REFERENCE
Rasmussen et al. “An Aboriginal Australian Genome Reveals Separate
Human Dispersals into Asia.” Science (2011) 334 pgs 94 – 98.
Two theories exist to explain the
ancestry of Aboriginal Australians (Figure 5.1). The first, called the Single-Dispersal model,
claims that Africans split from Eurasians, which then became Europeans and
Asians, which led to Aboriginal Australians.
Unfortunately, the split between Europeans and Asians is believed to
have occurred 17,000 to 43,000 years ago but archeological data suggests that
anatomically correct humans were in Australian around 50,000 years ago.
The
second model, called the Multi-Dispersal model, suggests that an earlier and
perhaps independent dispersal occurred before the split between Africans and
Eurasians.
To
determine which model is correct, Rasmussen et al. sequenced the genomic and
mitochondrial DNA from the hair of an early 20th century Aboriginal
male and detailed their findings in the most recent issue of Science.
They found that Aboriginal Australians shared
significantly more derived alleles with Asians (Cambodian, Japanese, Han and Dai)
than Europeans (French) and that Europeans shared more derived alleles with Asians
than Aboriginal Australians.
The
authors went on to sequence three Han Chinese genomes and used this data to support
their conclusions that Aboriginal Australians split from African populations
before Eurasians differentiated into Europeans and Asians, thus supporting a
Mutliple-Dispersonal model. Fitting well
with archeological data, it was concluded that this split occurred 62,000 to
75,000 years ago while the European/Asian split was 25,000 to 38,000 years ago.
Rasmussen
et al. concede that making one Aboriginal Australian DNA sample representative
of an entire population may not be entirely fair. However, if true,
Aboriginal Australians are the direct descendants of the first humans in Australia
and “…likely have one of the oldest continuous population histories outside of
sub-Saharan Africa today.”
