In the video below Willerslev describes how subtle the observations are. “A tiny genetic signature, like two men entering a village... they have a little bit of sex in that village and then they disappear,” he said. “It reminds me of a situation like the British coming to India where a very few people have an enormous impact.”
On the other hand, Willerslev confirmed that for most of the period of human occupation Australia has been almost entirely isolated, with only limited population exchange with New Guinea until very recently.
The fact is intriguing, raising questions about why the great migrations that populated islands as distant from Southeast Asia as Polynesia and Madagascar seem to have left Australia untouched.
It also has significance outside purely scientific debates. At one time it was thought Australia was settled by successive waves of people, each largely displacing previous inhabitants. Even before this paper, evidence overwhelmingly refuting the theory had emerged, but this did not stop an Australian Senator referring to the idea in order to oppose constitutional recognition of Australian Aborigines.
Past attempts to study the genetics of indigenous populations have often been done very insensitively, with questions over informed consent and subsequent protests from the affected peoples. Willerslev attempted to address this, consulting with leaders of the communities involved, some of whom became co-authors on the paper.
The paper is accompanied by two others that also use the genomes of understudied populations to explain the exodus from Africa. One finds that at least 200,000 years ago, while still geographically within Africa, the population that became our ancestors began to diverge. At this point the rate of genetic mutations increased by 5 percent among the ancestors of non-African populations compared to those that stayed in Africa, possibly as a result of having children earlier.
The third paper concludes that at least 2 percent of the genome of modern Papuans comes from a people who became temporarily separated from the rest of humanity at a much earlier point.