Here are three replies which were sent to me directly.


Hello Liming,

About your comment on the wheel - there are actually wheel-like structures
in micro-organisms (no particular ones come to mind). I remember reading
about one that has a fagella (tail) attached to it and this tail rotates
by a wheel-like mechanism - actually, imagine the tail joined through a
molecular ball bearing.

As for larger animals, wheels may be too complex to evolve - there can be
no physical connection unless you "unwind" your tendons and blood vessels
that connect to the wheel-limb. Otherwise, your tendons/vessels will just
wrap around the wheel like a plastic bag on a shopping cart and the wheel
stops moving... You need connections to send/recieve signals and
nutrients, both of which may also move through diffusion, but for larger
animals the amount of surface area that this would require will probably
be way too much.

Did I say too complex to evolve? I know, I know, the current systems are
complex enough, and I can't really justify why the wheeled structure has
not evolved, but I just wanted to share a few thoughts.


Jerry Hu
Musculoskeletal Bioengineering Laboratory
Rice University
Department of Bioengineering - MS 142
P.O. Box 1892, Houston, Texas 77251-1892
Tel: (713) 348-6393
Fax: (713) 348-5877

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I saw somewhere that there are some baboons in Africa that tumble or
cartwheel down hills. It's not a wheel but it's along those lines.

If you had an appendage that served the same purpose as a wheel, how would
it continue to rotate without getting ligaments, tendons, and muscles all
tangled up?

Bryan St. Laurent

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I assume a wheel is different to rolling the whole organism. If that
is the case then reasons why the wheel has not developed in the
animal kingdom could include:
1. All wheeled systems have the rotatory component not connected to
the main framework. This would cause problems for a) transmission of
feedback from the wheel. b) how the rotation force is transmitted to
the wheel - assuming there is a drive wheel otherwise other limbs
could do the driving i.e like a wheel chair.
c.) the ability to provide a safe protection of the skin interface at
the 'universal joint' which would also meet the various needs for
stability, low friction, ability to rotate..

2. Finally, if the wheel developed then that would mean my lectures
on stretch shortening cycles would have to be changed to stepper
motor or cam shaft development.. .. phew.
Garry T Allison Associate Professor of Physiotherapy
The Centre for Musculoskeletal Studies
Department of Surgery, The University of Western Australia.
Level 2 Medical Research Foundation Building
Rear 50 Murray Street
Perth Western Australia 6000.
ph: (618) 9224 0219
Fax (618) 9224 0204

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