Re: Lumper or Splitter?
Phillip Bigelow (bh162@scn.org)
Sun, 08 Dec 1996 23:51:52 -0800
Rohinton Collins wrote:
>
> 1. Is the 'hit-and-miss' process of classification of fossil taxa more
> likely to lead to lumping or splitting?
>From a paleontological perspective, I would say it leads to
excessive splitting. Generally unavoidable, but none-the-
less very excessive.
>
> 2. Is it safe to assume that variation within extinct taxa would be similar
> to the variation seen within extant taxa, bearing in mind that millions of
> years may separate fossils believed to be in the same species?
>
As far as I am concerned, yes. The only down-side of course,
is the missing soft-tissue data in the paleontological record.
Some of the soft-tissue data can be approximated from muscle-scar
insertions on the bones, pelvic width, cranial capacity,
etc., but much data is gone forever. And the soft tissue data one
gets from paleontology is very crude compared to the abundance of
data taken from modern zoological specimens.
> 3. Following on from 1 and 2, do you think that the specimens classified as
> H. habilis are representative of a single species?
Don't know enough to meaningfully respond to that one.
> I think that it is dangerous making any hard and fast rules about
> classification of extinct taxa.
I disagree. Because of the extremely limited amount of information
that we can gleen from fossil animals, rigid classification rules
are extremely important.
Even more important is to expose paleontology's limitations.
For instance, the probability of a fossil taxon being assigned as a
new species (when in reality, it should be assigned to a new genus if
we could study the soft tissues of the animal) is very high in
paleontology.
>With extant species we can test for
> inter-fertility. This is not possible with extinct species. The fact that a
> species may span several million years makes this irrelevant anyway. For
> example early eastern H. erectus specimens may differ sufficiently from
> later H. erectus for some to identify them as different species. Has
> speciation occurred? How long before speciation may be said to occur in a
> species experiencing gradual evolution (as opposed to punctuated
> equilibrium when a species with a markedly different morphotype arises in a
> very short period of time)?
There is a distinct possibility that the early Homo species
were extremely close genetically (sort of a like an early African
version of the multiregional hypothesis). The earliest habilis/erectus
situation, for example, may simply be a case of two distinct
populations simultaneously undergoing anagenesis, while
occasionally interbreeding. Although H. habilis is found in
slightly older rocks than erectus, because of the small sample
number, this situation may be more of a sampling artifact than a
true approximation of a distinct temporal range. Finding more
Homo specimens will clear up these little ambiguities.
My personal interest lies in these questions: How much branching
is there in the genus Homo? Did early or even late speciation occur
within our genus, or is everthing we are finding suggesting
a single straight-line of Homo evolution? And, most importantly, is
the time-resolution and precision within the fossil record high
enough to answer these questions? I have a hunch that it is.
<pb>
|