huckturner{at}hotmail.com (Huck Turner) wrote in
news:c379at$1suj$1{at}darwin.ediacara.org: 

> I'm hoping that someone, if not Tim, can respond to some of the issues
> that I raised in my post (quoted below), which has gone without a
> reply for the last couple of weeks.
> 
> To summarise my point, if the fitness of a species is to be understood
> in the way that I've interpreted it (more descendant species means
> greater fitness), then a species property that increases the
> likelihood of speciation is still no more likely to be perpetuated
> than a property that decreases it. It would be a mistake to assume
> that as the number of species in a genus increases, the number of
> individual organisms in that genus will also increase. One does not
> entail the other. The number of species in a genus may increase even
> as it marches toward extinction. Species selection understood in these
> terms cannot therefore explain any properties of species.

A species property that increases the likelihood of speciation _is_ more 
likely to be perpetuated _unless_ it is linked to a lesser chance of 
survival of the offspring species - which may be the case, but needs to 
be explicitly stated. The question then is whether simply blindly 
increasing the number of species by sexual isolation mechanisms has any 
relation to the success of those species. There is an inverse 
relationship between the size of a population and its likelihood of 
surviving , so an increase in number of  species without increasing the 
total population size of all the species is unlikely to be 
successful.However there is a possibility that isolation allows for drift 
or directed selection or the Baldwin effect to move the newly isolated 
species towards different niches. In this case it is possible that 
increasing the number of species will not result in a concomitant 
decrease in their survivability, because the new species will move into 
new niches and increase their numbers. 


A downside of this type of speciation is that specialist species are more 
susceptible to variable conditions than generalist species, so any 
increase in overall numbers may be short-lived. The ideal might be a 
species that remains a generalist while spinning off specialist sub-
species. This might select for species with high developmental plasticity 
(so a minor change in the genes that control development could lead to 
ability to invade a new niche) combined with a moderate resistance to 
changes leading to sexual isolation and a high tendency to resist 
inbreeding, so the main population would remain generalist.

Yours,

Bill Morse
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