Re: potassium and Tears 2
J. Moore (firstname.lastname@example.org)
Sat, 18 Nov 95 11:56:00 -0500
JM> >*If* emotional tears evolved primarily as an excretion device --
JM> >and I think that is extremely unlikely -- the evidence from these
JM> >terrestrial birds and reptiles would indicate it was for a very dry
JM> >climate rather than any aquatic environment.
Ja> Well the notion that our tear-shedding is adaptive for a very dry
Ja> environment doen't fit very well with our eccrine sweating system, does
Ja> it? Our ancesters MUST have been guzzling lots of fresh-water wherever
Ja> they were, so they can't have been in a very dry environment.
Ja> James Borrett.
I agree that, as my first sentence rather clearly said, it is
extremely unlikely that tears evolved primarily as an excretion
device. This post you're quoting, it should also be noted, was
one I corrected immediately -- you probably saw the post
immediately following it -- to read "tears" rather "emotional
tears". All human tears are hypertonic in regard to potassium,
just as all are isotonic in regard to sodium. I didn't mean to
mention only emotional tears.
It should be noted -- well, actually it shouldn't *have* to be
noted -- that tears are a vital feature in all mammals, not just
humans. This includes animals in the hottest and driest of
deserts; you just can't do without them.
Emotional tears would seem to have likely evolved, as Frey
postulates, to eliminate some substances (they are hypertonic in
emotional tears), none of them being sodium. Their innervation
would suggest that this feature likely did not evolve during the
transition from ape to hominid.
You are also making an assumption which is unsupported by reality;
that an environment which is quite dry has no drinking water
available anywhere, when in fact we can see, from humans, and
chimpanzees for that matter, that environments which are in fact
dry and hot can have sufficient drinking water. This is true even
when drinking water is not carried (for instance, !Kung and
Australian aborigines often do not carry drinking water even in
extremely hot and dry environments). However, sources of drinking
water can be and are carried even by chimpanzees. Our ancestors
could certainly have done the same.
"The Tongo chimpanzees dig for large, water-filled roots (*Clematis*),
which they carry and share like a bottle (Lanjouw, pers. com.) These
inventive practices are clearly responses to the lack of permanent
water" (Wrangham et al., 1994:9, *Chimpanzee Cultures* Edited by
Richard W. Wrangham, W. C. McGrew, Frans B.M. de Waal, and Paul G.
Heltne, with assistance from Linda A. Marquardt. Cambridge, Mass.
and London, England: Harvard University Press).
Jim Moore (email@example.com)
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