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RE: Juvenile characteristics (was) MORE FEATHERS & NEKKID MAMMALS
and Wayne responded>
> I believe "atavism" is the word you want. "Atavistic" (primitive)
> characteristics do show up during embryonic development (..) because
> they are indeed coded into the genetic material. Generally the
> characteristics we now consider primitive (..) show up only briefly,
> if at all, and are then reabsorbed -- like the gills and tails you
> mention. Occasionally the genes that are supposed to suppress these
> developments malfunction, and we get Jojo, or babies with tails, or
> hens with teeth.
>> Is development (and loss) of such characteristics AFTER
>> birth/hatching the same sort of thing? Human babies are frequently
>> born with hair over every surface of the body which is lost shortly
>> after birth
>Since, as you point out, this is frequent, I'd be rather hard pressed
>to call this specifically "primitive" -- it's still with us, even if
>it serves no function that we can presently determine.
True-I called it primitive as it retains the trait from an earlier form.
But that still doesn't answer the question of is it the same thing
(recapitulated phylogeny etc) if the reabsorption happens AFTER
>I thought I remembered reading somewhere that the hoatzin's juvenile
>fingers were actually used for climbing around for a while before
>they were reabsorbed -- of course, this would be before the wings
>prepared themselves for flight. (I could be wrong about this --
>somebody please correct me if I am.) If this is indeed the case,
>then these atavistic fingers actually would serve a useful function,
>and have justified their persistence.
So maybe they got a use for them that might justify a retention of them
and maybe Jojo pays for college by having a hairy face and a contract
with Head and Shoulders.;]
I think what I'm asking here is- can the juvenile fingers of a Hoatzin or
Marsh chick simply be a case of a primitive trait (certainly retained
from an earlier form) a suppressor gene that is functional in most other
birds simply NOT working in a timely fashion in birds with juvenile
So maybe all birds might be able to grow fingers as juveniles if their
supressor gene is turned off?
Might it be a case where an enzyme or hormane finally triggers the
reabsorption of the fingers at a certain stage of growth? Rather than at
an embryonic stage? I know when humans NOW have the Jojo trait, they can
be treated with hormones so that they appear normal (I don't know it this
is a permanent resolution to the hair problem or if this treatment is
recurring for their lifetime), so could a Hoatzin be treated with
something similar to remove the fingers earlier than it might normally?