Human Ancestors Hall: Alternate Phylogenies

Alternative Phylogenies
Robust Forms

Here are two alternate phylogenies implied by recent studies. Both are being supported in the paleoanthropological community by various researchers.
This first phylogeny represents an ancestor/descendent relationship where the robust forms descend from A. afarensis through P. aethiopicus, forming their own genus.

Phylogeny showing a robust clade of early humans

In this case A. africanus is distinct from all of the "robust" forms, and the genus designation Paranthropus is a valid genus name because all of its members are evolutionarily related to one another..

However, an alternative hypothesis supported by some research on the facial features of the South African fossils, implies that there were two distinct lineages of early humans that were regionally distinct: a southern African (A. africanus and P. robustus) and an eastern African lineage (A. afarensis and P. aethiopicus and P. boisei).

Phylogeny showing South and East African clades of early humans

For this hypothesis, each lineage evolved similar robust forms in parallel as the environment demanded that some populations of early humans needed to subsist on tough and fibrous foods. Thus, the similar chewing morphologies seen in P. robustus and P. boisei are not the result of a common ancestor, but of adaptations to similar environmental factors. Here, the genus designation "Paranthropus" would be invalid because it would include members of two totally separate evolutionary lineages..

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