Hypothetical ancestors

[Richard Zander]

Enlightened cladists do not "discover" ancestors among internal branches in
the cladogram. A cladogram is more like the results of a cluster analysis
but with branches of different lengths. Although ancestors may be inferred
to be somewhat similar in character to the characters assigned the ancestral
branch, more information is necessary for an exact characterization.
Basically, cladograms group closely related taxa, inference of any more than
this without more data is pretty iffy.

If a terminal taxon has no autapomorphies, it may be inferred to be a
surviving ancestor. But given the ambiguities introduced by difficulties in
telling just when changes occur (difference between ACCTRANS and DELTRANS in
Paup), and given the lack of information on just which ancestral
autapomorphies become their descendants' synapomorphies and which are lost,
ancestors are pretty ghostly as hypotheses.



---------
From:
Richard H. Zander
Emeritus Curator of Botany
Clinton Herbarium
FNA Editorial Center at Buffalo

The Buffalo Museum of Science
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----- Original Message -----
From: "Bryan Simon" <Bryan.Simon at ENV.QLD.GOV.AU>
To: <TAXACOM at USOBI.ORG>
Sent: Sunday, February 10, 2002 11:27 PM
Subject: Hypothetical ancestors


> Cladistic analysis gives us clades in which the end-point taxa (be they
> families, genera, species or any rank in between) represent extant taxa.
> The region on a cladogram at which two clades diverge is given the
> theoretical definition of a "hypothetical ancestor". In view of the
> extremely large number of biological species in the world, surely it
should
> be possible that we actually come across these very ancestors in a few
> cases, or am I being naive?  This would assist greatly in answering
critics
> among creationists who often pose the question "What happened to or how
> come we never see the intermediates that must have been present at some
> stage to be able to account for the evolutionary process?"  These
ancestors
> presumably can also be fossils?  Are there papers in the literature that
> could provide me with useful information?
>