Re: AAT Theory
David L Burkhead (r3dlb1@dax.cc.uakron.edu)
28 Sep 1995 14:33:33 GMT
In article <hubey.812224816@pegasus.montclair.edu> hubey@pegasus.montclair.edu (H. M. Hubey) writes:
>r3dlb1@dax.cc.uakron.edu (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
>>non-sequitor.
>
>I guess then there must be a reason for the size of humans to
>be what they are.
Actually, no. Not one reason. Rather a whole suite of forces
that, in toto, combined to drive human evolution to its current state.
There are several things humans are _very_ good at. We are tool
users. All the hominids of which I have knowledge were also tool
users. We are social animals (allowing us to gang up on
predators--when you can see those predators coming and when they can
be intimidated by numbers in potential prey, both traits lacking in
crocodylians.) We are superb at doing extended exertion under high
thermal stress. There is a trade for this last one, of course, in
that we expend a lot of water for that. However, with the
availability of waterholes (which _are_ found on the savannah) we can
function effectively at times of the day when most other animals have
to rest.
>
>
>> 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.
"Gradual" is in the eye of the beholder. "Overnight" in
evolutionary terms (a la "punctuated equilibrium") is still on the
scale of thousands to tens of thousands to hundreds of thousands of
years.
Also, you might want to take a look at changes to
Australopithecines, homo habilis, homo erectus, etc. over time. The
changes in body proportions and such are far more progressive and
gradual than popularizations of human evolution might have you think.
And the fossil record _is_ sketchy. It will always be sketchy since
only by the most exceptional of circumstances do animals leave fossil
records in the first place. So two finds, half a million years apart,
would show the changes of that half a million years, which might seem
a substantial, "sudden" change. That we don't see the intermediate
steps doesn't mean that they weren't there.
>
>> 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.
Such as? What time scale is involved? Note that small mammals
coexisted with dinosaurs. I don't know whether they lay eggs or gave
birth to live young (and doubt anybody does--except possibly in a few
isolated cases), but even if they were egglayers that's 65 _million_
years, at least, to develop bearing live young. "Suddenly"? You have
a definition of the word that's awfully generous even on geological
time scales.
>
>>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" !
Well, I don't know _any_ definition, scientific or otherwise,
that considers "sudden" to apply to processes that took tens of
millions of years. That's a long time even on geologic scales.
>
>
>> 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.
You keep citing that word "physics" as if it were some mantra.
If you are making a claim that just is not supported by any data
you've presented. If you want to claim that humans are more
"streamlined" than apes, then back it up: show me your CFD results,
or your measured CD vs Reynold's number tests.
>
>>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.
Experimentally, transitional Re is about 500,000. For a human
sized person _wading_ in water (upright posture), that equates to a
speed of 4.8 m/s. That's about 11 MPH. It's also half again as fast
as the fastest Olympic swimmers in the 100m sprint, and people can
swim faster then they can wade in chest deep water (a depth essential
to the aquatic ape thesis).
As for "experimental results" try a golf course: rough surfaced
golf balls (dimpled) fly farther than smooth surfaced golf balls. The
value of a rough surfaces when the main drag sourse is flow separation
is something that's taught in a first semester fluid mechanics course.
You might try those fluid mechanics courses you recommended to _me_
yourself.
>
>
>>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.
Well, since the "streamlining" claim is _yours_ why don't you
clearly delineate it. If you _can't_ delineate it, then your claim is
just plain too vague to stand.
And once again, you introduce a non-sequitor. Since streamlining
is a function of shape, and since shape _is_ something we can largely
determine from bone structure, it most certainly _can_ be resolved.
>
>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.
Then why did you make the claim? The claim of humans being more
streamlined than apes is _yours_. If you can't assign a value to the
level of streamlining, how can you make the claim that one value is
greater than another?
In fact, that's the whole point: I haven't claimed that humans
are more or less streamlined than apes. I've merely questioned _your_
claim that they were. (At least not intentionally have I made the
claim.)
>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.
Are you being intentionally obtuse? Our ancestors, those who
would have _had_ to live _after_ any aquatic phase, did _not_ have
the traits you seem to be citing as evidence of "streamlining" (coming
down, basically, to our being longer and thinner than apes). If we
_did_ develop them in the water, then we most certainly _did_ lose
them later since A. afarensis and A. africanus, and H. Habilis most
certainly didn't have them. And if we "re developed" them later for
other reasons (and we have--we are certainly taller and thinner than
these ancestral species), then there is no need to invoke a water
lifestyle to explain traits that did not appear until millions of
years after we left the water.
If we didn't _lose_ them after leaving the water, then we never
_had_ them. In either case, they are _not_ evidence for any such
water phase.
>
>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.
Read below: Long digits developed prior to anything that could
conceivably be this "aquatic ape." They exist in _every_ primate
species of which I am aware--including monkeys, apes, lemurs,
tarsiers, etc.
>
>> 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.
To do that, you'd have to go back to before there were apes of
any kind, indeed, you'd have to go back to the common ancestor of all
primates at least. Thus, you are no longer talking about an "aquatic
ape."
OTOH, if you go back far enough, you'll find yourself in
agreement with most paleontologists. After all, we _do_ have an
aquatic ancestor in Icthyostega or one of its relatives.
>
>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.
And tarsiers and lemurs? They're primates too, of a type
antecedal to both apes and hominids. Yet they, too, have the long
toes and grasping appendages of apes and humans. Where do they fit in
your little just-so story? And how about old-world and new-world
monkeys? They _also_ have those grasping appendages and long digits.
That puts your aquatic animal back before the common ancestor for
_both continents_. As I said, if that's what you are saying, then we
are no longer talking about an "aquatic ape." And we are most
certainly no longer talking anthropology.
>> 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.
What are you trying to pull here? That anthropology can be fuzzy
(and I would be the _last_ to dispute that, although others might),
does _not_ give you license to use fuzzy _physics_. And your claim of
streamlining is a _physics_ claim. It has to do with the fluid
dynamics of bluff bodies (such as a wading human/hominid). The
answers there cannot just be arm-waved away.
>> 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.
No. You are armwaving away serious flaws with your theory.
_You_ are the one who keeps citing "streamlining." _You_ are the one
who neglects to define precisely what you mean by that claim. _You_
are the one who keeps trying to justify fuzzy physics by invoking
fuzzy anthropology. All I'm doing is calling you on it.
>
>> 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.
Except that the species lying between humans and apes were short.
They were not tall. Thus, either they never did get tall in the
water, or they lost that tallness on leaving it. In either case, our
current height is no evidence of that aquatic phase. Also, animals
that escape predators by fleeing into the water, do _not_ adopt a
wading posture. I can't think of _one_ that does so. Also, in the
areas where hominids evolved, the water is someplace one generally
doesn't want to spend a lot of time if your goal is escaping
predators. Crocodylians are, and have been as long as there have been
hominids, endemic to that part of the world. Often the first sign one
is there is your buddy going under. They don't respond to threats, so
the only way to defend against it is to kill it or to flee. And the
only place to flee is, you guessed it, land.
Land predators, OTOH, _could_ be handled by hominids in exactly
the same way they are handled by chimpanzees today--by ganging up on
the poor predator and throwing sticks and rocks at it until _it_
flees. I've seen chimps doing this more than once. Obviously, then,
animals about the same size and brainpower of our hominid ancestors
are capable of dealing with land predators. There is no evidence that
they would be able to deal with aquatic predators.
David L. Burkhead
r3dlb1@dax.cc.uakron.edu
d.l.burk@ix.netcom.com
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