From: mongo@PDaXcess.techbook.com (Mongo)
Subject: Re: Bales' Scales
Organization: Portland Public Access sponsored by TECHbooks Bookstore
Date: Thu, 16 Apr 1992 20:09:23 GMT

[At the end of this article, I outline J.  Dycks  theory  of
feather  evolution  in  which  all  of the intermediates are
advantageous. Since Bob Bales claims no such theory is  pos-
sible,  leaving  divine  fiat  the only option, I am sure he
will find this of interest]
 
BB: >This reference states that reptilian scales are homolo-
gous  to a different >structure than feathers themselves and
that feathers come from a different >layer.
 
BB: >The issue is the skin  layer,  not  developmental  con-
trols.  I'll say more >about this in another article.
 
Nope, the issue is homology. Your claim is that since scales
arise  in a different _sub_layer of skin, feathers cannot be
homologous to scales.  Checking a dictionary,  we  see  that
homologous  means  'has  corresponding  developmental role'.
Given that definition, whether feathers and scales obey  the
same developmental controls is relevant - more relevant than
final precise location.
 
Now you have managed to locate one scientific  opinion  that
they  are  not  homologous.  Since science, unlike religion,
does not proceed by appeals to authority, that does not set-
tle  the  question. It turns out that there is more than one
opinion in the literature - and the literature I  have  con-
sulted  is  more  recent  than yours[1]. Books trail journal
articles by at least 2 years.
 
(By the way, Bob, the issue of differing skin sublayers is a
red  herring. Just because a feature evolved in one location
doesn't mean a mutation can't move it to another - There  is
a  common  mutation  in  drosophila that causes legs to grow
instead of antenna - but let us proceed anyway)
 
Support for the idea that feathers  began  as  an  outgrowth
from scales can be found in the following observations:
 
(1) In some cases, feathers grow within the  area  delimited
by a scale, that is out of a scale. "This can be observed on
the legs of many species, on the lateral  skin  of  struthio
embryos  and on the pectoral callosity of rattite birds... A
gradual transition from naked scales to scales with feathers
can  be observed in some species. Where this is the case, it
appears that feather and scale  are  supplementary  to  each
other, so that the degree of development of one is inversely
proportionate to the degree of development of the other.
 
(2) In recombination experiments where leg dermis and dorsal
epidermis are associated, scales with feather outgrowths are
formed under certain conditions.
 
So much for feathers and scales being unrelated structures.
 
J. Dyck presented the following theory of the  evolution  of
scales (one of two, but I found this one more convincing):
 
(1) The growth of conical outgrowths on the  free  edges  of
the  scale.   This  would improve the ability of the body to
shed water, especially on scales of the belly.
 
(2) The growth of lateral projections  (rami)on  these  out-
growths. This would improve increase the surface area of the
projection, so that water droplets would be less  likely  to
strike the body at all.
 
(3) The growth of secondary  lateral  projections  on  these
outgrowths.   (barbules).  still  more efficient at catching
droplets, and due to it's porosity,  strongly  water  repel-
lant.
 
(4) The growth of hooks allowing the structure to interlock.
Now the system is more structurally stable, and still better
at insulation and water repellance. The size of the outgrow-
ing feathers increases at the expense of the scale, which is
no longer needed.
 
Once the feather is available due to evolution to meet  this
need,  it can be fine tuned to serve the purposes of flight.
There you are - a plausible series  of  intermediates,  each
with a selection advantage, and most of which can be experi-
mentally observed.
 
        Regards,
                Max G. Webb
 
_The evolution of feathers_ Jan Dyck, Zoologica Scripta, Vol 14, No 2
pp 137-154, 1985.
 
PS. I am working on your request for an example of his misquoting. You
have 'Adam and Evolution' checked out, yes? I believe he recycles the
Eldredge and Gould PE misquote.

--
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