Ancient Humans

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 20^th 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.”