Who were the first humans in Sahul and how did their genomic composition reflect diverse processes of admixture on the Asian mainland? What were the points of entry and how many streams can we identify? How quickly did humans spread out across the landmasses that are now Australia and New Guinea, and by which routes and what dates were the various more challenging environments reached? What role did climate change and past environmental dynamics play in shaping the movement and adaptation strategies of people as they traversed major biogeographic barriers such as the Wallace Line and the arid centre of Australia? Was cultural adaptation to the radically new environments of the Sahul rapid, or was it scaffolded by a relatively long occupation of zones that were more commensurable with the recent pasts of these people? What is the deep history on the northern side of the Arafura Sea, which served as the springboard for peopling Sahul some 60,000 years ago, but which has also seen the westernmost and most recent migrations of Papuan speakers? Archaeological findings, though constantly expanding in range (and perhaps in time-depth), have not yet been integrated with data from the fields of linguistics (‘time-horizon problem’, see above), palaeoecology (climate-fire-human-ecosystem interactions through time), anthropology (modelling of small-scale group dynamics), and genetics (lack of data from non-Pama-Nyungan languages). Can we bring evidence from those fields into the picture, to give us a fuller picture of this primal phase of human presence in our region? What were the human responses to these environmental changes? Did the distribution of linguistic and cultural diversity before this division anticipate the very different linguistic and cultural pictures we find currently on the Australian and New Guinea sides – in other words, were New Guinea and Australia already very different beforehand? Or do these pictures reflect different and more recent trajectories of cultural evolution, which have led what was originally a more homogeneous cultural fabric (or one with a more gradual differentiation from north to south) to evolve in quite different directions on opposing shores of this narrow sea? Do we find traces of ancient trans-Sahul connections in the linguistic, genetic or archaeological records? How closely tied are the environmental, linguistic and cultural trajectories of change during a period of dynamic and rapid transition from the late glacial to the Holocene? 

One of the most striking aspects of this whole picture is the remarkable cultural separation of New Guinea cultures from their Australian relatives, given their relatively recent physical separation. When, why and how did Australia and New Guinea acquire their distinctive regional characteristics? Within this major cultural and geographic divide, there are two remarkable processes that distinguish the more recent cultural evolutionary history in Australia and New Guinea. In Australia, although there is archaeological evidence of human settlement across the whole hemi-continent 50-40,000 years before present, linguistic diversity suggests a more recent cultural sweep. Languages from a single family, the Pama-Nyungan languages, cover seven-eighths of the continent while around 25 other groups are crammed into the northwestern one eighth. The drivers of Pama-Nyungan expansions remain enigmatic and explanations fail to integrate well across disciplines: linguists have proposed mid-Holocene dates while the genetic data suggests populations within Pama-Nyungan look stable for much longer. How can these two different narratives be reconciled? Could the the radical environmental changes resulting in the flooding of Lake Carpentaria, and the submerged glacial landscape of the contemporary Arafura Sea and Torres Strait, have prompted not only a cultural expansion of Pama-Nyungan speaking peoples, but the total replacement of the earlier cultures that arose from the initial colonisation event (Topic 1)? In contrast to New Guinea, there is no agricultural revolution linked to the Pama-Nyungan expansion, though there is some, though controversial, suggestions of an intensification of resource use in the Holocene. Do technological or subsistence changes in the archaeological record align with the hypothesis of cultural expansion and replacement? Did the dingo arrive in Australia before, during or after the Pama-Nyungan expansion? Is there a signature of ecological change that might indicate a radically different way of exploiting the landscape associated with a cultural sweep? 

But to really understand how evolution works we need to document change and diversification in progress, and this topic focusses on that issue for two areas where the relevant forces can still be observed thanks to the maintenance of cultural and linguistic dynamics in relatively traditional forms: Southern New Guinea, and Arnhem Land. The causal drivers of these dynamics are both complex and interactive. These include the uses of language differentiation to index and maintain social differences, such as between clans and larger aggregates, the role of multilingualism as a vector of both divergence and convergence, the uses of material culture (such as different styles of manufacturing stone tools, or different conventions in painting or music) to index social group membership. These drivers interact with different patterns of social organisation, kinship, group affiliation, language affiliation and population genetic profiles. Important too are the various forms of feedback between group and intergroup dynamics, and the development of linguistic and material-culture differentiation.