The comparison of the bone structure of two early human finds in South Africa suggests, according to a study involving KL researchers, that the development from tree to terrestrial form of living and thus climbing to walking upright in early humans may not have been linear. This was demonstrated in a recently published study using the worldwide unique software to examine bone structure and density, developed by Professor Dieter Pahr, researcher at KL Krems and TU Vienna.
A team led by Matthew Skinner from the University of Kent (Great Britain) examined the inner structure of the upper ends of the thighbones, which are part of the hip joint, in two early human finds from South Africa. One of them is older than two million years (2 to 2.8 million years), the other probably 1.5 million years old, according to Prof. DI Dr. Dieter Pahr, professor at the Department of Anatomy and Biomechanics at Karl Landsteiner Private University for Health Sciences in Krems and at the Institute for Lightweight Structures and Structural Biomechanics at TU Vienna, who is co-author of the study.
When examining the archaeological finds, the outer shape of the hip joint part of the thigh clearly shows that the individuals were able to walk on two legs well. But how they really moved during their lifetime can be better read from the inner structure of the bones. There are small beams of bone tissue (trabecula) which change their shape during the lifespan according to the load. The researchers compared their arrangement in the two fossils with that of chimpanzees, bonobos and gorillas, which both walk and climb on all fours, as well as orangutans, which spend most of their lives climbing, clutching and hanging in trees, and modern humans. "The human comparative samples are a few hundred year old bones where people were physically very active," explains Pahr.
STW522, i.e. the older Australopithecus find, shows an internal structure similar to that of a modern human, and therefore did not climb much like a monkey, the researcher explains. In contrast, the bone of early man STW311, who probably lived half a million years after STW522, shows an internal density arrangement that suggests a combination of climbing and walking, like an ape.
According to this, the ancestors of humans did not at some point change from the trees to an earthbound life, they were either drawn into the trees again and again, or bipedality developed repeatedly.
Link to the study: http://dx.doi.org/10.1073/pnas.1914481117