Text 223, 80 rader
Skriven 2004-09-29 06:06:00 av R Norman (1:278/230)
Ärende: Re: Does restriction to s
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On Tue, 28 Sep 2004 15:54:16 +0000 (UTC), Elie Gendloff
<gendloff@optonline.net> wrote:

>On Mon, 27 Sep 2004 04:59:25 +0000 (UTC), John Leonard
><don't-spam-me-baby-jleonard2@si.rr.com> wrote:
>
>>Hello,
>>
>>	What is the opinion of the members of this group regarding this notion:
>>
>>	That sexual reproduction, of the kind that Humans practice, may 
>>increase the rate at which a species improves genetically as well as the 
>>rate at which it can adapt to changes in its environment.
>>
>>	Two suggested reasons for this effect are:
>>
>>1) 	This kind of reproduction creates a collection of individuals 
>>(almost) all of whom are genetically unique. This increases the range of 
>>genetic diversity from which to draw upon as a resource when confronted 
>>by an environmental challenge.
>>
>>2) 	Furthermore, male competition constitutes an additional stage of 
>>refinement that pits genomes against one another in order to measure the 
>>relative fitness of each.
>>
>>	I am asking this question because I am struck by the observation that 
>>Humans, although not necessarily superior to other species, seem to have 
>>"traveled the farthest distance" evolutionarily, of any species. At 
>>least insofar as cognition and information processing are concerned. It 
>>seems that we have gone "a greater distance" in this respect, from our 
>>starting point (of, say, the anemone?), than other types of organisms. 
>>All things being equal, I might expect organisms capable of asexual 
>>reproduction to be better equipped for survival since their line will 
>>not die out simply because they are separated from an individual of the 
>>opposite sex.
>>
>>	So, back to my question, what is the current opinion of practitioners 
>>in this field of the idea that restricting organisms to sexual 
>>reproduction may, in the long run, increase the rate at which they evolve?
>>
>A consequence of sexual reproduction is that the two sets of genes of
>the parents get reassorted by independent selection of each chromosome
>from either one parent or the other, as well as recombination by
>crossing over that occurs in meiosis.  By mixing up the genes in each
>individual, selection occurs more rapidly because there are more
>distinct individuals to select from.  In this way, sexual reproduction
>speeds evolution.  However, I would not say that humans are any more
>evolved than sunflowers.  Each solved the problems posed by their
>environment in different, but as complex, ways.
>
>
There are several problems in this answer, aside from the fact that it
was top-posted, a problem which I corrected.

First, the original question relates to sexual vs. asexual
reproduction and rates of evolution. Comparing humans with sunflowers
is inappropriate because we both practice sexual reproduction.  A real
comparison might be between humans (or almost any other multicellular
eukaryote and even many unicellular eukaryotes) with bacteria.  Even
that is not a good comparison because many bacteria have some form of
exchanging genetic material with a partner.

Second, it is true that sexual reproduction does produce novel
combinations of alleles that would otherwise be more difficult to
accomplish.  But it is not because there are more distinct individuals
to select from.  The number of different alleles in the gene pool and
their proportions are not influenced by sexual reproduction.

Google on "evolution sexual reproduction" or "advantage sexual
reproduction" and you will get a large number of discussions about the
biology.
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