Re: Tears and 'salt excretion'. Was Re: tears

Thu, 19 Oct 1995 07:55:31 GMT

In article <46369m$> writes:
>Subject: Re: Tears and 'salt excretion'. Was Re: tears
>Date: 18 Oct 1995 15:25:42 GMT

> (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.

Why not? We have evolved a remarkable repertoire of facial signals by which we
display our emotional state. Given that tears are available to keep the eyes
moist, it seems not impossible for tears to have been recruited for signalling

>For some reason our ancestors
>must have had to flush some toxin out through their tear-ducts.

Why MUST they? This is an unjustifieable deduction.

> 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

>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....

We don't have to suggest a "suitable toxin" , your idea for this role for
tears seems to be uneccessary.

>Or you could convince me that elephants don't have a marine ancestor.

>Do I really sound like a crackpot scientific creationist?

No, because you are not disputing the existence of evolution by natural
selection. But I think many of your arguments are seriously flawed.

Robert Saunders