Factors Affecting Hominin Evolution Before 5 Million Years Ago: The Introduction of the Australopithecines

Some 5 million years ago during the beginning of the Pliocene Epoch climatic changes were causing African forests to progressively reduce their geographic coverage as grasslands, or savannas were advancing across the landscape.the genealogy of apes and human like creatures begin to leave a fossil record that signaled and divergence and the beginnings of separate developmental path.

Hominids were represented by the emergence of the genus australopithecines (southern ape) of which several varieties developed over time and emerged from the South African region as demonstrated by the many fossil findings in the proximate Great Rift Valley. These fossil findings showed that early hominins had almost human-like bodies below the neck but brains that were very little changed in size from those of apes. This point has been established in our previous postings but needs to be re-established to set the scene for the bifurcation of the australopithecine lineage into at least 2 evolutionary lines of hominins descended from the early australopithecines.

One line, often referred to as the gracile or slim and slender form included Australopithecus anamensis, Australopithecus africanus and Australopithecus afarensis. A. africanus and A. afarensis apparently were adapted primarily to lake margin grassland environments and had an omnivorous diet that increasingly included meat. Among them were our early human ancestors who started to make stone tools by this time.

The other lineage, referred to as the robust forms which included types such as Australopithecus aethiopicus, Australopithecus boisei and Australopithecus robustus lived more in mixed grassland and woodland environments, was primarily vegetarian much the same as their australopithecine fore bearers and had become extinct by about a million years ago.

What all australopithecines had in common among each of the various varieties, was a preference for bipedalism. In addition, they may also have used sticks and stones to fight, for they did not possess the type of canine teeth that would have made very imposing. Australopithecine brain cases were only capable of holding approximately 35% of the total volume that a modern human can contain. Australopithecines stood approximately four and a half feet tall. A very important point to consider about the Australopithecines was that their bipedalism came before the development of large brains, a factor long thought to be quite the opposite for many researchers and scientists.