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Re: birds scales



>On Fri, 8 Dec 1995, Rob Meyerson wrote:
>
>> Then again, it may mean exactly that.  To go out on a limb (and I think
>> I hear it snapping:-), since down is found mostly on chicks, this may=20
>> show that it is a primitive feature (based rather loosely on the=20
>> principle of neoteny). >=20
>> Rob
>>=20
>>=20
> "Principle of Neoteny"?, Neoteny is not a principle of evolution, it is=20
>a process that sometimes occurs in evolution. It results in the=20
>retention of juvenile structures of an=20
>ancestor in the adult of a descendant, more specifically acheiving this=20
>affect by retarding the rate of ontogeny. Therefore the appearance of=20
>down in the juveniles of modern birds is not an example of neoteny. I=20
>think you may have been confusing neoteny with "recapitulation" where the=
=20
>ontogeny of an organism (or a structure of an organism) mirrors the=20
>evolution of that organism (or structure). Ernst Haekel thought that=20
>recapitulation was universal to all organisms and labelled it the=20
>"biogenetic law", this was popular last century but was well out of=20
>favour by the begining of this century. =20

Right.  Neotony was the wrong term; it was recapitulation that I was=
 thinking about.  It may have been out of favor, but I suspect the concept=
 is close to the mark.  The whole idea about the phylums Chordata and=
 Echinodermata being closely related comes from embryology.

With this in mind, I restate my original idea: that since the first feathers=
 to appear on a chick is down (regardless of species), then it can be=
 concluded that the first feathers to appear in the group was down.

Rob

***
"Don't panic!"