Australia can seem like the Land That Time Forgot. Australian marsupials were largely isolated from competition with placental mammals from other continents. (Although humans seem to have done in a lot of the megafauna when they arrived.) And many discussions of human prehistory assume that outside contact had little effect on Australia from the time of first settlement, before forty thousand years ago, and the English settlement of 1788. Populations just rose and fell with changes in climate and home-grown innovations in technology.
But there have always been hints that the story was more complicated. Some of the evidence comes from language distributions. The distribution of Australian languages is extremely lopsided. There are a lot of language families in and around the northern peninsula of Arnhemland. Then just one family, Pama-Nyungan, (distantly related to some or all of the others) covers about 80% of the continent.
This sort of distribution is seen with other language families, where it looks like the signature of population spreads. For example, three of four major branches of the Austronesian language family are found only on Taiwan. The fourth branch, Malayo-Polynesian, spans the world from Madagascar, to island Southeast Asia, to Easter Island. The explanation, supported by many lines of evidence, and almost universally accepted, is that Proto-Austronesian first diverged into separate languages on Taiwan. One bunch of Austronesian speakers then sailed to the Philippines, and thence to farther isles, their languages diverging along the way … and the rest is history (actually prehistory). A similar argument roots the Bantu expansion in the Nigeria-Cameroon border area.
So it looks like there was a similar expansion in Australia. Language change is hard to date, but it’s very hard to believe the expansion happened forty thousand years ago. There is other evidence suggesting a recent date. Some time before 2000 BCE, a new archeological culture, the Small Tool Tradition, swept over Australia. At the same time, natives began exploiting a far wider range of habitats and food sources than previously. And – strikingly – a new animal makes its appearance – the dingo, which must have been introduced from overseas. All of this makes it look like some outside contact, jump-started a continent-scale cultural expansion with new technology, and maybe new forms of social organization.
Just published work on Australian genetics suggests a complicated picture. Northeastern and southwestern Australia, separated by the interior desert, are also strongly genetically differentiated, reflecting a split probably going back sometime between 32 and 10 thousand years ago, i.e. well after initial colonization, but well before the spread of the Small Tool Tradition. But there is also evidence that the last 10 thousand years saw a population expansion in the northeast, a population bottleneck in the southwest, and some gene flow between the two. A scenario that fits the data would be Pama-Nyungan speakers expanding in northeast, and then some northeasterners migrating to the southwest, spreading their language and culture, but not arriving in such large numbers as to replace local populations.
On the other hand a story about gene flow from India (or an India-like population) that I blogged about last year may not hold up.
We can expect that the picture will grow clearer as more data accumulate.