During glacial times, the Indonesian islands were joined to the Asian mainland, but Australia wasn’t. It’s likely that by 50,000 ya, modern humans inhabited Sahul—the area including New Guinea and Australia. Bamboo rafts may have been used to cross the ocean between islands, and this would certainly have been dangerous and difficult. It’s not known just where the ancestral Australians came from, but as noted, Indonesia has been suggested. Human occupation of Australia appears to have occurred quite early, with some archaeological sites dating to 55,000 ya. There’s some controversy about the dating of the earliest Australian human remains, which are all modern H. sapiens. The earliest finds so far discovered have come from Lake Mungo, in southeastern Australia . In agreement with archaeological context and radiocarbon dates, the hominins from this site have been dated at approximately 30,000–25,000 ya.
Fossils from a site called Kow Swamp suggest that the people who lived there between about 14,000 and 9,000 ya were different from the more gracile early Australian forms from Lake Mungo . The Kow Swamp fossils display certain archaic cranial traits—such as receding foreheads, heavy supraorbital tori, and thick bones—that are difficult to explain, since these features contrast with the postcranial anatomy, which matches that of living indigenous Australians. Regardless of the different morphology of these later Australians, new genetic evidence indicates that all native Australians are descendants of a single migration dating back to about 50,000 ya (Hudjashou et al., 2007).