Why has no animal species ever evolved wheels?

You can’t think of how an animal would have wheels?
It doesn’t make me think of replacing animals’ legs, but rather a dog pushing a wheelbarrow.

Or, if you’re wanting an animal with wheels for legs:
Picture that you’re holding a bar of soap in your hand, and you squeeze the soap, it flies forward, and proceeds to hit you in the eye.

Using that thought, picture this:
A wheel on a rotating axis, with small triangles on the flat sides, arranged in such a way that the triangles form a circle of triangles around the flat sides. when a bar/bone/whatever pushes against the triangles on either sides of the wheel, then it pushes the wheel around.

There’s millions of examples of muscles that could push the bone/bar back & forward against the triangles on the side of the wheel, eg the heart.

Perhaps even triangles closer to the centre of the wheel for higher gears, and triangles closer to the outer edge of the wheel for lower gears.
Or even a huge ridge from the outer edge to the center, for an entire spectrum of gears.

Or For a diagram (thanks to mspaint) go to:
http://homepages.ihug.co.nz/~davoman/animal_with_wheels.gif

Well, have a most excellent day, and party on…

Blub!!

DavoMan

And the column being referenced is Why has no animal species ever evolved wheels?

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And how is this complex mechanism supposed to evolve?

Not to mention the fact that bone is not dead.

Actually, a number of animals have wheels of a sort.

The best example is the paramecium which has a freely rotating motor on a axel that turns the flagella around and around generating its propulsion.

Even human cells have motor of a similar nature embedded in their cell walls for various purposes (not propulsion).

And of course, inchworms and other animals are known to roll up into a disk or ball and roll them selves along. But this is not a wheel rotating on an axel.

However, I am not aware of any multi-cellular motor or axel.

I think the basic problem is that a wheel requires a bearing and seals for said bearing. Single cells can indeed create bearings and seals at a molecular level where chemical forces are suffient. But Macroscopic sized bearings exceed the capacity of simple chemical forces to manage. Or so I speculate.

Cecil’s final point struck me as especially relevant: Wheels aren’t useful in nature. Right now NASA is spending huge sums of $$ trying to figure out how to replicate the most primitve walking movementsfor Mars exploration. A biological wheel would have very limited use on a pre-paved earth.

There are other adaptations that are equally suited only for specialized niches. In the case of the wheel, however, coupling this with how unlikely they are to gradually evolve in the first place (as Cecil and everyone else here already described), and it’s no wonder wheels haven’t evolved beyond the microscopic level. If it were to happen at all, the earliest adaptations would most likely need the most ideal surface (pavement) for the first few million years.

Or, if you prefer Creation-based theory, God didn’t make biological wheels because he didn’t want to.

[nitpick] Actually, bigkahuna, the cilia and flagella of eukaryotic cells (i.e. Paramecia and humans) don’t rotate, but bend back and forth due to contractions that cycle around the circumference. Several proteins pull against each other and shorten first the 12 o’clock position, then the 1 o’clock position, etc. causing a whipping motion. Only in prokaryotic (bacterial) flagella are there truly wheel-like structures, where a bearing-like connection between the flagellum and the ‘motor’ allows the flagellum to spin around like a propeller. [/nitpick]

-b

While it is true that at microscopic scales rotating structures and bearings are seen - flagellates being the obvious example - the problem involved with multi-cellular organisms is not just one of powering the wheel assembly but of providing it with oxygen and nutrients without impeding its free rotation. This limitation does not apply to microscopic organisms as their energy requirements can be met directly from the surrounding medium in the form of dissolved glucose or ATP etc.

A multicellular structure needs some form of circulatory system to provide all its cells with oxygen and nutrients. Such a system would be hard to evolve in a manner compatible with a freely rotating wheel and axle.

One possible way round this (for instance if designing a new life form) would be to have the wheel as a separate symbiotic organism with its own circulatory system - a plant-like creature with rigid wooden frame, using photosynthesis and absorbing moisture from the atmosphere would work - it wouldn’t have to grow much once it reached mature size so energy demands would be low.

The wheel creature would be linked to the main organism via bearings derived from the creatures ancestral limbs. They may reproduce separately and find their wheels on attaining maturity, or change their wheels throughout life as hermit crabs change their shells.

I don’t think this could easily evolve naturally though, as more efficient methods of locomotion would probably be favoured by natural selection.

Anyway, that’s my small stab at speculation on this topic…

In addition to the fact that wheels are less useful when travelling over rough surfaces, I can’t see how a wheeled creature could effectively climb trees, or anything else. A flexible limb, with claws for gripping, is the proven champ.

Besides, I don’t expect wheels would lend themselves to reproductive success. Too much chance of a flat, if you know what I mean.