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Out of Africa
Meet some Africans
Not from Africa at all!
Thailand:
Mani
Malaysia:
Semang
Andaman Islands: Andamanese
Fiji: Fijians
Hominin Species
0.2 million years ago
2.4 million years ago
H. erectus & H. neanderthalensis
• H. erectus lived from about 1.8 MYA to 70,000 years ago. H. erectus was the first human
ancestor to walk truly upright.
• After Homo erectus migrated out of Africa the different populations became reproductively
isolated, evolving independently, and in some cases like the Neanderthals, into separate
species H. neanderthalensis lived from about 350,000 to as recent as 30,000 years ago.
• The prevailing view is that no gene flow occurred between H. neanderthalensis and H.
sapiens, and, therefore, the two were separate species.
H. sapiens
•
Studies of contemporary DNA, especially mitochondrial DNA (mtDNA)
reveal that humans are astonishingly homogeneous, with relatively little
genetic variation.
•
The highest level of genetic variation in mtDNA occurs in African
populations. This implies that Homo sapiens arose first in Africa and has
therefore had a longer period of time to accumulate genetic diversity.
•
Using the genetic distance between African populations and others as a
measure of time, it has been calculated that Homo sapiens arose between
100,000 and 400,000 years ago in Africa.
•
The low amount of genetic variation in modern human populations suggests
that our origins may reflect a relatively small founding population for Homo
sapiens. Analysis of mtDNA supports the view that a small population of
Homo sapiens, numbering perhaps only 10,000 to 50,000 people, left Africa
somewhere between 50,000 and 100,000 years ago.
H. sapiens
Mitochondrial Eve
•
Because the rate of mitochondrial genetic mutation is slow, it can be used as a clock to turn back
time to a period before the mutations had crept in. When mitochondrial DNA from certain
populations in Africa are sampled, they can be compared with European mitochondrial DNA. The
mutation difference between the two populations can then be compared, and a 'clock' can be
produced, enabling the rate of mutation in mitochondria to be established. This produces a timescale which indicates when modern Europeans first left Africa.
•
The genetic survey that produced the whole Mitochondrial Eve scenario sampled genes from
people all over the planet. When mitochondrial DNA was compared, the survey discovered a
startling result. Fundamental similarities in mitochondrial DNA in living humans suggested that we
all contain genetic material from a single woman who was living in Africa around 200,000 years
ago.
•
Research at Oxford University and elsewhere over many years has shown that all of our maternal
lines are connected at some time in the past and that these connections can be traced by reading
mtDNA. One striking finding was that people tended to cluster into a small number of groups,
which could be defined by the precise sequence of their mtDNA. In native Europeans, for
example, there were seven such groups, among Native Americans there were four, among
Japanese people there were nine, and so on. Each of these groups, by an astounding yet
inescapable logic, traced back to just one woman, the common maternal ancestor of everyone in
her group, or clan.
•
There are about 36 mtDNA ancestral mothers world-wide.