----- Original Message -----
From: "Tim Tyler" 
Newsgroups: sci.bio.evolution
Sent: Sunday, February 29, 2004 5:18 AM
Subject: Re: Article: Mammal mums can alter their offspring's sex


> Robert Karl Stonjek  wrote or quoted:
>
> > Read the rest at NewScientists
> > http://www.newscientist.com/news/news.jsp?id=ns99994708
> >
> > Comment:
> > The reason for gender selection is not, as the article seems to imply
(but
> > the paper being reported probably doesn't), by a conscious decision by
the
> > mother but by a process of natural selection (of the trait to choose)
that
> > has a benefit to the herd.  The mother receives no personal benefit
> > whatsoever by the breeding success or failure of her offspring.
>
> Her *genes* benefit.
> --
RKS:
That is not a *personal* benefit.  Besides, the gene combination that
resulted in her phenotypic expression are broken up by sexual recombination.
For a female to actually pass on her genes she would have to produce a
clone.  Genes that are beneficial to the male may not be beneficial to the
female, but the successful female's offspring is going to get a dose of
successful male's genes - some of the offspring may be superior to the
parents, some inferior, and some similar (on average) as one of the two
parents.

For the passing on of genes through sexual union the non-successful
offspring must fail, leaving only the offspring that actually do carry the
beneficial genes.  A lot of evolutionary biology thinkers seem to forget
this, imagining, perhaps, some sort of magic mechanism by which only
beneficial genes are passed on.  Lets not forget that each parent has a
diploid set of genetic material that contains expressed and possibly
unexpressed genes.  The beneficial genes that give the successful phenotype
its appearance and behaviour are not necessarily those that are contributed
by the female side, and the female allele is not necessary the one passed on
to or expressed in the offspring.

If the environment remains stable, then evolution effectively stops as
sexual reproduction will produce a set of offspring that vary to some degree
around an adapted medium, but never become more or less adapted.  Some
animals even revert to clonal reproduction as sexual reproduction is no
longer necessary (a cost which produces adapted and less adapted offspring).
In all some 15,000 species of animal can generate offspring without sexual
recombination, and at least a thousand (including some lizards and fish) are
completely asexual.  Numerous plants, such as 2,000 species of dandelions,
aspen, tulips and daffodils reproduce asexually (eg by budding).

Genes can not 'benefit' as such.  The spreading of genes as a mark of
success of that gene is a myth generated by some evolutionists who should
know better.  The most common form of evolutionary change is paelomorphic
and permorphosic changes in offspring.  This occurs when a slight variation
in Hox genes causes hypermorphosis, accelerated development,
predisplacement, progenesis, neoteny or postdisplacement.  The dodo bird,
for instance, is actually a type of pigeon that has hypermorphic beak,
accelerated development of the body, and Neotenic development of the wings.

Alleles are the next most common variation in offspring.  New genes and the
need for parents to make sure that these new genes proliferate in the
offspring represent such a tiny fraction of all genetic variation in
offspring that we are likely to only see it once in every few thousand years
in, say, humans.  In other words, new genes are extremely rare, variations
are common and in the gene pool so there is no advantage to the 'successful'
gene even if it does get passed on as it will likely be sharing the brood or
population with many others both having and not having that gene and only
chance determines whether that gene makes it through to the next generation.

On the other hand, a mother not having the successful gene expressed may
still have offspring that do have it as she may carry the gene but it is not
expressed, or the male may carry it.

Only when a change in the environment is included in the genetic inheritance
equation do we get evolution happening.  With a change in environment, more
offspring will die and the few that survive will have the genes required to
cope with the change.  Thus the concentration of the advantageous genes
increases in that population, the disadvantageous genes diminish until only
occasional recapitulation occurs.  In humans, for instance, it is rare to
see genes that would have been commonly expressed in our precursor species
expressed in modern times, but it has not completely stopped (but the
probability of the *combination* of genes that would have made our precursor
species distinct expressing in unison is negligibly small).

* some quotes in the above are from "Sexual Selection: Mate Choice and
Courtship in Nature" by James L. Gould and Carol Gould, and 'Shapes of Time:
The Evolution of Growth and Development' by Kenneth J McNamara

Kind Regards,
Robert Karl Stonjek.
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