Evidence from endocrine system
Organization: RHBNC, University of London
From: email@example.com (Pnn)
I was reading 'Evolution' by A Franklin Shull (McGraw Hill, 1936) (*),
which goes over the evidence for evolution. (ie, descent with
modification from a common ancestor). Chapter two deals with
comparative anatomy; and one of the points he's trying to make is
that the precise anatomical position of certain glands in vertebrates
is irrelevant to their function, and this is evidence for evolution,
because they can be found in exactly the same anatomical position in
all vertebrates - and why should this be so, if they can be positioned
anywhere in the body?
Specifically, he cites certain parts of the endocrine system - the
thyroid, pituitary and thymus glands - and the reproductive organs
(actually, he talks about the endocrine secretions of the reproductive
organs). He says they're always found in the same position in all
vertebrates ("near the front gill slits", "at the base of the brain",
and "in the neck region or upper part of the chest for several classes
of vertebrates" respectively, for the first three (page 20)), and then
points out that their effects are widely distributed round the body.
He also claims their positioning is irrelevant to their function. How
does he know this? Well, from page 20:
"The conclusion that these organs might be elsewhere and still serve
the same purpose is not mere conjecture. It has been proved by
grafting them into strange situations, or by introducing their
secretions artificially at other points."
Does anyone know where I can read up more on these experiments? IMO,
finding details of anatomy that could be different but aren't makes
for some pretty good evidence, and this is the only book I've come
across that addresses this point.
There's also the problem that what he's saying seems slightly dubious.
Isn't there a feedback mechanism built into the endocrine system, that
it makes sense that some glands (the pituitary - isn't that influenced
by the hypothalamus?) be where they are?
email, please: I'll won't be able to access the Net for much longer.
(*) why'm I reading a book so long outdated? Because I've got a
weird library, whose sole book with a more than elementary modern
treatment of the biological evidence for evolution seems to be 'The
Science of Evolution'/William D Stansfield, that's why. Maybe I
haven't looked hard enough.
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