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Here is a continuation of our discussion - all messages which
I received during this weekend.
Krystyna Gielo-Perczak, Co-moderator Biomch-L
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From: Robert B. Eckhardt
To: Thomas Greiner and other colleagues
Dear Tom et al.,
I like your answer overall. It is correct on the structural and functional
homologies and the evolutionary pathways thereto.
There is perhaps some reason to reconsider the last part of the answer:
[Humans with "short" feet are evolutionary hold overs from the necessity of
powerful
locomotion in their arboreal (tree climbing) ancestors.]
Two points:
1. Our most immediate tree climbing ancestors were anthropoid apes
generally similar to chimpanzees and orangutans of today (a good actual
fossil antecedent exists in the form of the partial skeleton of CLl-18000
from Spain circa 9-10 million years before present). Details of means and
ranges aside, these animals are roughly comparable to extant humans in body
mass.
These animals were referred to graphically by our Victorian
anatomist/morphologist intellectual counterparts as "quadrumana" -- that
is, as "four-handed," because they could grasp objects, including branches,
with all four appendages. In the trees they do just that, thereby
spreading their weight (technically, mass) over four limbs, while in
contrast terrestrial humans of necessity transmit all of our weight through
the hind limb only. On those grounds it would seem that arguing for human
"short-footedness" as an evolutionary holdover is unsupported (no pun
intended). I think that if the point were investigated in detail (i.e.
this is a hypothesis, not a certainty), we would find that both absolutely
and per unit mass, humans actually are shorter-footed than might be
predicted from the anatomical characteristics of their anthropoid
predecessors, if isometric scaling of body mass and foot length were the
only factor affecting foot size.
2. Humans (using that term broadly in an evolutionary sense) have been
terrestrial for roughly 6 to 8 milion years (my estimate). Over that
timespan, numerous features of the trunk and limbs -- forelimb and hind
limb segmental and overall lingths, trunk proportions including numbers of
lumbar vertebrae, etc. -- have been modified substantialy. Against that
background, adjustment of foot length (relatively and/or absolutely) would
not have provided much of a problem evolutionarily. Again, the "holdover"
argument is not persuasive in this context.
Some of these points are open to direct test. Let me know what you think.
Bob
Robert B. Eckhardt
Professor of Developmental Genetics & Evolutionary Morphology
Department of Kinesiology
Penn State
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From: Rodger Kram
Sorry to chime in late after lurking for a week or more but....
Although vertebrates are bilaterally symmetric in form, most all
quadrupeds (cheetahs, horses, greyhounds) use an asymmetric gait
(i.e. rotatory or transverse gallop) at their fastest speeds.
Asymmetry is not inherently bad/slow.
Rodger Kram
Univ. of Colorado
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From: "Dr. Chris Kirtley"
Dear all,
I confess to being a little disappointed with the suggested reasons as
to why birds' legs are bent the wrong way. Here they are:
Animals with long feet adapted more for speed than power/stability
(Greiner, de Lussanet, Ferris)
No idea (Johnson)
Pecking for food (Mcfadyen)
Whilst, I suppose the first answer is more democratically correct, I am
going to award the prize to Brad Mcfadyen, whose lateral thinking came
up with a solution just as plausible.
Although of course we have to agree with Wes Johnson's critique of
Aristotle's methods, I do think it is humbling that, despite our modern
Baconian methods (Feynman, I would contend, was rather a late-comer in
the development of Scientific Method) we still don't have answers to
these questions which he raised 2350 years ago.
Many thanks for your replies, and stand by for the next quiz...
Chris
--
Dr. Chris Kirtley MD PhD
-----------------------------------------------------------------------
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---------------------------------------------------------------
I received during this weekend.
Krystyna Gielo-Perczak, Co-moderator Biomch-L
----------------------------------------------------------------------------
------
From: Robert B. Eckhardt
To: Thomas Greiner and other colleagues
Dear Tom et al.,
I like your answer overall. It is correct on the structural and functional
homologies and the evolutionary pathways thereto.
There is perhaps some reason to reconsider the last part of the answer:
[Humans with "short" feet are evolutionary hold overs from the necessity of
powerful
locomotion in their arboreal (tree climbing) ancestors.]
Two points:
1. Our most immediate tree climbing ancestors were anthropoid apes
generally similar to chimpanzees and orangutans of today (a good actual
fossil antecedent exists in the form of the partial skeleton of CLl-18000
from Spain circa 9-10 million years before present). Details of means and
ranges aside, these animals are roughly comparable to extant humans in body
mass.
These animals were referred to graphically by our Victorian
anatomist/morphologist intellectual counterparts as "quadrumana" -- that
is, as "four-handed," because they could grasp objects, including branches,
with all four appendages. In the trees they do just that, thereby
spreading their weight (technically, mass) over four limbs, while in
contrast terrestrial humans of necessity transmit all of our weight through
the hind limb only. On those grounds it would seem that arguing for human
"short-footedness" as an evolutionary holdover is unsupported (no pun
intended). I think that if the point were investigated in detail (i.e.
this is a hypothesis, not a certainty), we would find that both absolutely
and per unit mass, humans actually are shorter-footed than might be
predicted from the anatomical characteristics of their anthropoid
predecessors, if isometric scaling of body mass and foot length were the
only factor affecting foot size.
2. Humans (using that term broadly in an evolutionary sense) have been
terrestrial for roughly 6 to 8 milion years (my estimate). Over that
timespan, numerous features of the trunk and limbs -- forelimb and hind
limb segmental and overall lingths, trunk proportions including numbers of
lumbar vertebrae, etc. -- have been modified substantialy. Against that
background, adjustment of foot length (relatively and/or absolutely) would
not have provided much of a problem evolutionarily. Again, the "holdover"
argument is not persuasive in this context.
Some of these points are open to direct test. Let me know what you think.
Bob
Robert B. Eckhardt
Professor of Developmental Genetics & Evolutionary Morphology
Department of Kinesiology
Penn State
----------------------------------------------------------------
From: Rodger Kram
Sorry to chime in late after lurking for a week or more but....
Although vertebrates are bilaterally symmetric in form, most all
quadrupeds (cheetahs, horses, greyhounds) use an asymmetric gait
(i.e. rotatory or transverse gallop) at their fastest speeds.
Asymmetry is not inherently bad/slow.
Rodger Kram
Univ. of Colorado
--------------------------------------------------------------
From: "Dr. Chris Kirtley"
Dear all,
I confess to being a little disappointed with the suggested reasons as
to why birds' legs are bent the wrong way. Here they are:
Animals with long feet adapted more for speed than power/stability
(Greiner, de Lussanet, Ferris)
No idea (Johnson)
Pecking for food (Mcfadyen)
Whilst, I suppose the first answer is more democratically correct, I am
going to award the prize to Brad Mcfadyen, whose lateral thinking came
up with a solution just as plausible.
Although of course we have to agree with Wes Johnson's critique of
Aristotle's methods, I do think it is humbling that, despite our modern
Baconian methods (Feynman, I would contend, was rather a late-comer in
the development of Scientific Method) we still don't have answers to
these questions which he raised 2350 years ago.
Many thanks for your replies, and stand by for the next quiz...
Chris
--
Dr. Chris Kirtley MD PhD
-----------------------------------------------------------------------
---------------------------------------------------------------
To unsubscribe send SIGNOFF BIOMCH-L to LISTSERV@nic.surfnet.nl
For information and archives: http://isb.ri.ccf.org/biomch-l
---------------------------------------------------------------