Instead, cranial robusticity among the Australians and other modern humans can reasonably be explained on the basis of current knowledge of cranial development-function, as well as a phylogenetic scenario consistent with genetic studies of the population history of Aboriginal Australians (e.g. Hudjashov et al., 2006). Thus, the earliest Australians might be thought of as having evolved from the earliest modern humans who migrated from Africa into East/Southeast Asia around 60-70 kyr. The Australian Pleistocene/Early Holocene human record indicates the presence of marked variability in cranial form. However, it is not possible with present genetic data to determine whether the continent was colonised during a single migration by a population with a highly variable cranial form or in two major events by people with different cranial morphologies.From Hudjashov et al. (2007) mentioned in the text:
The analysis reveals no evidence for any archaic maternal or paternal lineages in Australians, despite some suggestively robust features in the Australian fossil record, thus weakening the argument for continuity with any earlier Homo erectus populations in Southeast Asia. (ii) The tree of complete mtDNA sequences shows that Aboriginal Australians are most closely related to the autochthonous populations of New Guinea/Melanesia, indicating that prehistoric Australia and New Guinea were occupied initially by one and the same Palaeolithic colonization event approximately 50,000 years ago, in agreement with current archaeological evidence. (iii) The deep mtDNA and Y chromosomal branching patterns between Australia and most other populations around the Indian Ocean point to a considerable isolation after the initial arrival. (iv) We detect only minor secondary gene flow into Australia, and this could have taken place before the land bridge between Australia and New Guinea was submerged approximately 8,000 years ago, thus calling into question that certain significant developments in later Australian prehistory (the emergence of a backed-blade lithic industry, and the linguistic dichotomy) were externally motivated.Journal of Archaeological Science doi:10.1016/j.jas.2008.11.021
Possible Causes and Significance of Cranial Robusticity Among Pleistocene-Early Holocene Australians
An analysis of possible developmental-functional causes of cranial form suggests that the unusual morphology of ‘robust’ Pleistocene/Early Holocene Australians such as Willandra Lakes Human 50 might best be explained by four underlying factors: possession of a 1) large neurocranium, 2) narrow cranial base, 3) viscerocranium with considerable midfacial projection, and 4) large dentition, especially the cheek teeth, with their associated large jaws and high volume masticatory muscles. Some of these features are likely to be highly heritable, while others are caused/exaggerated by influences from ageing processes, diet, and a hunter-gatherer lifestyle in an arid environment. These underlying ‘causes’ are either apomorphies of H. sapiens (1 & 2) and thus absent from pre-modern specimens such as from Ngandong, or represent plesiomorphic features of latter Homo (3 & 4). It is concluded that combining current knowledge of cranial development-function with genetic studies of the population history of Aboriginal Australians provides the most parsimonious solution to understanding their evolutionary origins.