Text 777, 73 rader
Skriven 2004-11-13 02:49:00 av Tim Tyler (1:278/230)
Ärende: Re: Pleiotropy Enforces C
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Catherine Woodgold <an588@freenet.carleton.ca> wrote or quoted:

> That's just the sort of thing I was talking about
> when I posted the following, a long time ago:
> 
> Evolution of the speed of evolution.

[...]

> Consider a species where the female does all the work of 
> raising the children.  Now suppose a female suddenly arises 
> who can clone herself. All of her children are females with 
> exactly the same genes as herself, and also able to clone 
> themselves.  Instead of averaging one male and one female 
> surviving offspring as is average and normal in a steady 
> sexually-reproducing population, each clone would have on 
> average about two surviving female cloned offspring 
> (assuming that raising males is no harder or easier than 
> raising females).  So the number of clones would increase 
> exponentially, doubling each generation.

The so-called "two-fold cost" of sex.

> In either case, the clones would rapidly increase in number 
> and likely cause the extinction of the sexually-reproducing 
> part of the species, unless they can fill a different niche; 
> for example, the sexually- reproducing ones might save 
> themselves by having the males dislike mating with anyone 
> who looks like one of the clones.

That's not what usually what happens - usually the clones 
suffer from parasites - and don't do terribly well.

> We don't know yet whether humans now have the ability to 
> clone humans.  There's a slim chance that ethical, legal or 
> religious barriers will prevent it from being possible.  If 
> we do begin to clone, we will have lost a long-term 
> evolutionary advantage and have started down a slippery 
> slope towards being a less adaptable species.

Cloned organisms typically lack capacity for disease 
resistance (since they can't trade disease resistance genes)
and rarely do very well against sexually recombining strains -
/despite/ the fact that often twice the number of their
population can give birth.

That's Hamilton's "Red Queen" theory of the evolution of sex.

> Reproducing sexually is an altruistic act, helping out     
> someone elses' genes rather than one's own; but we can't  
> help doing it because we're made that way.  We can't easily
> evolve not to be altruistic in that way.

Sex is not altruistic according to the "Red Queen" theory - or 
the "gene repair" theory of the origin of sex (and these are 
the two main modern theories).

It /really/ pays a sexual organism to throw away half their 
genes in each generation. Failure to do so rapidly leads to 
problems in the short term - problems with error 
catastrophes - and problems with parasites.
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