[Taxacom] The Difference

B.J.Tindall bti at dsmz.de
Mon Oct 29 09:45:03 CDT 2007


The article which is often taken as the reference 
work for the introduction of molecular data in 
evolutionary analysis is an article by 
Zuckerkandl and Pauling, 1965. Careful reading 
indicates that while advocating the use of the 
molecular data (in those days protein sequences) 
they didn't exclude non-molecular data sets. A 
key phrase in that paper also indicated that 
complexity was a central issue. Pity one lost 
sight of that aspect over the decades.
Brian

At 03:34 29.10.07, Kenny Kinman wrote:
>Dear All,
>       I only had time to quickly skim through this thread, but I am a little
>concerned that both morphological and molecular (especially the latter) are
>being painted with brushes that are too broad.  Molecular data now has a
>range from the simple (single base substitution), through slightly more
>complex (insertions/deletions of one or more bases, generally the longer the
>better), to very complex insertions/deletions that can be quite long
>(sometimes even entire sections of chromosomes).
>
>      I think the real issue here should be complexity of a character, not
>whether it is morphological or molecular.  If a molecular data set includes
>only simple base subtitutions, then it shouldn't be mixed with complex
>morphological characters (or even complex molecular characters, for that
>matter), at least initially.  You can then go ahead and mix simple and
>complex characters in another analysis, but you'd better weight them in AT
>LEAST some crude fashion (low weight, moderate weight, high weight).
>
>       But there are now complex molecular characters that are probably far
>more reliable than some simple morphological characters, so the ideal
>analysis would include all complex characters (morphological and molecular).
>   If you want to include simpler characters (of either kind), you'd better
>weight them appropriately so they don't dilute the phylogenetic signal from
>those that are more complex.
>      ---Ken Kinman
>
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