Re: Sodium Homeostasis, kidneys, etc.
J. Moore (j#d#.moore@canrem.com)
Fri, 25 Aug 95 17:39:00 -0500
Ad> In article <696763390wnr@desco.demon.co.uk> Elaine Morgan,
Ad> Elaine@desco.demon.co.uk writes:
Ad> >You say the non-skeletal changes I listed - naked skin, fat layer.
Ad> >disturbance of sodium homeostasis, descent of larynx, loss of
Ad> >estrus, etc. - "have all been adequately explained by less far-out
Ad> >hypotheses".
Ad> >
Ad> >That has not been my impression. If you can give me five references,
Ad> >one for each of these characters, offering explanations that you
Ad> >personally find convincing, I will be astounded.
Ad> Well, you asked for it. There is abundant literature available on most
Ad> of this. I will take this in no particular order.
<deleted refs>
Ad> Frankly, I don't know enough about sodium homeostasis to provide
Ad> references for it. I assume it has something to do with sweating.
Ad> Alex Duncan
Ad> Dept. of Anthropology
Ad> University of Texas at Austin
I must say, I find the effrontery of Morgan demanding refs... I
mean, this from a woman whose idea of supporting her claims ranges
from simply making statements without any support, through the
realm of invoking names as support without citing the book or
journal (and certainly not the page numbers), to the ultimate of
selective, and sometimes altered, quoting (again usually without
page numbers). In order to get through life I guess you just have
to enjoy the irony of such a person now demanding refs... ;-)sigh)
Sodium homeostasis has to do with sweating only insofar as
sweating provides a additional load on the system. Sweating and
tears in humans, despite what Morgan would have you believe, are
not regulated outlets for excretion of salt. In mammals, this
part of the system is undertaken by the kidneys. The other end
of the system, you could say, is the mouth, through salt intake.
An excellent source of information on the instinctive basis of
salt appetite in humans and other animals is the very source
Morgan inaccurately used as support for her contrary claim:
*The Hunger for Salt*, by Derek Denton (1982, Springer-Verlag:
Berlin, Heidelberg, New York). I'm presently trying to work up
a post on this work and how badly Morgan misread or misinterpreted
it, but I'm having trouble cutting it down to size.
Suffice it to say that, although Morgan quotes (well, partially
quotes) Denton to support her claim (in *The Scars of Evolution*)
that humans lost their instinctive salt appetite response to
sodium deficit, he in fact says just exactly the opposite.
As just one example, take Denton, pg. 605:
"The hedonic human liking or appetite for salt when it is available,
and independently of any metabolic need, is an evolutionary legacy
of high survival value. It is part of the overall innate
organization dedicated to salt ingestion along with the elements
determining appetite response to sodium deficiency and to the
hormones of the reproductive process."
I've already seen Morgan's 15 Aug response to Gerrit's mention of
kidneys and urine concentration, to whit:
El> Gerrit: Good points about the urine. It would seem to stand to reason
El> that if anything had kidneys they would cope with excess salinity.
El> But in practice it doesn't always apply. The marine creatures that use
El> salt glands or lacrimal glands have kidneys too. Maybe if they get too
El> overloadd with salt it would impair thair capacity to deal with other
El> toxic wastes.
Morgan seems unaware, though I've mentioned it many times now,
that all marine mammals have evolved extremely large and very
heavily lobulated kidneys in response to their saltwater habitat.
Though she insists on the application of convergent evolution when
it comes to sweating on land, claiming that because we don't do as
the "wild ass and the camel" we should throw out the last 30 plus
years of paleoanthropology, she has been reluctant to apply the
same rules to her own theory. She instead has studiously ignored
this example of *actual*, not hypothetical, convergent evolution
by all marine mammals, perhaps because her purported aquatic
ancestor would be the one startling exception.
Her notion, quoted above, that "It would seem to stand to reason
that if anything had kidneys they would cope with excess salinity"
shows yet another glaring blind spot in her reasoning. Mammals
have kidneys that are different from other vertebrates; in
particular, they perform functions that the kidneys of other
vertebrates do not. One of these functions is the regulated
excretion of salt.
Eckert, pg. 393:
"_The Vertebrate Kidney_
"To speak of the vertebrate kidney would be misleading unless we
note that it is organized somewhat differently in different groups
of vertebrates. Comparisons can be made after we first consider
the mammalian kidney. The mammalian kidney performs certain
functions that in lower vertebrates are shared by such organs as
the skin and bladder of amphibians, the gills of fishes, and the
salt glands of birds and reptiles."
It should be noted at this time that another area where Morgan
uses a suspiciously selective application of the concept of
convergent evolution is that she only mentions the salt glands of
marine birds and reptiles, while ignoring the examples of
terrestrial birds and reptiles with salt glands, such as the
ostrich:
Eckert, pg. 415:
"Salt glands have subsequently been described in many species of
birds and reptiles, especially those subjected to the osmotic
stress of a marine or desert environment. These species include
nearly all marine birds, ostriches, the marine iguana, sea snakes,
and marine turtles, as well as many terrestrial reptiles.
Crocodilians have a similar salt-secreting gland in the tongue."
From: 1988 *Animal Physiology: Mechanisms and Adaptations*
(3rd edition) by Roger Eckert (University of California, Los
Angeles), with Chapters 13 and 14 by David Randall (University
of British Columbia), revised in part by George Augustine
(University of Southern California). W.H. Freeman and
Company: New York.
Jim Moore (j#d#.moore@canrem.com)
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