Text 1001, 48 rader
Skriven 2004-12-12 21:43:00 av Ekurtz99 (1:278/230)
Ärende: Re: The "fuel" of evoluti
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"Wirt Atmar" <wirtatmar@aol.com> wrote
> Someone wrote (I lost track in all of the quoting):
>
>>Why is this? Assuming populaton size to be constant, a single
>>parthenogentic type will, after predation etc have taken their toll,
>>produce 2 p-type offspring, whereas 2 sexual types, M&F, are required
>>to generate 2 offspring s-types. As Catherine Woodgold states, this
>>will lead to an exponential increase of the population size of
>>p-types, with corresponding decline and ultimately elimination of the
>>s-type.
>
> This statement can be found commonly in the biological literature as 
> well --
> and demonstrates more than anything else the relatively low utility of
> theoretical musings in biology (sometimes called "armchair biology"). You 
> can
> tell in an instant it's not true. There are relatively few fully
> parthenogenetic species in existence. Clearly, they're non-competitive on 
> the
> long-term.

Your laziness is not confined to biological musings. Had you studied more of 
the thread, you would have noticed that I mentioned parthenogenesis in order 
to point out the difficulty of defining "fitness" in terms of number of 
offspring. To quote myself:

" Consider the case of a sexual species into which a parthenogenic female is
introduced by mutation. Assuming that she and her immediate offspring
survive, and that the population size is constant, her offspring will
effectively displace the sexual type in a few dozen generations. But
ultimately the population will likely succumb to disease as a result of lack
of genetic diversity. So what is the "fitness" of the mutation that caused
the transformation? A meaningless question, in my view. The only thing that
matters is the probability at any time after the mutation is introduced that
its populational frequency has a given value. Without the introduction of
time and probability, no understanding of fitness is possible."

There is no need to make the case that asexual species are rare, since 
everyone knows that they are.
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