Australia: The Land Where Time Began

A biography of the Australian continent 

Modern Australian hunter-gatherers – postcranial robusticity and sexual dimorphism

It has been assumed that elevated levels of postcranial robusticity and mobility patterns of sexual dimorphism that are observed in skeletal remains from the time when humans were hunter-gathers, which covers much of prehistory, to be the consequences of this subsistence strategy with greater robusticity and mobility being attributed to males than to females. Carlson et al. suggest that the origin of much of the basis for these trends were the populations where the skeletal correlates of patterns of activity are known, such as cross-sectional geometric properties of long bones, though their patterns of activity are inferred based on evidence such as archaeological records, e.g. those from the Pleistocene of Europe. As there is ethnographic documentation available of the patterns of activity of Australian hunter-gatherers Australian populations provide an opportunity to assess these ideas critically. In this paper Carlson et al., discuss the questions of whether or not the postcranial skeletons of Australian hunter-gatherers express elevated levels of postcranial robusticity and sexually dimorphic mobility compared to other populations from similar latitudes, and whether or not these findings are supported by ethnographic accounts. Cross-sectional images were obtained of 149 skeletal elements that included humeri, radii, ulnae, femora, and tibiae by the use of CT scans. Image data were used to calculate cross-sectional geometric properties and standardised for body size. It was found that in the postcranial skeletal material of Australian hunter-gatherers there is often reduced robusticity at the femoral and humeral midshafts relative to (Khoi-San), agricultural/industrialised (Zulu), and (African American) groups. There is more sexual dimorphism of the upper limb robusticity than robusticity of lower limbs displayed by Australian hunter-gatherers. Carlson et al. say it is premature to attribute specific behavioural causes to sexual dimorphism of upper limbs, though sexual-specific differences in tool use are supported by ethnographic accounts. Sexual dimorphism is virtually absent in robusticity of the lower limb, which is supported by ethnographic accounts of high mobility among males and females where mobility is seen to be equivalently high. Therefore, elevated postcranial robusticity and mobility that is sexually dimorphic are not always characteristic of hunter-gatherers.

Conclusions

Elevated postcranial robusticity is not exhibited in Australian Aboriginal People relative to forager, agricultural/industrialised, and industrialised populations that have similar body builds. This is consistent with the idea that in Aboriginal Australians rugose muscle attachments rather than thick limb bone diaphysis are what underlies the conception that Australian Aboriginals are robust postcranially (Collier, 1989; Pearson, 2000). Elevated postcranial robusticity therefore need not be a characteristic of a hunter-gathering subsistence economy, at least in respect of the cross-sectional geometry adjusted for body size.

Significant sexual dimorphism of the upper limb midshafts (humerus and radius) is displayed by the cross-sectional geometric properties of long bone diaphyses of Australian Aboriginals, though in the lower limbs there is comparatively little sexual dimorphism. Significant sexual dimorphism is not observed in either limb, which contrasts with the measured robusticity patterns. Robusticity differences between Australian Aboriginal females and males are indicated by results to be restricted to the upper limb and in the lower limb they had loading patterns that were relatively equivalent. Carlton et al., suggest that this is a reflection of equivalent level of mobility, as in distance travelled, or possibly a compensatory effect of the females carrying burdens, both of which are supported by ethnographic accounts.

Sources & Further reading

1. Carlson, K. J., et al. (2007). "Robusticity and sexual dimorphism in the postcranium of modern hunter-gatherers from Australia." American Journal of Physical Anthropology 134(1): 9-23.