari desert in southern Africa as the population that lies nearest to the root of the human mitochondrial DNA tree. Another population that seems almost equally old is
that of the Biaka pygmies of Central
Both peoples live in isolated
regions, which may be why their
mitochondrial DNA seems little
changed from that of the ancestral
population. "We are looking at the
beginning of what we would call
Homo sapiens," Dr. Wallace said.
One of the most vexed issues in
human prehistory is the timing and
number of migrations into the Americas. Dr. Joseph Greenberg, a linguist at Stanford University, has proposed three migrations, corresponding to the three language groups of
the Americas, known as Amerind,
Na-Dene and Eskimo-Aleut. Dr. Wallace's mitochondrial DNA data
broadly support this general thesis,
though the arrival of the Amerind-speakers seems more complex than
a single migration.
Of the A through D lineages found
in American Indians, A, C and D also
occur in Siberian peoples, suggesting
that their ancestors were the principal source of the Amerind-speakers'
migration. But the B lineage, though
it is found elsewhere in Asia, has not
turned up in Siberia, a hint that the B
people may have taken a sea route to
the Americas and then merged there
with their A- , C- and D-carrying
In 1998, Dr. Wallace and his colleagues discovered the X pattern, a
rare European lineage, among the
northern Native Americans such as
the Ojibwa and Sioux. At first they
assumed it came from intermarriage with modern Europeans. But
the American X lineage turned out to
be pre-Columbian and its owners
would have arrived in America either 15,000 or 30,000 years ago, depending on certain genetic assumptions.
The European X lineage seems to
have originated in Western Asia
around 40,000 years ago. Dr. Wallace
suggests a part of this group may
have made their way to America via
Siberia, even though no traces of the
X-lineage have yet turned up in eastern Asia. A trans-Atlantic route is a
When modern humans first started to leave Africa, about 50,000 years
ago by present reckoning, they probably consisted of small groups of
hunter-gatherers a few hundred
In their determined exploration of the world before them, they
must have overcome, with the primitive means at their disposal, the extreme rigors of climate, terrain and
perhaps the archaic human populations like the fearsome Neanderthals
who had preceded them out of Africa.
The biologist Edward O. Wilson, in
a recent interview with The Wall
Street Journal, mused that a new
basis for spiritual values might be
found -- not in the usual religious
sources but in what he sees as the
inspiring story of human origins and
"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 speaking both of deep history --
evolutionary, genetic history -- and
then, added on to that and interacting
with it, the cultural history recorded
for the past 10,000 years or so."
Many of the biologists who are
reconstructing the human past certainly believe their work has a value
that transcends genetics.
their lineage trees are based on genetic differences, most of these differences lie in the regions of DNA
that do not code for genes and have
no effect on the body.
"We are all
Africans at the Y chromosome level
and we are really all brothers," Dr.
Dr. Wallace remarked that since
he started working on mitochondrial
DNA in the late 1970's: "What I have
found astounding is that it clearly
shows we are all one human family.
The phylogeny in Africa goes back to
the origins of our species, but the
fingers of L3 are touching Europe
and Asia, saying that we are all
Whether or not genetic prehistory
is suitable material for a modern
origin myth, it is about to be made
available to a wider public.
month a company called Oxford Ancestors set up business with the offer
to tell customers which of the seven
daughters of Eve they are descended
from. (Almost all Europeans belong
to only seven of the nine mitochondrial lineages found in Europe). The
test (see www.oxfordancestors.com)
requires sending in a sample of cells
brushed from the inside of the cheek.
For a mere $180, anyone of European
ancestry can establish the start of a
genealogy far senior to Charlemagne's.
The company's founder is Dr. Bryan Sykes, a human geneticist at the
University of Oxford in England. On
the reasonable basis that the
founders of Dr. Wallace's mitochondrial DNA lineages were real women, Dr. Sykes gave them names and
sketched in details of their likely
dates and origin. Thus people found
to belong to haplogroup U will be told
they are descended from Ursula,
who lived about 45,000 years ago in
Northern Greece. Ancestor of the X's
is Xenia, who lived 25,000 years ago
in the Caucasus mountains.
As if fulfilling Dr. Wilson's suggestion, Dr. Sykes said he had "worked
out a mythological framework for
these seven women," in respect of
the arduous times in which they
must have lived and the triumph of
spreading their 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't think
this stuff should be confined to academics," he said.