square-cube law

6 Jan 1997 17:18:41 GMT

I know this isn't quite on topic but since paleontology often makes
use of knowledge about skeletons I thought I would ask... does anyone
here know what how tall/heavy a bipedal hominid could get before the
square-cube law would provide limits.

Those limits would be based on the fact that the mass a leg
has to hold up increases as the cube of the height of the person,
while the strength of the leg bone only increases as the square
(i.e. the cross-section of the leg).

My thoughts on the matter:

To walk/run on two limbs, an animal needs at least three points
of contact per foot (maybe five, I have read that humans can't run without
their outer toes). There must be some flexibility as to how weight
is distributed among those points of contact, and the points must be fairly
widely spread out front to back.

This rules out using a four legged beast such as an elephant as
a model (and then dividing by two).

There were bipedal (sort of) dinosaurs, but (almost?) all of them
had tails and substantially different walking/running modes that (to my
untrained eye/brain) would put much strain on muscles rather than on the
bones. I guess the strain would be more spread out along the bone?
In any case the strain would be different than it is in humans.

Emus and Ostriches have different gaits than humans but somewhat
closer, OTOH what is the largest an Emu gets?

The tallest human was around 9 foot? 7'X" seems fairly common
in the NBA, I don't recall anybody at 8 ft. Is that pure genetics, or
are there 8ft folks out there who don't have the leg bone strength to
play basketball?



(I tried to post this earlier but never saw it come up, if this is
a repeat, my apologies)
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