Re: AAT Theory

H. M. Hubey (
27 Sep 1995 14:26:37 -0400 (David L Burkhead ) writes:

> A) Nobody ever said that humans were adapted to running speed.
>Thus, comparing comparing it to claims of "streamlining" is a

I guess then there must be a reason for the size of humans to
be what they are.

> B) All "higher" primates, particularly the great apes, adopt
>varying degrees of bipedal locomotion. Chimps and gorillas sometimes
>walk bipedally. Gibbons _always_ do so on the ground.

OK, so bipedalism is more or less a continuous variable and
there are degrees of bipedalism.

> C) That _you_ cannot envision a series of gradual improvements in
>bipedal locomotion, in an animal that already _had_ the capability to
>use it at least some of the time, does not mean that I am so limited.
>Arguments from ignorance are rarely convincing. That's why they are a
>logical fallacy.

If gradual improvements were the norm then that would put
you in opposition to the latest/greatest addition to evolution,
that of punctuated equilibrium. Then we'd have lots of fossils
with legs getting longer and longer, and we need a reason for
that too.

> You betray your limited knowledge here. (Well, my knowledge is
>limited too, as is anybody's, but, in this subject, it appears to be a
>bit less limited.) There is no "suddenly" involved. We have animals

Like everything else in this field, there's no number attached to
"suddenly"; and there's no number attached to "bipedal" either.

And changing from egg-laying to keeping it inside the body is
a sudden change, compared to the time scales of other phenomena
of this type.

>mother than just fertilized eggs. We see animals whose eggs have
>thinner shells than others. We see animals where they dispense with
>the shell entirely and carry the embryo externally (albeit in a
>"pouch" in the cases I can think of offhand).

Well, it seems the word "sudden" needs a "scientific definition" !

> Again with the streamlined. That's a _claim_, not a "fact."

Compared to physics, all of evolution is claim, not fact. Compared
to mathematics, there's no such thing as proof in this field, just
lots of evidence waiting to be toted up in various ways.

>upright wading ape. Go look up turbulent vs laminar flow separation
>drag in bluff bodies. (This kind of thing is one of the reasons the
>"obvious" is so often wrong.)

I could look it up why not just give us the references and make
it easy for us. At what speeds in water does the Reynolds number
hit the turbulent/laminar boundary? I do agree that the obvious
in fluids sometimes is not right but I'd have to see actual
experimental results before I'd be convinced that a hairy body
has less drag than a smooth one.

>streamlining as australopithecines, then regained it again as homo
>sapiens, we must have gained it for other reasons. If we gained it

You keep doing this while ignoring simple things like the fact that
we haven't even been able to clearly delineate what "streamlined"
means. It seems that we are now arguing over the same kind of
thing as whether given Neandertal skulls vs Cro-magnon they were
the same biological species. The evidence is that the bones are
not capable (from what we now know) of resolving this problem.

Now we are arguing about which of the ancestors were more or
less streamlined without even being able to give a number to
the level of streamlining of the animals.

Besides, if the streamlining was due to the water and if one
of its side-effects was upright posture there'd be no reason
why it would be lost upon leaving the water.

We'd have the same scenario of the digit-lenghtening was
occuring simultaneously with webbing for an aquatic life
style, and if the animal left the water, the webbing would
presumably be lost but the longer digits being useful for
grasping would/could stay.

> Why invoke an aquatic phase for long digits since _all_ the apes,
>and every monkey species I know already has them? Once again, you
>cannot invoke an aquatic phase to "explain" traits that developed
>elsewhere and retain any credibility whatsoever.

Maybe there was an aquatic phase even earlier and for some
primates it stopped when they left it to climb the trees and
the others just stayed in that environment longer.

Furthermore, the
>chimp/ape foot, with its long toes and separated first digit is a much
>better canditate for aquatic propulsion than the hominid/human foot.
>This would then seem to contradict your hypothesis.

How. It makes it even better.

The grasping appendages developed in water. Apes left the water
earlier and adapted to trees. Humans hung around longer and in
the soft sandy beaches developed feet more like camels. Toes could
have become shorter (and maybe lose some webbing) because of the
movement to land.

> Once again, you are making assumptions about "streamlining" that
>are just plain not justified. And the more assumptions you keep
>piling on the case, the less tenable it becomes.

The dividing line between assumption and theory is blurry in this
field. There's no laboratory where the variables can be kept
controlled, and the whole picture (i.e. the theory) itself may
be considered to be a large number of assumptions. Surely this
is different than both math and physics, and more difficult than
economics because of the time scales involved.

> Adaptations for wading are not adaptations for swimming are not
>adaptations for diving are not adaptations for ducking. And the Cd of
>the body posture for one activity will _not_ be the same as the Cd for
>another. Aren't _you_ the one suggesting taking a few fluid mechanics
>courses? Why not take your own advice?

We're not designing speed boats :-).. Yes, for a perfect diver
it would have to be designed like a needle or a nail :-).. For
swimming having propellers would certainly help :-)..

Those that swim, also wade and dive. You're really blowing
up little things out of proportion.

> Also, wading is not just how the so-called aquatic ape "got
>started." It's supposed to have been their primary activity for a
>million+ years. It's supposed to be a critical factor in why we are
>bipedal, and you just can't get that from swimming--the adaptations
>are all wrong. Of course, they're all wrong for wading too, but
>that's another story.

Yes, we already went through this. Yes, staying in the water and
trying to escape land predators would have favored long legs,
and being tall so that they could "wade" (swim, dive) away from
the predators.


Regards, Mark