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From: sarima@tdatirv.UUCP (Stanley Friesen)
Newsgroups: sci.bio
Subject: Re: Hominid evolution
Message-ID: <120@tdatirv.UUCP>
Date: 1 Feb 91 22:36:31 GMT
References: <106@tdatirv.UUCP> <6763@harrier.ukc.ac.uk> <111@tdatirv.UUCP> <6781@harrier.ukc.ac.uk>
Reply-To: sarima@tdatirv.UUCP (Stanley Friesen)
Organization: Teradata Corp., Irvine
Lines: 73

In article <6781@harrier.ukc.ac.uk> sss3@ukc.ac.uk (S.S.Sturrock) writes:
>In article <111@tdatirv.UUCP> sarima@tdatirv.UUCP (Stanley Friesen) writes:
>>Actually, it is by far the *most* complete fossil record of any vertebrate.
 
>HOLD IT, where did you get that?  The most complete fossil record of any
>vertebrate?  What about the mammoth, we actually have complete specimens
>of that.

We may have more complete *individual* specimens of the wooly mammoth,
but there are far *fewer* available.  I suspect that the combined sample
of A. afarensis alone exceeds that of thw mammoth, at least in terms of
number of individuals represented. (This is largely due to the discovery
of a mass-death site containing all or most of an A. afarensis band.)
Then, when you add all of the Asian Homo erectus specimens, the African
and European sapiens-erectus intermediates, the Neandertals, and the
various early Homo sapiens specimens and you have an impressive record.

> How many specimens of hominid species are there?  Not many, no
>wonder they can't generate a decent cladogram, not that it would mean anything
>if they did!

I agree with the latter.  And in some senses it is true that we do not
have 'enough' specimens, since there is no such thing as 'enough'.  But
the evolutionary trees (and species boundroes) have been getting *more*
not less clear as we get more specimens.  I have been trying for over a
year to come up with a satisfactory division of the early African Homo
specimens into species.  (These are the specimens usually considered
as Homo habilis and earliest Homo erectus). There appear to be at least
four different morphs included in the group (perhaps five).  Now, are
these geographic or temporal variants of a single species, or distinct
species.  Some of them almost certainly are distinct species, since two
of the morphs co-exist in the same beds.  Of course this *could* be sexual
dimorphism.  But if it is why do the other sites only have one morph each?
All in all a ticklish problem, and one that would not exist if we had fewer
specimens, since the bimodal ditribution would not be visible with a smaller
sample. (Nor do we have so many seperate fossil sites in so small a
time-space volume for any other group of vertebrates).

>You said yourself that A. afarensis may be a close relative of our direct
>ancestor, as I did.

What I heard you to say was that it was firmly established that it was not
a direct ancestor.  This is not so.  And if it is not, it is *extremely*
close to it, so close that it might not be distinguishable in the fossil
record.

> What about A. robustus if we are going to discuss
>hominid evolution, there have been all sorts of mistakes made with that
>one due to sexual dimorphism.  Look, there aren't enough specimens, no
>matter what you might think.  Besides I'm inclined to think that a lot of
>the problem is due to inadequate dating of specimens.

A. robustus, or as I call it Paranthropus robustus, is clearly a side branch,
as are all of the robust 'autralopithicines' (P. aethiopicus, P. boisei, and
perhaps one or two other species depending on interpretation).
[Hmm, here we have it again, slight differences in features between closely 
spaced samples - one species or two?]

> Species are just
>arbitrary groups *we* made, nature couldn't care less!  Before you get too
>anoyed, I am just playing devils advocate, I don't know one way or the other,
>there are people out there who think they do, I remain sceptical.

Hoo boy, as far as I am concerned, *species* are the *only* taxonomic
category that is truly 'real', in the sense that it corresponds to an
actual entity in nature.

All of the other categories, both higher and lower, are indeed arbitrary
to some degree.  [Even in cladistic analysis, since I have never seen
two cladistic analyses that agree unless they were by the same author].
-- 
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uunet!tdatirv!sarima				(Stanley Friesen)