Re: disadvantageous inter
J. Moore (firstname.lastname@example.org)
Sat, 5 Aug 95 19:16:00 -0500
AD> Alex Duncan (email@example.com) sez:
AD> Pat several times referred to something that I found disturbing. He
AD> suggested that the earliest bipedal hominids would have been
AD> "disadvantageous intermediates", and wouldn+t have been able to survive
AD> in the mosaic/savanna environment. Then, curiously, he cited Dawkins
AD> to support his view.
AD> [explanation of evolution of marginally advantageous intermediates with
AD> example of appendages which eventually become wings deleted]
AD> The point here is that the earliest hominids didn't have to be very
AD> bipeds to take advantage of the open spaces between trees that
AD> at the end of the Miocene. All they had to be able to do was move from
AD> one patch of trees to the next before being gobbled by a predator. If
AD> you can+t imagine them doing that, then the patches of trees in your
AD> are too far apart. Move them closer together and try it again.
Vi> I don't want to make Pat's arguments for him, but his argument is not
Vi> the strawman you have built, because in your argument, you use as an
Vi> example a mutation which is immediately advantageous, rather than
Vi> disadvantageous. Thus you and he are talking at crosspurposes, as he
Vi> clearly has stated that he has no problem with the development of
Vi> characteristics which have marginal advantage.
Then why has Pat repeatedly had a big big problem with the idea of
bipedalism being used by an ancestral population, when there are
plenty of marginal advantages to be had from it. So many in fact
that even creatures not well suited for bipedalism (for instance,
non-brachiators) use it regularly. There are advantages in seeing
further, carrying things, providing more impressive threat
displays... these things have been pointed out repeatedly in this
newsgroup to Pat and sundry and he can still try to claim there were
and are no "marginal advantages"?
Vi> His argument, which you
Vi> skillfully continue to ignore, is that a partially bipedal ape is worse
Vi> off than one fully bipedal or one fully quadrupedal. This is a simple
Vi> sentiment to understand, it is the same one my son voiced to me a month
Vi> or so ago, and the reason for it is also simple. It contains an
Vi> assumption that the bipedal hominids evolved from a quadrupedal
Vi> ancestor, by slowly straightening the hip, lifting the upper body from
Vi> the ground, implying that on the way to full bipedalism they went
Vi> through a stage where the upper body was partially bent forward from the
Vi> hip, in a crouch, which would have been hell on the lower back, and
Vi> awkward for rapid movement.
An assumption that, as has also been repeatedly pointed out, is
incorrect from a couple of perspectives. One is that there is
absolutely no reason whatsoever to believe that hominids went
through some period of hunched over bipedalism -- absolutely
none. Those old posters of progressively less-hunched hominids --
forget them; people have been trying to point out the foolishness
of that assumption for 30 years. Even *if* the common ancestor
between us and African apes was a knuckle-walking-style quadruped,
they would likely stand up as do African apes. Take a look, they
aren't hunched over. End of story.
The other reason is that over the last 20 or so years it has
seemed increasingly likely to many, perhaps most, researchers that
the common ancestor was likely a brachiator, and that both
knuckle-walking-style quadrupedalism *and* bipedalism were derived
traits rather than holdovers from an ancestral past. Although it
must be pointed out that in the case of brachiators, bipedalism
while on the ground is very common and indeed perhaps the predominant
mode of terrestrial locomotion.
Vi> It seems to me that this sentiment is also perfectly valid, and that
Vi> there is no way in hell that we achieved bipedalism by that route. If I
Vi> was a quadruped, it would take one hell of an impetus to get me to go
Vi> around suspending the front half of my body with my lower back muscles
Vi> all the time. No, I believe the source of the problem is that we were
Vi> never quadrupedal. If we were brachiating suspensory feeders, who
Vi> habitually ran along tree branches on our rear legs in upright posture,
Vi> then we would
Vi> already be essentially bipedal by the time we hit the ground. We had
Vi> straightened our backs by hanging from our hands,
Vi> millions of years before we left the trees. The pongids would then be
Vi> the ones who chose to head back toward quadrupedalism, by making use of
Vi> their long arms for locomotion, while we
Vi> found other uses for them.
You've obviously already understood the second point, about
brachiators, but still don't seem to see the first point -- that
even a transition from an African ape-style quadrupedalism would
not entail walking around hunched over.
And the primary point to the thread is still Pat's foolish claim
about the idea of there being a "principle of disadvantageous
intermediates" (or "principle of non- disadvantageous intermediates";
he's tried to claim it both ways). Alex, rather than attempting
to "skillfully continue to ignore" Pat's idea, has simply answered
it, and also shown Pat's continued insistence in attributing this
abomination to Dawkins to be absurd. Pat just doesn't seem to
understand how selection in evolution works. Below is just one of
the many times he's made this misstatement of evolutionary theory,
along with one of my many replies to him pointing out his error.
Pa> Evolution doesn't give you a sub-optimal holiday while you evolve an
Pa> optimal solution - the principle of non-disadvantageous intermediates.
JM> There is no such "principle", as has been pointed out to you many many
JM> many many times so far. The idea that evolution produces "optimal"
JM> behaviors or morphology is a popular misconception, but that's all it
JM> is. Evolution does not force "optimal" results, it selects against
JM> ones that don't work "well enough". The sooner you divorce the words
JM> "optimal" and "evolution" from each other, the closer you'll be to an
JM> understanding of evolutionary principles.
Jim Moore (firstname.lastname@example.org)
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