Four winged flies and Goldschmidt

thomasb at ento.csiro.au thomasb at ento.csiro.au
Tue Jun 15 11:40:04 EST 1993


>
>I believe that this is only one _hypothesis_ as to the mechanism of evolution.
>Some people think / have thought (eg. Goldschmit sp?) that evolution takes
>via. a mechanism (called punctuated evolution by Gould) which involves sudden
>catastrophic changes in a taxon giving rise to a new taxon.
>
>These changes could involve mutations in single genes with pleiotropic effects,
>especially in controlling genes that code for transcription factors.  Note
>that in Drosophillia sp? a single mutation can change this two winged fly
>into a four winged fly (just the opposite to what is supposed to have
>occurred during evolution ...
>
>A more coherent statement of this point of view can be obtained by looking
>up articles written by Gould and Goldschmidt ...
>
>Randall Tyers     tyersome at insect.berkeley.edu
>
>(also not an evolutionist - but I might be right anyway)



I thought I'd point out that, despite gross appearances, "four-winged"
flies arising from bithorax type mutations are not "revertants" to the
primitive condition of four wings.  The new metathoracic wings are not
metathoracic in morphology.  Instead, bithorax mutations create a second,
highly derived mesothorax from the metathorax.  Since this is definitely
not the primitive condition for that body segment in insects, arguments
that a few changes in loci such as bithorax are responsible for saltational
evolution of two wings, simply via supression of the primitive metathorax
are probably wrong.  The mutation creates a derived structure, and does not
reveal an underlying "primitive" developmental pathway. 

Goldschmidt had some precient comments along these lines concerning these
types of arguments with respect to antennopedia, etc. and generally
discounted these phenomena as indicative of the type of saltational change
that could occur.

Also, Gould et al.'s punctuated equilibria is a theory to explain
apparently rapid changes in the fossil record, and does not necessarily
entail saltational change, which is what preoccupied Goldschmidt. 
Punctuated equilibria is not equivalent to, nor does it require saltational
morphological change.

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Thomas M. Boyce  	       	       	       	       	      
thomasb at ento.csiro.au
Molecular Biology and Genetics  	       	       	       	Ph: 61-6-246-4159
Division of Entomology, CSIRO   	       	       	       	FAX: 61-6-246-4173
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