Re: Missing Link (was Human Chimp Gorilla)
Stanley Friesen (sarima@ix.netcom.com)
Fri, 12 Jul 1996 03:56:20 GMT
Mike Muller <muller@flmhh.ufl.edu> wrote:
>Homo erectus, as defined by the holotype, only exsisted in Asia. The
>African material has been lumped into the erectus group. But there are
>MANY morphological differences show it to be quite different.
I think I have to disagree with this - if understand it correctly.
Except for the earliest African specimens, most of the African H.
erectus is only subtly different from Asian H. erectus. I base this
statement on the detailed morphometric analyes in _The Evolution of
Homo erectus_ by G. Philip Rightmire.
See, for instance, Fig 37 in that book, which includes in the caption
the following statement: "Olduvai Hominid 9 departs from the
Zhoukoudian pattern in torus thickness but not in other measurements".
And in Fig. 38 the Sangiran (Java) specimens depart more from the
Zhoukoudian (China) specimens than do the Olduvai ones. And Fig, 35
shows more variation in the Javanese specimens (Sangiran versus
Ngandong) then between Sangiran and the Oldvuai series - again mainky
in the torus thickness.
Only the KNM-ER series (3733, 3883 and so on) along with KNM-WT 15000
differ enough from the Asian specimens to be even worth subspecific
recognition. The Olduvai specimens fall close to either the Sangiran
or the Zhoukoudian specimens in all cited measurements. And the later
Javan specimens (Ngandong) differ from all of the others in having a
significantly larger cranial capacity.
> And the
>most recent redating of the Asian material provide dates at 1.8-1.9 mya
>these are the same as the dates on the African material. Therefore the
>Asian material had to have left Africa prior to this in order to have
>developed such a different suite of characters.
There is a small fallacy here of assuming steady rates of divergence -
which I will take up in more detail below. But first ...
I suspect that African H. erectus came *from* Asia. That is I believe
that H. erectus evolved IN Asia and then immigrated to Africa. The
populations that left African would have been aprt of the Homo habilis
complex (perhaps the form sometimes called Homo rudolphensis).
How can this be? Simple - new species tend to arise in small
peripheral populations that have become isolated in habtitats that
differ somewhat from the ancestral habitat. Under these conditions
(small populations, high genetic drift, directional selection)
morphological change can be amazingly rapid. In fossil contexts this
is called "Punctuated Equilibrium".
Simply put, I would guess that the origin of Homo erectus was a
punctuation event - a rapid evolutionary transition, taking probaly no
more than 25,000 years (1,000 generations). Note, this is rather less
than the *uncertainties* in the dates of the earliest Asian H.
erectus!! This means that the appearance of H. erectus would be
virtually instantaneous, fossil-wise.
And since the pioneering H. "habilis" populations would have small and
localized, we can expect at best a few localized fragments of these
Asian habilines.
> New finds in China have uncovered teeth and tools that are akin
>the H. habilis in morphology and technology.
Yep - entirely consistant with hat I said above. These are probably
from the transitional habiline-H. erectus population.
And it may well be that a sub-population of the African H. erectus got
caught north of the proto-Sahara during a prior inter-glacial, and so
gave rise to Homo heidelbergensis/archaic Homo sapiens.
> I am currently writing an article for the "ORIGINS" site on Homo
>ergaster the African material currently being assigned to erectus.
If I accepted H. ergaster I would restrict it to the Turkana basin
specimens. The Olduvai and later North African specimens fall well
within the range of Javanese H. erectus.
The peace of God be with you.
Stanley Friesen
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