6. History prior to the last Ice Age
Internet resources about the uses of DNA testing and the development of fields dubbed "genetic anthropology",
"population genetics" and "migration genetics" are proliferating rapidly. This page lists the best webpages to read if you
want to get to grips with the wider impact of genetic studies on human history.
DNA testing and genetic analysis is a key tool in investigating man's ancient origins, in particular the
competing
out of Africa and
multiregional theories. Broadly, the 'out of Africa'
theory suggests that
homo sapiens populated the rest of the world from Africa from a single starting point while
the multiregional thesis suggests the human population arose in several places on the planet independently.
One startling new idea generated by comparing data from maternally- and paternally-inherited DNA
is that our male and female ancestors didn't always travel together and that women
seem to have dispersed their DNA more widely than the warrior men did.
The second is that all Northern Europeans could be descended from between just
50-1,000 Stone Age hunter-gatherers
who survived the last Ice Age. One theory is that the population expanded from a small enclave of foragers who
retreated south around 20,000 years ago to an area in the Balkans or Spain to escape the spread of the glaciers.
Such genetic data fits in surprisingly well with archaeological clues.
The findings suggest northern Europeans diverged from their African roots as recently as 27,000-53,000 years ago and were then
subjected to a genetic bottleneck caused by the climate changes wreaked by the last Ice Age.
The study measured the amount of shuffling of human DNA that has occurred over time by comparing Northern European DNA
with the Nigerian population. While similar in many places, the European samples show large clumps of unshuffled genetic
material, suggesting a recent breeding bottleneck. (The study is reported in the 10th May 2001 issue of the
journal
Nature.)
There are many good pre-history resources on the web if you want to look into this more deeply.
BBC Online has an
Apeman portal
that ties in with a recent tv series. The University of California at Santa Barbara has a fascinating
timeline of evolution with shockwave
that allows you to rotate the view of different primate skulls at the key stages of human evolution.
A good educational and promotional website in South Africa is
Welcome to the Cradle of Humankind which has
details of the World Heritage Site in the provinces of Gauteng and the North West
where many of the oldest human remains have been found. Look for the neat shockwave presentation of evolving man!
The latest information about how DNA analysis is changing our view of our more distant origins is laid out
in a special issue of
Science magazine about evolutionary genetics and migrations.
(Unfortunately it can only be viewed by subscribers.)
Research by scientists from
eight countries has concluded that the most recent ancestor of all males living today was a man who lived in
Africa around 59,000 years ago. The results came after drawing up a genetic family tree of mankind by
studying variations in the Y-chromosome of 1,062 men in 22 geographical areas including Pakistan, India,
Cambodia, Laos, Australia, New Guinea, America, Mali, Sudan, Ethiopia and Japan.
Some modern-day men living in what is now Sudan, Ethiopia and southern Africa are believed to be the closest
living descendants of the first humans left Africa 35,000-89,000 years ago. It also concluded
that the common matrilineal origin was some 80,000 years earlier, circa 140,000 BP (before the present).
This suggests all modern humans stem from individuals that left Africa in the past 200,000 years,
replacing all indigenous people they encountered. It is, however, still possible that some of our nuclear DNA
comes from archaic humans who were not part of that more recent migration out of Africa and that living humans are
descended from several archaic Old World populations including Neandertals.
A second study investigated
more than 12,000 men across Asia and
failed to find a single example where a known mutation associated with the African population was missing. it concluded
that the 'Out of Africa' theory is correct in saying that the extant populations in Asia were wiped out by the wave
of humans from Africa. An earlier study of
Chinese men
from 28 population groups came to the same conclusion.
Another study has concluded that more than 95% of European men alive today are descended from
10 ancient groups of forefathers.
It concluded that 80% of European men inherited their Y-chromosomes from primitive hunter-gatherers who lived up to
40,000 years ago. The remaining 20% of male ancestors are likely to have been migrants who arrived in Europe from the
Near East about 10,000 years ago bringing with them farming technology.
Professor Bryan Sykes from Oxford University has a slightly different theory.
He believes that only as 15-20% of modern Europeans can be linked by their mtDNA to Middle Eastern populations
that not many farmers left the Middle East to resettle in Europe; instead, Europeans
copied their way of life.
A recent University of Leicester study headed by Mark Jobling found that modern Y-chromosomal
diversity in Europe is clinal (i.e. changes in it are layered across the continent in a regular and gradual way)
and that this picture is influenced primarily by geography, rather than by language.
Previous Y-chromosome studies had revealed clinal patterns of genetic diversity within Europe
which were interpreted as a Neolithic-era diffusion illustrating the spread of agriculture.
mtDNA studies had, however, traced many founding lineages back to the Paleolithic era and had not shown a
similarly strong clinal variation. In this broader Y-chromosome study the pan-European team analysed
11 human Y-chromosomal biallelic polymorphisms defining 10 haplogroups in a sample
of 3,616 individuals from 47 European and circum-European populations. Five of six haplogroups analysed revealed
clinal distributions while clines for two haplogroups, representing 45% of the chromosomes, were found continent-wide.
These findings are consistent with the demic diffusion hypothesis.
Clines for three other haplogroups were found to each have different foci; more regionally restricted
they are likely to reflect distinct population movements, including one from north of the Black Sea area.
The study concludes that geography is the prime factor in the shaping of the patterns of haplogoup variation which
nonetheless indicate an expansion from the Near East but also suggest that the demographic history of
Europe has been complex and influenced by other major population movements.
(The study was reported in the
American Journal of Human Genetics in December 2000.)
