wheels

[The_Ryan]

In Why has no animal species ever evolved wheels?
(hopes this works, this the first time I’ve trieds a link on the new board)
Cecil says:

But this may not be an insurmountable obstacle. A flesh-and-blood wheel might use the umbilical hookup found on some merry-go-rounds. Tape one end of a piece of ribbon to a tabletop and the other to the bottom of a compact disc. Turn the CD over so that the ribbon drapes over the side. Now move the CD so that it “orbits” the ribbon clockwise, at the same time rotating the disc clockwise, two rotations per orbit. (Not the easiest thing to explain without diagrams, but think of it as an IQ test.) The wheel turns, but the ribbon doesn’t twist. Would it be easy for a living wheel to evolve something along these lines? Maybe not, but who’s to say it’s impossible?

I think I see what he’s talking about, but isn’t this a revolution rather than a rotation?

(edited to correct link coding: TheRyan, you need to surround the URL with ", something that’s changed with vBulletin. we also have a preview feature now!)
(this post has been edited by Arnold Winkelried)

[pach]

If Cecil is looking for examples of wheels in more complex organisms look no further than Humans. Sperm move in the same way as described for e-coli. There is definitely a wheel in there.

[BigAl]

There are three other problems with animals having wheels - starting, stopping, and steering. If an animal could evolve wheels which rolled, and were therefore disconnected to their bodies except through some type of umbilical cord, what would make the wheels move? They couldn’t just roll everywhere or they would eventually be stuck at the bottom of the hill. There would have to be some type of muscle which would make the wheel turn. I don’t see how that would work. Then they would also need some way to stop, a brake of some sort. Otherwise they would run into things or go over cliffs and natural selection would eliminate them before any advatntage the wheel might have is established. And finally, how would they steer? Some arrangement (another muscle of some sort) would be required. It might be possible to design something that would work but I don’t see how in the world (at least this world) how something could evolve.

[Kyberneticist]

The wheel is the essential part. All the other pieces could be added later.
Like those little scooters people are using nowdays.
There are two wheels. Propulsion/braking is done by feet, but you still move faster.

Or, for a pure wheel setup, you could have a projection that rubs against the wheel to stop it as a friction brake.
You could have another that pushes against the making it move by friction. Or, say, a series of projections in the wheel for it to hook into to push it, then retract for it to rotate, or hook into to stop it.

Use your imagination!

[Arnold_Winkelried]

The column (including Slug Signorino’s illustration) can also be found on pages 209-211 of Cecil Adams’ book “Triumph of the Straight Dope”.
In Cecil’s article, he mentions how humans have difficuties in creating “robot limbs that faithfully duplicate animal motion”. So perhaps the biological wheel is a step down the evolutionary ladder? Perhaps a biological wheel was tried in the past and discarded because arms and legs were better?

pach, are you sure about spermatozoa moving by rotating their “tails” in a circular fashion?

Here’s what Encyclopædia Britannica has to say on the subject:

The tail gives the sperm cell movement. It whips and undulates so that the cell can travel to the egg.

This sounds more to me like what Cecil Adams described as “twisting back and forth like a washing machine agitator”.

[pach]

Yes, I’m sure. The “tail” of the sperm or the Coli that Cecil mentioned is actually corkscrew shaped and rigid. The corkscrew revolves around like a propeller to move the sperm/coli.

When you look at it from above, and in one dimension (eg. Through a microscope) it looks like the “tail” is wiggling back and forth, like a fish swims.

If you pin down the back of the “tail” (no easy task) you will see the body spin around.

[andros]

Now, I’m not trying to say you’re wrong, pach, but that’s a little different that I understand it. Please feel free to show mw otherwise, it’s been a while since my bioanatomy classes.

The structure of cilia and flagella is nicely described at The Biology Project at Arizona State University. The have some pictures of spermatozoa in cross section as well.

In short, however,

Both flagella and cilia have a 9 + 2 arrangement of microtubules. This arrangement refers to the 9 fused pairs of microtubules on the outside of a cylinder, and the 2 unfused microtubules in the center. Dynein “arms” attached to the microtubules serve as the molecular motors. Defective dynein arms cause male infertility and also lead to respiratory tract and sinus problems.

Not a wheel by any means, but I think I get what you mean. There’s a really cool disjunction (the inner microtubules are essentially unattached to the walls) that’s similar to the spinning axle problem. It doesn’t spin regularly, though, and not always in a circle, so it is said to whip about fairly unpredictably. I do recall seeing some sperm flagella under scope that moved pretty regularly, but not many, and not for long (even the regular ones only went in nice circles for brief periods of time). This what you’re thinking of?

[zut]

I recall seeing an eposide of Nova (I think) years ago where they filmed a sperm cell whose tail had been glued down. When it tried moving, the “body” clearly spun around, rather than wriggling back-and-forth. I’m not 'zactly sure wher to find evidence of this, but I do remember seeing it.

[andros]

zut, you’re welcome to be with pach. I’m not denying that the sperm flagella spin, sometimes in nice round circles (more often not). All I’m saying is that while the sperm flagellum spins, it’s not a wheel. A nitpick, perhaps, but true nonetheless.

Now a disjuncted flagellum, as I said, certainly helps solve the axle issue, but we have yet to attach a round thing to the axle to permit, well, rolling. Which, as I understand it, is kinda the wheel sort of thing we’re talking about.