More taxo-computational distractions
magnus.liden at SYSTBOT.GU.SE
Mon Dec 1 11:40:04 CST 1997
Hej svejs Thomas Schlemmermeyer <termites at USP.BR>,
you brought up one of my pet subjects in your recent TAXACOM communication.
>"This taxon X or Y, which previously was considered basal, generalized,
>archaic ec. ec. member of the group, unfortunately, is not a good window to
>the past, as there are many characters which are difficult to resolve
>(wether they are apomorphic or plesiomorphic)."
The term "basal" appplied to a cladogram/phylogenetic tree only designates
a clade (or OTU) that is sistergropup to a large and speciose (or better:
OTU-ose) clade in an assymetric tree. It bears no connotation what-so-ever
to degree of "primitiveness". Only CHARACTERS can be labelled plesio- or
apomorphic, not TAXA! An isolated "basal" branch should be expected to be
on average just as "advanced" as any other OTU. There is no logical or
biological reason to expect a priori that some OTUs are more "archaic" or
"generalized" than others.
This common misconception is, I believe, partly coupled to the
(non-supported and rather mystical) idea that the rate of anagenesis is
directly coupled to the "rate of cladogenesis" (which in turn is believed
to be, on average, correlated to the number of extant recognized OTUs in a
>SO: Are there any good windows to the past?
>Are there phylogenies where it really functions somewhat like this:
>Many groups which have a lot of apomorphic characters, but some extremely
>basal, more plesiomorphic groups which may serve as "windows to the past".
>I want to get examples from the whole bandwidth of biological systematics
> "WINDOWS TO THE PAST"
I advice you to be extremely suspicious about all such claims (especially,
but not only, if tree topology is used as an argument), as they are usually
based on circular reasoning, and a preconviction that such "windows" are to
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