Australia’s indigenous languages contain a mystery. One language family dominates: more than three-quarters of the country’s close to 400 indigenous languages belong to the Pama-Nyungan family. At some point, this language family swept across the country—it’s spoken in 90 per cent of the continent—but when did that happen, and why?

New Zealand and United States researchers adapted computer models developed to track virus outbreaks, and used them to trace the language’s family tree by mapping the history of cognates, or similar words in related languages. The study, published in Nature Ecology & Evolution in March, found that the Pama-Nyungan language family originated in an area of northern Australia 5700 years ago—not 50,000 years ago, as one theory went.

But the mystery remains as to why it spread so thoroughly. Languages are known to expand through migration and technological advances, such as the development of agriculture, but the Pama-Nyungan family shows that large-scale language shifts can take place across hunter-gatherer societies.