December 04, 2008

Cranial robusticity in Australians

From the paper:
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

Darren Cunroe


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.



Antigonos said...

Here we go again!
The same old story!
No mtDNA or Y-DNA archaic Homo strain evident doesn't mean that it wasn't any!
When these geneticists are going to understand that THE LACK OF EVIDENCE OF CLUES DOESN'T MEAN THE EVIDENCE OF LACK OF CLUES!!!
Liking it or not the mtDNA and Y-DNA are highly affected by natural selection!
Variation in STR, depth of mutations etc. could be affected by genetic drift, bottlenecks, random mutations, and other parameters!!!
From an anatomically way of view the Australian fossils show diverce phenotypes and it is clear that more than two elements combined in the initial polulation. Keilor for example,a Tasmanoid, is completely different than Coobool Creek fossils and the Willandra fossils are much more archaic than Mungo although being much younger chronologically!!!
I believe that with our current knowledge on the Genetic attributes of our DNA we can't exclude a possible archaic Homo admixture to the early African Homo Sapiens Sapiens immigrnats in Australia. Besides, if modern Aboriginals have archaic admixture or not is irrelevant with what the first polulation of the island had back then!

terryt said...

I agree. For a start the researchers completely ignore the fact that the greatest fossil difference occurs during widely separated periods. And they seem to automatically assume that just because only 'modern human' haplogroups survive other genes from nearby don't survive.

And then they claim the DNA proves a single migration. Au contraire. The haplogroup pattern can easily be interpreted as showing at least two movements. One possibility is that Y-chromosome C and mtDNA haplogroup N arrived first. Followed by Y-chromosome K, and mtDNA M along with her descendant Q, and a line that had broken off N in SE Asia (P).

On the other hand it's even possible Y-chromosome C arrived more recently, with the Austronesian expansion. The Y-chromosome took off through the local population, but their language, and most of their genes, were lost as the Y-chromosome spread.

Resolving the Y-chromosome C tree would reveal a great deal about our evolution.

Ebizur said...

terryt said,

"Resolving the Y-chromosome C tree would reveal a great deal about our evolution."

That's definitely true. In the form of its various subclades, haplogroup C is the most important Y-DNA haplogroup of northeastern Eurasia, Polynesia, and Australia, and it has influenced to a greater or lesser extent all populations of Asia, the Americas, and Oceania. The distribution of Y-DNA haplogroup C is not just some fluke that can be ignored for the sake of preserving someone's pet theory. It is imperative that research on the internal phylogeny of haplogroup C be undertaken in order to elucidate the relationships among Asians, Americans, and Oceanians.

terryt said...

Thanks Ebizur. Even the fundamental divisions are unknown. C* and C1-C6 all separated at the same time according to any diagram I've ever seen. And that's extremely unlikely to be the case.

Ebizur said...
This comment has been removed by the author.
Ebizur said...

terryt said,

"Even the fundamental divisions are unknown. C* and C1-C6 all separated at the same time according to any diagram I've ever seen. And that's extremely unlikely to be the case."

Yes, that is the problem exactly. At least they have done enough work on haplogroup C to demonstrate that North/East Asians and Native Americans share the same subclade (C3-M217). None of the probable bifurcations in the phylogeny below haplogroup C-M130 and above subclades C1-M8 through C6-P55 has been resolved; all the subclades have been lumped together at the same taxonomical level. It's really a waste of a possibly enlightening source of information on the origins and migrational paths of a great number of modern human populations.

terryt said...

If it can be shown that C5, rather than C*, is the basal haplogroup this would provide evidence supporting the southern coastal route. As it stands we can only say that C* seems to hve originated around what would have been a virtually land-locked South China Sea at times of low sea level. How it got there is anyone's guess (spaceship?). The other C haplogroups, including C5, at present seem to result from a series of expansions from that region.