Re: First Family and AAT
H. M. Hubey (hubey@pegasus.montclair.edu)
4 Oct 1995 03:25:42 -0400
Alex Duncan <aduncan@mail.utexas.edu> writes:
>To the best of anyone's knowledge, every tetrapod that ever adopted an
>aquatic existence was a quadruped when it began its aquatic foray (w/ the
>exception of aquatic birds). They all remained quadrupeds or began to
>converge on fish in overall body shape and locomotion. Why would the
>early aquatic hominid have been any different? In other words, if
>becoming a biped is such a wonderful adaptation to an aquatic existence,
>why aren't polar bears, walruses, alligators, mososaurs and otters all
>bipedal?
You are pullling a simple linear extrapolation argument and you
know it.
IF you blow on your hands when it's cold outside, they get warm.
When you blow on your soup, it cools down.
The same action; but not the same result. Even something as simple
as that has complicated solutions. The difference, obviously,
is that the direction of heat flow is dependent on the
temperature gradient so that in one case it strips away the heat
from the soup (actually the boundary layer and the heat too), and
in the other case, it slows down the heat loss (in a way) or
may even add heat to the cold hands.
Instead of a linear one imagine a slightly more complex curve,
say a parabolic one, with a maximum somewhere in the middle,
and via an analogy think of it as representing say a metastable
state. A ball put at the top of this, can fall in either direction
depending on only slight perturbation of its initial velocity.
If an animal already has developed to the point when it's almost
bipedal and doesn't spend 10 My in the water why should look
like the animal which was low on the evolutionary scale and entered
the water almost looking like a lizard??
And besides, bears are more grasping types than,say, dogs, and
certainly more bipedal. I don't know what sea otters look like
when out of the water. As for the lizard type low_scale animals,
why should I (or anyone else) have to explain something that
doesn't need one; if there's so much survival value in using tools
and being grasping animals blah blah how come we still have
animals with hoofs, and why do we still have animals with paws
and why are most animals quadripeds (ignoring the fish and birds)
blah blah...
A (maybe "the") model of evolution that I keep in mind is this:
it has a deterministic component and a random/stochastic one.
A differential equation with random forcing (or perhaps with
random coefficients) might be a good analog. The randomness is
the mutation, so that there's no single solution but a density
function that describes the distribution of a species. (Naturally
this is a short time scales. For long time scales, things get
much more complicated since the paths/trajectories must be able
to split into tree like branches, and I'm not aware of any set
of equations which can even produce this kind of thing even as
an approximation.) So the environmental factors work on changing
the distribution (i.e. some are more fit) and thus to point the
way to the direction of evolution. One way to accomplish this
would be to change the coefficients. (If the coefficients were
constant, then one would have to introduce a forcing function
to point in the direction of evolution.) That explains why
despite the presence of so many brilliant scientists (
mathematicians especially working in this field of genetics etc)
nobody has yet been able to even propose a good mathematical
model of evolution. (Statistical, small sample theory stuff
and correlation-regression type stuff like Dobzhansky's stuff
doesn't count for much. In fact I think he makes serious mistakes,
as do many statisticians when they ignore certain aspects of
problems of this type.)
Anyway, compared to what I think that geneticists, and evolution
theorists have been trying to accomplish, the skeleton
eyeballing is exactly that. I wouldn't have said so if certain
people could have kept themselves from insulting others
needlessly.
--
Regards, Mark
http://www.smns.montclair.edu/~hubey
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