🚀 go-pugleaf

in article <677@ncsugn.ncsu.edu>, emigh@ncsugn.ncsu.edu (Ted H. Emigh) says:
> In article <2052@arthur.cs.purdue.edu> (Colin Jenkins) writes:
<<
<<On this point (and I am just as far out of my line at this point) I have 
<<trouble because such a breeding incompatibility would probably only come about
<<through radical genetic changes, rather than small ones.  I don't think that
<<evolution supports an idea of radical change, rather gradual changes selected
<<by the environmental factors to be passed on through reproduction.
< 
< Evolution "supports" whatever mechanisms are needed.  I know of no evolutionist
< that requires ALL changes to be small and gradual.  In particular, the
< speciation "event" most likely is quite radical (environmental if not genetic).

OK, however I wasn't talking about environmental changes, but rather individual
biological ones.  Radical changes of environment are easy to imagine as 
contributors to evolution.  I did not mean to imply that all processes that
contribute to evolution *must* be small.  When someone says a "radical" change
perhaps it should be qualified.  Change in genotype, or change in phenotype?
I was thinking strictly in terms of genotype.  The impression I get from the
idea of "radical" change is some new organism with a number of differences,
rather than a few.  Kind of like a snake born with legs and feet one day giving
rise to a whole new species of snakes with legs and feet (I presume that a
complicated change such as this would require many genetic mutations, rather
than a few).  Is such a "jump" viewed as a frequent and major contributor to 
evolution?  (That wasn't a facetious question, I'm really asking)

<<The other problem with this thought is that it seems to presuppose that the
<<mutant will be somehow aware of its reproductive incompatabilities and make
<<the fortunate choice of breeding with its relatives.  More complicated is the
<<fact that the none of the other relatives may have received the mutations, so
<<they should have just as much difficulty mating with the mutant as any other
<<normal organism.
<<
< I have before me a diagram (SCIENCE 1982, 215:1525-1530) which shows gives a
< comparison of the banding patterns of humans, chimpanzee, gorilla, and
< orangutan.  There are several remarkable things about the diagram.

	[Description of close chromosomal matching and differences,
	 and comments on inversions and some of their effects in
	 differing combinations on offspring ]

< What this means is the populations with small effective size can quickly
< become effectively reproductively isolated from their neighbors -- one of
< the conditions for speciation to occur.  (Obviously speciation can occur
< in other ways -- this describes just one way).
< -- 
< Ted H. Emigh, Dept. Genetics and Statistics, NCSU, Raleigh, NC

What you posted was very interesting, but I'm not sure what it says about the
correctness or incorectness of what I posted.  If the inversions you talked
about do produce radical genetic changes that can reproductively isolate
populations, what mechanism ensures that breeding takes place between 
compatible mates?

Perhaps a definition of terms would be instructive.  What do you mean when
you say "radical" change?


						Colin