Re: Tears and 'salt excretion'. Was Re: tears
jamesb@hgu.mrc.ac.uk
18 Oct 1995 15:25:42 GMT
bbur@wpo.nerc.ac.uk (Bill Burnett) wrote:
>
>Yes, well, so they do. On the other hand, if you want to REDUCE internal salt
>levels then you need to INCREASE the concentration of your excretion product.
Well I would definitely like to know if our ancestors had saltier tears
than us. It's a hypothesis that I would like to put forward that they
did, but unfortunately I can't think of anyway to test it. I f anyone can
I'd be delighted. As far as I know only marine animals, humans, elephants
and beavers cry when emotionally disturbed. I don't think that crying
would evolve purely as a social signal. For some reason our ancestors
must have had to flush some toxin out through their tear-ducts. Find an
ape-man fossil with beaver-like teeth and then AAT is stuffed!
You can't
>afford to waste water in a salty environment or you get dehydrated very
>quickly.
You equally can't afford to do this in the savannah mosaic. Coupled with
the fact that we use so much water and salt sweating with our
eccrines, this is a very troublesome area for both theories. Of course I
think AAT is better off here, as both could be explained as salt
excretion mechanisms. But I do admit that getting drinking water in a
marine environment would have been a big problem.
>
all those mammals which don't have dry corneas have
>tear ducts of some description, or am I wrong?
Yes, but in most terrestrial mammals (ie all besides humans and
elephants) tears are only shed in response to chemical irritants or grit
in the eye. Emotional tears in humans are biochemically different too.
>
>Incidentally, do I have to produce a definite rebuttal of the AAT tear
>producing mechanism to convince you? Or would a sufficient alternate
>hypothesis be enough to sow the seeds of doubt?
>
Suggest a suitable toxin that would have been present in the savannah
mosaic that would have led to a new excretion route through the
tear-ducts that later became a social signal and a excretion route for
the break-down products of stress-related chemicals. AAT has a perfect
candidate in the form of salt. But until recently I wasn't aware that
beavers cry to flush out arsenic from tree-bark in their diet, so there
are probably others....
Or you could convince me that elephants don't have a marine ancestor.
Do I really sound like a crackpot scientific creationist?
James Borrett.
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