2100 BCE. Australia can seem like the Land That Time Forgot. Australian marsupials were largely isolated from competition with placental mammals from other continents. 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 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, and is generally taken to be a signature of a demic expansion. 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 language 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 to the Nigeria-Cameroon border area.
So it looks like there was also a demic 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. A little over 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, presumably in Arnhemland, jump-started a continent-sized demic expansion with new technology, and maybe new forms of social organization. And (once again) recent genetic work supports the linguistic story. Irina Pugach, with other researchers, has found that Australian aborigines are genetically similar to New Guinea natives, with evidence for a split about 36,000 year ago. But the team also finds evidence for a substantial gene flow from India (or an India-like population) in some aboriginal populations going back about 2100 BCE. (Here’s a popular account.)