Cladistic Effects of Reduced Gene Flow in the Earliest Years of Hominid Evolution


Jim McGinn

"Robert Karl Stonjek" <[email protected]> wrote

> But Haile-Selassie and his collaborators suggest that the
> teeth of these specimens indicate that they are very
> similar to A. kadabba. On the basis of the available
> evidence, they contend, all three may belong to the same
> genus or even species.
> A contrary view comes from David R. Begun of the
> University of Toronto, who counters that the A. kadabba,
> Sahelanthropus and Orrorin dentitions differ in important
> ways. "Rather than a single lineage, the late Miocene
> [hominid] fossil record may sample an adaptive radiation,
> from a source either in Eurasia or yet undiscovered in
> Africa, the first of several radiations during the course
> of human evolution,"

The base of the cladistics tree of human evolution is always
going to be/appear bushy. This is a direct consequence of
the fact that human evolution began when our chimpanzee-like
ancestors began to settle down into relatively separate and
geographically isolated communities which itself was a
direct result of the onset of the dry season of the monsoon
habitat, which began about 8 mya. This geographic isolation
dictated reduction in gene flow which shows up in the fossil
record as higher degrees of morphological variation between
members of the same species, similar to what we see with
respect to different breeds of dogs. And just as we don't
consider the morpholgical differences between a great dane
and a miniature terrier to be indicative of them being
members of different species we should not consider the
differences between different early hominid fossils to be
indicative of different species.