From: kv07@IASTATE.EDU (Warren Vonroeschlaub)
Subject: Re: some stuff about fruit flies
Reply-To: kv07@IASTATE.EDU (Warren Vonroeschlaub)
Organization: Ministry of Silly Walks
Date: Fri, 9 Oct 1992 22:18:52 GMT

In article <7228@tekig7.PEN.TEK.COM>, alanf@tekig6.PEN.TEK.COM (Alan M
Feuerbacher) writes:
[quoting _Ghost in the Machine_]
>         The traditional explanation of this remarkable phenomenon is
> 	that the other members of the gene-complex have been
> 	`reshuffled and re-combined in such a way that they deputise
> 	for the missing normal eye-forming gene.'  Now re-shuffling,
> 	as everypoker player knows, is a randomizing process.  No
> 	biologist would be so perverse as to suggest that the new
> 	insect-eye evolved by pure chance, thus repeating within a
> 	few generations an evolutionary process which took hundreds
> 	of millions of years.  Nor does the concept of natural
> 	selection provide the slightest help in this case.  The
> 	recombination of genes to deputise for the missing gene must
> 	have been co-ordinated according to some overall plan....
which includes the rules of genetic self-repair after certain types of damage by
deleterious mutations.  But such co-ordinative controls can only operate on
levels higher than that of individual genes.  Once more we are drivin to the
conclusion that the genetic code is not an architects blueprint; that the gene
complex and its internal environment form a remarkably stable, closely knit,
self-regulating micro-hierarchy; and that mutated genes in any of its holons are
liable to cause corresponding reactions in others, co-ordinated at higher
levels.

  General rule of thumb: never trust elipsis.

  Ghost in the machine uses "Embryos and Ancestors"  QH371.D35e5 (deBeer, 1940)
as a reference for the above.  An old reference in 1968, much less nowadays.  It
is safe to say that the information in the book is almost certainly superceded
by more recent research(*), but let us see what the original reference read
anyway:

   [On homologous characteristics] Even where a character in two related
organisms can be shown to be under the control of a single gene, and this gene
can (by crossing) be proved to be identical in each, the characters may
nevertheless not be homologous in the recently accepted sense.  For it is
possible that the common ancestor may not have been due (as in the case of
'white eye' in Drosophila) to independent and parallel mutation in two stocks. 
Such cases would perhaps fall under the heading of 'latent homology', since the
fact of mutation at the same locus may reflect an inherited common tendency.
  A case of homologous genes controlling charactes which were independently
evolved and therefore not homologous has been demonstrated by Ford in _Triphaena
comes_.  This is a moth which is grey in colour on the mainland of Great
Britain.  Dark races have evolved in the Orkneys and in the Hebrides, and they
are under control of a gene which has proved by crossing to be identical in
both.  But crossing also shows that the manner in which these genes have come to
determine the dark colour is quite different in the two races, for subsequent
offspring from between them show a complete break-down in the gene-balance by
which the gene in question exerts its effect in the two races.  Each race has
therefore built up its gene-complex by selection in its own way, different from
the other.  Although the gene is the same in both races and its effects
apparently the same in both, these effects are not homologous in any sense.
  On the other hand, the control character normally effected by one gene may
come to be assumed by other quite different genes.  A good example of this
possibility is provided by the gene controlling the formation of the eyes in
Drosphila, the recessive alleomorph of which produces the eyeless condition. 
Nevertheless, in homozygous eyeless stocks, the other members of the
gene-complex can by breeding be *reshuffled and recombined in such a way as to
`deputize' for the absent normal allelomorph* to the `eyeless' gene, and eyes
reappear in the stock.  Such eyes must be regarded as homologous with the eyes
of normal wild stock, and therefore it is clear that homologous characters need
not be controlled by identical genes.

  Okay: first I would like to point out the asterisks mark the part of the
passage quoted in TGITM.  But more importantly go back and look at the `quote'
and the original.  Not only is it out of context, but changes the last few words
to make the conditions stronger.

  Now, being a mathematician I am subject to correction by any biologist, but
the gist of what is being said, compared to how it was presented in TGITM and
TBP, is different.  First of all, deBeer seems to indicate the new eyes were
bred for, they didn't appear by accident.  Secondly he makes it clear that it
was not the entire eye that was reconstructed, but just the one missing
allelomorph.  There is not a single mention of this being a common, much less
inevitable, result.  And if you read all the preceding text, and take the entire
discussion in context, it fits in rather nicely with genetics.

  My conclusion is that once again scientific sources have been misrepresented
to make claims that don't exist.  I will look up the new references, as it will
be best to double check what deBeer has said, but considering past records I'm
not holding my breath.

(*) I find it amusing that the longer quote actually goes about undermining an
author whose book it uses just a few paragraphs later.

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