The main problem with wheels is that they have to freely rotate, which means they must either be:
-Alive in their own right, as separate organisms
-Made from dead material
-Alive, but connected to the circulatory system by some kind of coupling that can cope with the rotation without disconnecting or leaking.
The most plausible fictional example I can think of would be something like a mollusc with feet that can rotate a loose shell-like wheel/foot from the inside.
I can come up with yet another mechanism for biological wheels. To illustrate, picture yourself on all fours, holding a wheel axel in each hand. Your wheels, being attached to your circulatory system, can only rotate a limited amount before they get too “twisted up”. Roll forward that amount with the palm side of your hands facing forward. Now, rotate your wrists such that the back of your hand is facing forward, and roll more. Now, your wheels will be untwisting. Rotate your wrists back, and repeat.
And this is an improvement on walking how?
I never said it was an improvement. The two objections to animals having wheels is that first, it would be difficult to arrange the various connections (blood vessels, nerves, etc) such that they wouldn’t get twisted up, and that second, even if you could configure that, that legs are better than wheels over most natural terrain anyway. I was not addressing the second objection, but only the first.
Nice one - is there not some organism that actually does this, or something like it (it seems oddly familiar).
For ingenious examples of wheeled creatures from science fiction, see the works of Piers Anthony (Polarians, from the Cluster series) and David Brin (g’Kek, from his Uplift novels).
Breifly described, Anthony’s Polarians aggregate a horn- or nail-like sphere, which is gripped in a socket and manipulated by many tiny cilia. They balance atop the sphere, and also use olfactory-type organs among the cilia to detect chemicals picked up by the sphere from the ground.
Brin is much less detailed about his g’Kek, though they actually have two wheels and an axle. If I recall correctly, he describes this equipment as grown with an umbilical that then atrophies. Locomotion is performed with strong muscles acting upon the axle. This puts the creature at a distinct mechanical disadvantage at low speeds, but then perhaps there was more that I missed. I found Brightness Reef and its sequels rather boring and skimmed thru much of them. Perhaps a more studious Brin reader can supplement my description.
I’m sure there are other examples of biological wheels from SF, but these are the best two I can recall offhand.
And yet, strangely enough, Paris Hilton is a biped. Go figure…
An important thing to notice about the g’Kek is that, as every other species (except man) in the Uplift universe, they’ve been raised from simple animals to sentient beings by another race. Most likely the proto-g’Kek didn’t have wheels, and it’s described in one of the novels that the g’Kek civilisation was very into roads, ramps and elevators, since they were not good at getting around offroad and couldn’t negotiate stairs.
So the even the ficitonal g’Kek didn’t evolve wheels by natural selection.
That reminds me of the Daleks, the mechanised alien baddies from the cult BBC TV series Doctor Who. The Daleks were articially created mutants who needed a wheeled - and heavily armed! - protective casing to survive.
Anyway many years ago I saw a cartoon where two Daleks were confronted by a staircase, and one says to the other “Well, this certainly buggers our plan to conquer the universe!” I was hoping to find it somewhere on the Internet, but haven’t been able to. I did come across this nice artwork though, which illustrates the Dalek’s problem nicely.
Mmmmmmm . . . air breathing land clam.
Philip Pullman also thought up a wheeled creature, the Mulefa, which appears in The Amber Spyglass (last book in His Dark Materials trilogy).
The Mulefa are described in Random House’s Amber Spyglass glossary as “cattle-like creatures dependant on large round seedpods they use as wheel attachments at the bottoms of their legs” though that’s slightly misleading as they’re not fully dependent on the seedpods.
The Mulefa’s legs have evolved a kind of hook, which they can place into a depression in the seedpod and which is lubricated from the seed oil. They can then roll the seedpods along roads they’ve built to travel at very high speeds. After the seedpods have been rolled on the hard flat surface for a while, they split open and are left to germinate. The Mulefa can still walk, so are also able to navigate less even terrain. I don’t recall whether Pullman explained how the Mulefa power the seedpods though.
CLAMS HAVE FEET!!!
(Fifteen points to the person who can name the source. 
)
Clearly, when serious genetic engineering gets to be common, we’re going to see some REALLY weird pets! 
It sounds like something from B.C., but I don’t recall that specific one being used. In any event, in the real world, a clam has exactly one “foot”.
Ding-ding-ding! And you probably don’t recall 'cause it’s ancient history. (No pun intended. Well, maybe.)
I believe the canonical form is “Clams got feet!”
Remember the article about how lighted signs rotate without breaking the power wire? Well, couldn’t that work with an arterie/vien and an animal wheel?
I think I’m onto something, but can’t find the link, or explain how an electric sign spins.
Help.
No. You don’t even need to bring up a lighted sign, any electric motor or generator illustrates the point. Blood cannot be carried (in sufficient quantity, on a non-microscopic scale) by brushes.
Rotating electrical connections don’t necessarily need to use brushes. In a merry-go-round, for instance, one typically has an umbilicus of wires coming up through the middle and connecting to the rotating part. Perhaps surprisingly, this only requires the wires in the umbilicus to flex, not to twist. A similar system could conceivably be used in a biological wheel.
That cannot work. No matter how long the connection is, it will still twist, and eventually need to be untwisted. There must be, at some point, some kind of slip-ring, brush, or similar arrangement.
