Huli Wigman from the Southern Highlands, Painting of Tahitian Women on the Beach by Paul Gauguin
Many demographic models utilized in genetics are rather simple. Yet the expansion and retreat of various demes in post-Ice Age Europe seems to be far more complex than had previously been assumed, though I suspect part of the rationale for the original simplicity was a preference for theoretical parsimony in the face of a paucity of data. The landscapes traversed by our species are rich and topographically convoluted. Not only does the land vary, from plains, to deserts, to mountains, but the climate shifts radically over time and space. In the pre-modern age when humans were more dependent on environmental exigencies these fluxes in ecological and climatic parameters were essential in sharping the arc of human demographic expansion and contraction.
This is why a closer examination of the prehistory of Oceania is so appealing: here you have a physical geography which is radically constrained and so reduces the degrees of freedom of human movement and habitation. Unlike Europe, South Asia, or much of Africa, the time depth of the residence of the current indigenous inhabitants of Australia is on the order of 40 – 50,000 years. It seems likely that the indigenous people of the island of New Guinea to the north are from the same original settlement of Sahul, the ancient super-continent which consisted of New Guinea, Australia, and Tasmania. After the initial sweep out to the farthest reaches of what became Tasmania, there was a later push to the east of New Guinea, to the Solomon Islands,~30,000 years before the present. Then nothing for tens of thousands of years. The march of humanity seemed to stand still on the shores of the Solomons, just as the hominin lineage had once been cordoned off from Sahul by the forbidding seas between it and Sundaland, the Ice Age peninsula of Southeast Asia which was later submerged and became the western portion of Indonesia and Malaysia. The stasis was shocked by the Austronesians, a seafaring peoples who seem to have exploded out from somewhere between Borneo and Taiwan within the last 10,000 years, likely just on the margins of written history. The most famous of th Austronesian peoples are the Polynesians, who pushed across the Pacific, and likely even had some tentative contact with the New World. A less well known case is Madagascar, whose inhabitants speak an Austronesian language with clear affinities to a dialect of Borneo. The map below shows rough distribution of Austronesian peoples: