Re: Morgab tears /salt

David Froehlich (
Thu, 16 Nov 1995 14:30:31 -0600

On 16 Nov 1995, Thomas Clarke wrote:

> Thus you prefer an explanation which invokes conditions that only
> obtained in the past 10,000 years or less, or with a bit of hand
> waving in the past half a million.
> I don't think anyone has yet commented on my suggestion that there
> is a tendency among PAist to favor explanations for ape/human
> differences that place the changes as late as possible.
> I think you reaction to the stipulated tear composition problem
> illustrates this. Putting aside the AAT explanation, explanations
> could be thought up based on exposure of the eyes to windblown dust
> on the savannah etc that would place the change much further back in time.
> The impulse seems to be to go for the recent explanation.
> Curious in a metascientific way..

As an aside, I think this tendency is real and comes about from the
systematic techniques. Biologists (and I know that I am lumping a lot of
people, some of whom would not appreciate the company) use shared derived
features to determine the relationships among taxa (note the shared
component above). This produces a branching pattern supported by a
series of synapomorphies (clado-masochism terminology). One of the
philosophical underpinnings of this technique is to limit as much as
possible the number of asumptions in the analysis (you do not assume AAS
if that is what you want to demonstrate). One methodologic way to do
this is to optimize the characters (place them on the tree) as far up the
tree as possible (thus emphasizing convergence rather than reversal) so
as to limit the number of incorrect synapomorphies. I think this bleeds
over into some of these more nebulous arguments in a tendency to place
the origin of characters as recently as possible because no evidence for
them exists (no assumption of tears until it can be confirmed). In
effect, since all human populations produce tears and the oldest
divergence that still exists is about 40-60 kya (e.g., aborigines into
Australia) then this is the best guess for the origin of tears. Any
other placement of tears within the hominid tree is an ad hoc assumption.

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