A
Swedish study
has reached a broadly similar conclusion within a longer timeframe after a study of the complete
mitochondrial genomes of 53 people from around the world.
They date the common female ancestor 171,000 ± 50,000
years ago with a
genetic divide
50,000 ± 27,500 years ago when an exodus from Africa took place.
The research also suggests that just 40,000 years ago there could have been as few as 40,000 humans on the planet.
Professor Sykes from
Oxford University brings the date forward a bit and
captured wide press attention in 2000 with the claim that everyone in Europe is descended from just
seven women
who arrived on the continent at different times during the last 45,000 years.
The data was taken from an analysis of 6,000 mtDNA samples and found that the seven "ancestral mothers"
have strong links to one of three groups in Africa today. Virtually all European populations have
representatives of all seven "mothers", though the Basques, traditionally seen as a separate group,
thus far appear to have only those from six. ABC News has an
interactive map of the
7 daughters if you press the "Inter Active Click" button.
Prof. Sykes's work built upon an earlier study dubbed 'The 18 Daughters of Eve' by Dr. Douglas C. Wallace at
the
Centre for Molecular Medicine, Emory University, Atlanta, and colleagues.
In the March 2000 edition of The American Journal of Human Genetics, he identified the
Vasikela Kung tribe of the northwestern Kalahari desert in southern Africa as the population that lies nearest
to the root of the human mtDNA tree. Another population that seems almost equally old is that of the Biaka pygmies of Central Africa.
A
NY Times article in May 2000
The Human Family Tree: 10 Adams and 18 Eves has a clear explanation of this research
[NB: you will have to take a free registration to access the NYT site]. Check out also its
lineage charts for both men and women and
the
map showing migration routes.
This can be compared with the earlier
Emory University version [.pdf format].
The Emory website also has a
map of human mitochondrial DNA (also
in
.pdf format) while the Oxford Ancestors website
has a more representational version showing
the geographic origins
of the different mtDNA progenitors, or daughters of Eve, and how they link together.
DNA evidence has been used to demonstrate the
evolutionary fate of the Neanderthals who were replaced in Europe
about 30,000 and 40,000 years ago by modern humans. The magazine
Nature has also reported the
extraction and sequencing of DNA from
29,000-year-old bone material of a Neanderthal found in the northern Caucasus.
This study also provided evidence that there had been
little gene flow between Neanderthals and modern humans.
Recent research notes the
difference in the diets
of early humans and neanderthals.
There are, however, both DNA and fossil challenges to the Out of Africa theory (which posits
that all living people are descended from a group of fully modern Homo sapiens who left their African homeland
about 100,000 to 150,000 years ago). Analysis of the oldest DNA ever taken from skeletal remains, from the
60,000 year-old "Mungo Man"
in Australia, show him to have a genetic lineage that is both older and distinct from the African line.
Australian aborigines would thus descend from members of two migrations about forty millenia apart rather than a single one.
The fossil evidence against the Out of Africa theory comes from two skulls found in
Georgia that are thought to be
1.7 million years old. If true they would be the oldest human remains found outside of Africa and would suggest
that early humans moved from that continent hundreds of thousands of years earlier than previously acepted.
Our understanding of mankind's earliest origins is appears to be becoming more complex rather than simpler. The discovery of a
new hominid potentially
3.5 million years old suggests that
there were several human-like species that were well adapted to life in different environments alive at the same time
rather than a single species.
Recent discoveries in Africa and France have
put the date of the first hominid back to almost 6 million years BP.
At the same time, DNA analysis is showing that the
genetic differences between man and chimpanzees
are less than previously thought.
More broadly,
new dating techniques may
require our evolution timelines to be lengthened.
Finally, it's not only human DNA which is helping scientists track colonisation and migration routes.
Recent research shows that
marsupials,
pouched mammals found mainly in Australia like the kangaroo and kaola, are
more closely related to most other mammals, including humans, than to monotremes like the duck-billed platypus
and the spiny anteater. It confirms other research on fossilised mammal teeth
which suggested that many millions of years ago monotremes evolved separately in the Southern Hemisphere
while marsupials and placental mammals shared a more recent ancestor in the Northern Hemisphere. The new findings run
counter to evidence from mtDNA analysis that links marsupials and monotremes together, thus opening up the possibility that mtDNA
analysis of human populations, which underpins the 'Out of Africa' theory for humanity, may not be as robust as thought.
[
Abstract]
An mtDNA examination of
406 goats in
44 countries suggests that they were the favoured
domesticated animal of Neolithic farmers as
they moved across Europe and the Near East.
In Asia, examination of one species of lizard found on various Pacific islands has convinced an Australain
evolutionary biologist that they were probably carried across the oceans by
migrating humans.
DNA studies have shown too that horses were domesticated simultaneously in many parts of the world, not just one,
while all hamsters link back to a single progenitor from Syria only 70-odd years ago.
DNA analysis is also a vital tool in plant science, for example being used to show that modern apples are
not hybrids of some of the dozens of
malus species worldwide but direct descendents of an apple
found in the remoter parts of Kazakhstan in central Asia on the fringes of the Tien Shan mountain range.
Indo-European mummies in well-preserved wooden tombs from the edge of the Taklamakan desert demonstrate
how traders could have brought our apples' ancestors to Europe via the Black Sea.
Recent detective work on pathogens has also shown that our assumptions about the cause of the
Irish potato famine in the 1840s
needs to be re-examined.
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All corrections & updates should be sent to the page maintainer: Chris Pomery
Last updated: 1st August 2001. Pages launched: 2nd March 2001.
