On Sat, 8 Jul 1995 11:20:25 -0400 you wrote:
>Abstract: Documentation of noncontinuum evolution
GM>Developmental Biology by Scott F. Gilbert (Sunderland, Mass.:
Sinauer
>Associates, Inc., 1991). I have not had time to read the book yet, but late
>last night after Jim's challenge that this could not be documented, I looked
>at the last chapter of this book. Gilbert says,
>
>"In many ways, the phenotypes of the homeotic delections resemble the
>postulated earlier stages of _Drosphila_ evolution. _Drosphila, a two-winged
>(dipteran) fly, is thought to have arisen from normal four-winged insects
>(pterygotes). This condition can be acheived by deleting the _Ubx_ portion
>of the bithorax complex. Winged insects are thought to have evolved from
>nonwinged (apterygote) insects. This situation is mimicked by the deletion
>of the _Antennapedia_ gene, in whose absence all the thorax develops like the
>wingless first thoracic segment. The apterygote insects are believed to have
>arisen from myriapod-like creature (millipedes, centipedes), a situation
>similar to the phenotype generated when the entire bithorax complex is
>missing and the entire posterior of the embyro develops like a legged thorax
>segment. Finally, if both sets of homeotic genes (the _Antennapedia_ and
>_Bithorax_ complexes) are removed, the result is a condition similar to that
>of the most primitive known arthropods, the onychophorans. As Raff and
>Kaufman (1983) have said, "Thus, by sequential deletion of a relatively small
>amount of genetic material we have managed to traverse a rather large amount
>of evolutionary ground.""( p. 835-836)
>
GM>Two observations: 1) If by the addition of new parts to the
>homeotic genes, major morphological change occurs, then the constant
>claims by anti-evolutionists for more and more transitional forms may
>be based on an outdated view of genetics
>2) This type of small "genomic" change = large phenotype change, is
>exactly what is seen in those programs I wrote and made available to
>the reflectorites.
Again we have this "it must be evolution" argument!,:-) No one denies
that changes to genes can produce changes to forms. If you could add,
subtract, mutliply and divide fruit-fllies genes enough you could
presumably make any living thing?
You call this a "small genetic change". A single-step change that
these scientists have done with intelligent planning and execution, is
an argument for special creation, not naturalistic evolution.
The question is, did the "small genetic change" you have referred to,
actually happen in nature, and did it happen by purely naturalistic
processes? When? Where? How?
None of this is new. GGould discusses it in "Hen's Teeth and Horse's
Toes", under the heading "Helpful Monsters". It is interesting that
he does not claim this is necessarily how evolution occurred:
"G Homeotic mutants are gripping in their weirdness, but what do they
teach us about evolution? We must avoid, I believe, the tempting but
painfully naive idea that they represent the long-sought "hopeful
monsters" that might validate extreme saltationist views of major
evolutionary transitions in single steps (a notion that I, despite my
predilections for rapid change, regard as a fantasy born of
insufficient appreciation for organisms as complex and integrated
entities). First of all, most homeotic mutations produce hopeless
creatures. The legs that extend from antennal sockets or surround
mouths in afflicted flies are useless appendages without proper neural
and muscular hookups. Even if they did work, what could they
accomplish in such odd positions? Secondly, the viable homeotics
mimicking ancestral forms are not really forebears reborn. A bithorax
fly bears the ancestral complement of four wings, but it attains this
state by growing two second thoraxes, not by recovering an ancient
pattern." (Gould S.J., "Hen's Teeth and Horse's Toes", 1984, Penguin,
p194)
God bless.
Stephen
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