On 09/08/2013 23:14, David Hare-Scott wrote:
Jymesion wrote:
On Fri, 09 Aug 2013 09:29:41 +0100, Jeff Layman
wrote:

It's interesting that nature didn't come up with the wheel, one of
the most energy-efficient ways of moving around (or did I read a few
years ago that there was some strange organism which could move like
a wheel?

That's a question which comes up frequently.

There's an interesting paper on it at:
http://www.jstor.org/discover/10.230... 102539587717

The current consensus is that the main problem with biological wheels
is blood flow, but this author addresses a different argument.

I haven't seen this article, I will have a look time permitting. One reason
a wheel is not much use for transport biologically is that they require
roads to be efficient. Legs are much better on broken ground and can be
adapted to climbing, become wings, flippers etc.

Well, ATVs get around ok. Even caterpillar tracks are just a form of
elongated wheel. They have little problem with rough ground. Just look
at the moon and Mars rovers. True, they don't move far, but they can
get around. And remember there are vast tracts of flat lands here on
Earth - the prairies, steppes, savannah, etc on which wheels would move
freely and efficiently if Nature had evolved them.

Its interesting that Nature did evolve an alternative, and more
efficient form of motion than standard legs - that used by Macropods and
similar animals (although they are still, of course, legs). Storing
"elastic energy" is much more efficient than using muscle contraction
all the time. So why isn't that form of motion much more common around
the world? There are a few examples, such as jerboas, but you'd expect a
lot more. Maybe if there is sufficient food, efficiency doesn't matter
so much. So even when that particular evolutionary niche has appeared,
it doesn't mean it's going to be universal. And then, of course, there
are the tree kangaroos!...

Also have a look at the bacterial flaggelum, it isn't a wheel that supports
weight for transport but it does rotate and it is powered by biochemistry.

Indeed, but it's limited to that size of organism. It could not scale
up. I guess it bears a greater similarity to a propeller than a wheel,
anyway.

--

Jeff