Re: The "fuel" of evolution

From: Catherine Woodgold (an588_at_freenet.carleton.ca)
Date: 11/29/04 

Date: Mon, 29 Nov 2004 05:22:43 +0000 (UTC)

"EKurtz" (NoJunk@ForgetIt.com) writes:
> 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.

Even if the parthenogenetic individuals average only 1.5
fertile offspring each, they will tend to take over the whole
population. The sexual ones could be declining while
averaging 1.8 offspring each, while the parthenogenetic ones
grow exponentially at 1.5 offspring each. So number of
fertile offspring is not a very useful definition of "fitness".

I hypothesize that sexual species alive today have characteristics
that make it difficult for parthenogenesis to occur, as a result
of billions of years of evolution in which species after species
was taken over by parthenogenesis and then succumbed to
changes in the environment better handled by sexual species.

It would not be an elaborate mechanism to prevent parthenogenesis;
that could easily be mutated away. It would have to be a more
subtle near-inability to mutate to parthenogenesis -- for example,
a chemical in sperm without which eggs cannot begin dividing,
not simply because the eggs respond to a "signal" -- the instruction
to wait for a signal could mutate away -- but because the chemical
is absolutely essential to cell division and the genome does
not specify the manufacture of this chemical in eggs.
Or something like that. Something that makes the sudden
appearance of parthenogenesis almost as unlikely as the
appearance of eyes in sightless species.

Sometimes an inability is an asset, as Pinker
explains in "How the Mind Works." 

--
Cathy

Relevant Pages

  • Re: The "fuel" of evolution
    ... >>Consider the case of a sexual species into which a parthenogenic female is ... Assuming that she and her immediate offspring ... Unless of course the mutation that causes parthenogenesis simultaneously ... Sexuality survives by default. ...
    (sci.bio.evolution)
  • Re: Did Darth Sidious create Anakin?
    ... Here's some of the excerpts of the articles on male offspring from ... these females can also give birth to male aphids without ... another instance of parthenogenesis that produces only male ...
    (alt.fan.starwars)
  • Re: The "fuel" of evolution
    ... >> offspring will effectively displace the sexual type in a few dozen ... advantage in terms of having more offspring - they invest less energy per ... offspring suffer higher rates of predation and especially disease. ... parthenogenesis does not have any advantage. ...
    (sci.bio.evolution)
  • Re: The "fuel" of evolution
    ... > organisms, tend to only exist for very short periods of time. ... quoted 2:1 advantage of parthenogenesis over sexual reproduction. ... sufficient to overcome the additional offspring of parthenogens. ...
    (sci.bio.evolution)
  • Re: The "fuel" of evolution
    ... >> But what if (as is normally the case for most organisms) the average ... >> invest less energy per offspring but that investment is not ... > to generate 2 offspring s-types. ... on this logic is that parthenogenesis would be more common in organisms ...
    (sci.bio.evolution)
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