Corn as evidence of macroevolution (Doebley, Iltis, et.al.)?

bishopj at botany.washington.edu bishopj at botany.washington.edu
Thu Dec 16 18:02:05 EST 1993


In article <2eq30h$dkr at controversy.math.lsa.umich.edu> Doug Eernisse  
<Doug_Ee at um.cc.umich.edu> writes:
> 
> As an off-the-cuff response, you may want to distinguish between
> two concepts: 1) "macromutation" includes many varieties of mutations 
> except for the long-known point- or frame-shift ("micro") mutations; and 
> 2) "macroevolution" in which one is hypothesizing that species 
> are evolving through time in a way that is decoupled from "microevolution,"
> or _any_ change within a single population or species. This gets into

As I understand it, macroevolution simply refers to the evolution of any large  
phenotypic change.  According to Futuyma, it is a vague term, but usually  
refers to a change large enough to classify the lineage as a distinct genus.   
The controversy between advocates of punctuated equilibrium and neo-darwinists  
is whether macroevolutionary changes can be accounted for by microevolutionary  
processes (i.e. by a gradual accumulation of many changes each with relatively  
small effect) or if most macroevolutionary change is due to short bursts of  
very rapid evolution, possibly incorporating changes of relatively large effect  
or occurring by selection above the level of the population.  That is, the  
processes by which macroevolutionary changes occur are currently the subject of  
debate.

> debate about whether or not there are "emergent" properties of species.
> Do we gain anything by distinguishing the organismal level at which
> selection occurs among individuals (microevolution) from the level
> at which selection occurs among species (macroevolution)? As far
> as I know, paleontologists such as Steve Stanley and S. J. Gould have
> been the chief proponents of a macroevolutionary view, but this doesn't
> have much to do with the magnitude of a mutational event.
>  
> Doug

Another off the cuff remark:  In my book (unwritten and unedited), data which  
link the evolution of new species or significantly novel phenotypes (e.g. new  
organs or new enzyme pathways) to genetic changes within populations clearly is  
important to the causes-of-macroevolution debate.  This data won't often come  
by studying the genetic differences between widely divergent taxa, but rather  
will come from more closely related taxa.  I'm not familiar with the corn  
example that Ackerman requested an opinion on, but if the genetic change in  
question makes a large contribution to the difference between zea and teosinte,  
then it would seem important to the debate.  Since the two lineages are  
different genera, it might also fit in with definition found in Futuyma's text.   
Of course the amount of difference it takes to make two taxa different genera  
depends on the taxonomic group, the biases of the taxonomists, and in some  
cases can be based on very little genetic change


--

John Bishop
Department of Botany
University of Washington, Seattle
bishopj at botany.washington.edu



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