Re: disadvantageous intermediates?
pete (VINCENT@REG.TRIUMF.CA)
4 Aug 1995 10:38:45 GMT
Alex Duncan (aduncan@mail.utexas.edu) sez:
`We havent heard anything from Pat Dooley for a while. Did we chase him
`off?
`Pat several times referred to something that I found disturbing. He
`suggested that the earliest bipedal hominids would have been
`disadvantageous intermediates, and wouldnt have been able to survive
`in the mosaic/savanna environment. Then, curiously, he cited Dawkins to
`support his view.
[explanation of evolution of marginally advantageous intermediates
with example of appendages which eventually become wings deleted]
(by the way, whatever character you're using for an apostrophe, it's
causing deep confusion to my editor, and showing up as 9's in my
newsreader)
`The point here is that the earliest hominids didnt have to be very good
`bipeds to take advantage of the open spaces between trees that developed
`at the end of the Miocene. All they had to be able to do was move from
`one patch of trees to the next before being gobbled by a predator. If
`you cant imagine them doing that, then the patches of trees in your head
`are too far apart. Move them closer together and try it again.
I don't want to make Pat's arguments for him, but his argument is
not the strawman you have built, because in your argument, you use
as an example a mutation which is immediately advantageous, rather
than disadvantageous. Thus you and he are talking at crosspurposes,
as he clearly has stated that he has no problem with the development
of characteristics which have marginal advantage. His argument,
which you skillfully continue to ignore, is that a partially
bipedal ape is worse off than one fully bipedal or one fully
quadrupedal. This is a simple sentiment to understand, it is the
same one my son voiced to me a month or so ago, and the reason for
it is also simple. It contains an assumption that the bipedal
hominids evolved from a quadrupedal ancestor, by slowly straightening
the hip, lifting the upper body from the ground, implying that
on the way to full bipedalism they went through a stage where
the upper body was partially bent forward from the hip, in a
crouch, which would have been hell on the lower back, and awkward
for rapid movement.
It seems to me that this sentiment is also perfectly valid, and
that there is no way in hell that we achieved bipedalism by that
route. If I was a quadruped, it would take one hell of an impetus
to get me to go around suspending the front half of my body with
my lower back muscles all the time. No, I believe the source
of the problem is that we were never quadrupedal. If we were
brachiating suspensory feeders, who habitually ran along tree
branches on our rear legs in upright posture, then we would
already be essentially bipedal by the time we hit the ground.
We had straightened our backs by hanging from our hands,
millions of years before we left the trees. The pongids would
then be the ones who chose to head back toward quadrupedalism,
by making use of their long arms for locomotion, while we
found other uses for them.
--
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vincent@triumf.ca <== faster % Pete Vincent
vincent@freenet.vancouver.bc.ca % Disclaimer: all I know I
% learned from reading Usenet.
|