Re: tears

David Froehlich (
Sat, 21 Oct 1995 16:47:19 -0500

On 20 Oct 1995, H. M. Hubey wrote:

> David Froehlich <> writes:
> >Have you ever heard of kidneys? These seem to be much better at getting
> >rid of excess salt. Isotonic tears are not an efficient method of
> >loosing salt, urine is.
> So what? We're discussing something else.

No we were not, you were talking about using tears as a salt excretion
mechanism and I asked why should any organism bother since kidneys are a
much more effective mechanism to regulate sal balance

> Besides which, if you are living in a marine
> >habitat where is this fresh water coming from?
> 1) I didn't say that they never drank fresh water.

But given a use of tears as a salt excretion mechanism, not only would
you need some water, you would need lots. If you are implying that they
needed a mechanism to excrete salt (in other words, highly concentrated
tears that we have since lost) then you are indeed implying that they
drink salt water (they need to get rid of it).

> 2) Even if they had adapted to salt water, the kidneys could have
> changed over time, and probably faster than bones.

How would you test this? If it has left no trace then you have no evidence!

> 3) It could have been an estuary or a lake, maybe even a swamp.

This is where the crocs are, and osmotically, the problem is just the
reverse, now you need to retain salt and get rid of water (in which case,
isotonic tears are to concentrated).

> And we could ask the same question for the grassland dwellers.
> OF course, they'd need to hang around water. The question is
> one of degree.

How much? You are the person that wants to assign numbers to everything,
how much time would the putative AAS hominid spend in water? You can't
have it both ways. Either these are terrestrial animals drinking water
or they are aquatic and only getting out of water occaisionally
(otherwise why would their morphology change?).

> >So what? Producing isotonic tears as a salt excretion mechanism only
> >works if you have voluminous amounts of fresh water. The energetics of
> >the situation (you would have to expend a lot more energy to expel salt
> >in this manner than with concentrated mechanisms such as using the
> >kidneys) would seem to indicate that the use of isotonic tears is
> >extremely unlikely.
> It's unlikely that they didn't have kidneys! They urinated like
> every other animal. The question is not about that so don't twist
> it out of shape into a straw man. Just because the complete
> answer is not there doesn't mean that there isn't something
> there that's strange an unusual. We still have the problem
> of tears that seems to be associated with emotion and also
> with animals that seem to have water affinities. Can we call
> this "affinity" aquatic or semi-aquatic and get it over with
> instead of fighting over wading, dunking, splashing...

No we cant call it an "affinity" or aquatic or semi-aquatic because in
any form of AAS there must have been sufficient time for the organisms to
aquire bipedality in the water.

> >organism out (ie an increase in the length of the loop of henley).
> >Interestingly, there is no evidence of this change. I wonder what AAS
> >proponents make of this anotomical structure? To my eyes it seems to
> >falsify the AAS position (at least for AAS in seawater). Any comments?
> Sure. The extra salt due to salt water could have been the
> reason for the tears. You already have animals that have
> working kidneys, and you might have a marginal problem with
> salt. The weeping could have been the extra little thing needed
> to keep the salt balance. The habitat could have been an
> estuary or something like that periodically flooded with sea water.
> I don't know how one would go about forcing animals to live in
> salt water and then studying the effects of the salt in the water.

You just do not get it do you? if the tears are isotonic then any salt
you get rid of is not going to do you any good because it doesn't change
the internal chemistry. Why bother if you have sufficient fresh water to
drink (because the real problem is not to much salt in the body when you
are in brackish or salt water, it is to little water in the body because
it is always moving to the hyperosmotic solution (the sea water).

> I suppose we could look at sea otters, polar bears, penguins and

Funny thing? sea otters have better kidneys than humans, polar bears and
seaotters also have skin oils that waterproof the fur, polar bears and
penguins dive into polar waters that are less saline than ocean
waters at the equator, finally ocean birds that have to drink sea water
(fulmars and albotrosses etc) have salt excretion glands on their beaks
where they excrete fluid many times more concentrated than their body

David J. Froehlich Phone: 512-471-6088
Vertebrate Paleontology Laboratory Fax: 512-471-5973
J.J. Pickle Research Campus
The University of Texas, Austin, Texas 78712