THE story of the ascent of man usually casts Australia as the forgotten continent. Both archaeology and the genes of aboriginal Australians suggest that a mere 15,000 years were required for humanity to spread from its initial toehold outside Africa, on the Arabian side of the straits of Bab el Mandeb, to the land of Oz. The first Australians thus arrived about 45,000 years ago. After that, it took until 1788, when Captain Arthur Phillip, RN, turned up in Sydney Cove with a cargo of ne’er-do-wells to found the colony of New South Wales, for gene flow between Australia and the rest of the world to be resumed. This storyline was called into question a few years ago by the discovery, in some aboriginal Australian men, of Y chromosomes that looked as though they had come from India. But the details were unclear. Now a study by Irina Pugach of the Max Planck Institute for Evolutionary Anthropology, in Leipzig, and her colleagues, which has just been published in the Proceedings of the National Academy of Sciences, has sorted the matter out. About 4,000 years before Captain Phillip and his merry men arrived to turn the aboriginals’ world upside down, it seems that a group of Indian adventurers chose to call the place home. Unlike their European successors, these earlier settlers were assimilated by the locals. And they brought with them both technological improvements and one of Australia’s most iconic animals. Dr Pugach came to this conclusion by studying what are known as single-nucleotide polymorphisms, or SNPs. These are places where single pairs of the genetic “letters” that make up DNA often vary between individuals. (The letters themselves are chemical bases of four varieties, which pair up in specific ways, and which encode the instructions for making proteins, and thus living creatures.) SNPs act as markers for blocks of DNA that get swapped around during the process of sexual reproduction. Examining their pattern can therefore reveal a person’s ancestry—both where those ancestors came from, and when they lived. East India company

The first thing to emerge from Dr Pugach’s SNP analysis, which compared the DNA of aboriginal Australians with that of people from New Guinea, South-East Asia, India, China, West Africa and Europe, was that previous estimates of the time Australia was settled are about right. The ancestors of the first Australians, New Guineans and Mamanwa (a group who live in the Philippines), arrived in the area some time before 36,000 years ago, when the SNPs suggest the three lines parted company. This marked the original colonisation of an area which, though now an archipelago, was then mostly dry land because so much of the Earth’s water was locked up as ice in the extended polar caps of the last glacial period (see map).

The first colonists would thus have needed boats to cross some narrow seas in order to settle this land. But since their ancestors would have required similar craft to cross Bab el Mandeb, no technological improvement would have been required for them to do so.

Dr Pugach, however, also discovered something else. There is a pattern of SNPs in aboriginal Australians that is not found in people from New Guinea or the Philippines. But it is found in some Indians—particularly in Dravidian speakers from the southern part of the subcontinent. That discovery both meshes with the Y-chromosome data and enriches it, because the pattern of the SNP data meant that she and her colleagues could calculate when the Indian genes (and thus the Indians who carried them) arrived in Australia.

The answer is 141 generations ago. Allowing 30 years a generation, that yields a date of 2217BC. Obviously, this is not a precise date. But it is probably good to within a century or two. And that is interesting for two reasons. One is that the 23rd century BC is slap-bang in the middle of the period when Indian civilisation was emerging. The other is that it coincides with a shift in both the culture of Australia and the composition of the continent’s wildlife.

The bronze-age Indus valley civilisation, which reached its peak of development between 2600BC and 1900BC, is less well-known to outsiders than its contemporaries in China and the Middle East, partly because no one has managed to translate its written records. But it was no less successful, and it led—just as those two other areas did—to an urban culture that resonates today.

One technology it managed to develop was seaworthy ships, rather than mere boats, and Indus valley states used them to trade with their Middle Eastern neighbours. Such ships could have provided the means to get to Australia, either deliberately or by accident, for by then the sea had risen close to its modern level.

Archaeological evidence suggests that the Indus valley civilisation did not extend into the area where the telltale SNP patterns came from, so any connection is speculative. But many anthropologists believe Dravidians were once more widespread than they are today. (There is, for example, a group of Dravidians living south of Quetta, in Pakistan, on the edge of the territory occupied by the Indus valley civilisation.) In any case, Dr Pugach and her team could find no sign of the relevant SNP pattern in South-East Asia. That suggests the people who brought it may have travelled directly across the Indian Ocean, rather than coasting through what is now Indonesia. If so, they probably came by ship, rather than boat.

Pin it on the dingo?

The shift in Australian life came in three ways that can be seen today. One was that tools changed. It was not a case of metalworking being introduced, so an organised expedition of settlers from one of the Indus valley states can probably be ruled out. Rather, aboriginal culture, which had hitherto depended on the large and relatively crude stone tools of the palaeolithic, suddenly started using the smaller and finer ones of the neolithic. Whether the new arrivals did not know how to work metal, or merely lacked the equipment or sources of ore to do so, remains to be established.

The second shift was gastronomic. Sadly, the archaeological record has yet to reveal tandoori ovens or fossilised chapatis in Australia. But it does show changes at this time in the ways that cycad nuts—an important crop that Australians had long cultivated by the “fire-stick” method of burning vegetation that competes with the trees that bear them—were processed. Such nuts contain toxins. After about 2000BC several methods for removing these toxins, such as leaching them out with water and fermenting them away, spread through Australia. To this day, cycad nuts are familiar food in Kerala, in southern India. There, they are detoxified by being dried in the sun or by the fireside.

The third thing that arrived in Australia at this time was the dingo. The origin of these wild dogs, which are believed to have outcompeted and exterminated the native thylacine (also known as the Tasmanian tiger, because it lingered into modern times on that dingo-free island), has always been obscure, though their resemblance to certain breeds found in India is well known. Dr Pugach’s discovery suggests they may have come directly, on board ship. However, the existence of similar dogs in New Guinea and parts of South-East Asia complicates that explanation.

Whatever the truth turns out to be, though, this discovery is an intriguing piece of a jigsaw whose completed picture will reveal that truth. It is also an illustration of the power of modern genetics to write and rewrite the history books.