Vadebichos: Wheels are for cars, but not so much for animals. Si eres un animal... las ruedas no son una gran idea

viernes, 17 de septiembre de 2021

Wheels are for cars, but not so much for animals. Si eres un animal... las ruedas no son una gran idea

Because it is not a good idea for animals moving on wheels. That’s a consequence of how multicelullar organisms are built in, and how do motion wheels operate.

Yes, yes, we have a few animals that exhibit incomplete cogs as an ornament, such as the intimidating wheel[1] bug (Arilus cristatus):

And more impresionant than this, we have at least one genus of animals, the Issus -a common kind of planthoppers- that uses functional (incomplete) gears to power the jump of its legs; this mechamism was described in the juvenile of Issus coleaptratus, adults lack these cogs in their hind legs. I fell messmerised by this gif the first time I saw this images:

Here are the cogs[2], each one sitted on one hind leg.

In the image bellow[3] we can see how they are positioned in the legs, and understand how they work; when the young Issus prepares to jump the two sets of teeths lock together, transferring mechanical power and synchronization to its legs. If you want a more detailed explanation, I recommend to watch this video

By the way, here is the geared planthopper itself

Wow, amazing, yes, however those are not locomotion wheels. Right.

I told that having wheels for locomotion is not a great idea for multicellular organisms. Let’s roll!, there are a lot of good reasons:

First off, a locomotion wheel needs to rotate freely, 360º. And to do it, it has not to be physically attached to any biological structure that avoids this movement. But… living organisms need to give nutrients and physicall support to all the living cells in their bodies, otherwise these structure would die and rotten.

Think about your joints, they got that name for a good reason, you have muscles, tendons, veins and arteries connected to them, it would be impossible for your bone rotate 360º freely once and again.

Wheels don’t propel themselves, they need to be moved. And once again, an animal would need to have muscles attached to those wheels, with the paradox that they need muscles to rotate, but can’t rotate because they have muscles.

This is because, contrary to man made machinary, biological organisms haven’t found the way of functioning with electromagnet motors or hydraullic piston and have to rely on the old Biological reactions that give cells their energy.

It could be argued that some animals could develope rounded free structures, and we have an example of an apparently freely rotating “rod”, despite it is used for digestion, not for propulsion: the cristaline style made of glycoproteins of some gastropods and bivalves, Wikipedia has a good diagram:[4]

So we could think… hey, why not developing a keratin or glycoprotein propulsion wheel… we have hair and nails (don’t we?) and they are conveniently “not alive”, so why not a keratin wheel… and here is another disadvantage of wheels…

Wheels need a lot of maintinance because the friction against the soil wear them out, constantly. And remember, our guess was an animal growing a functional free wheel, so this animal couldn’t regrow/repair the wheel on the go, it would need to get rid of it and grow a new one. If moulting supposes a waste of energy and danger for birds, can you guess how dangerous would be to replace wheels and being unable to move while on?

And there are many more reasons (wheels need roads, need brakes, it is difficult to control the speed, the direction, etc)… that’s why when organisms turn themselves into living wheels it is when they are scaping from something or just they are totally disposable and spreading their seeds[5] (talking about plants).

All in all, the reason is in multicellularity, it doesn’t combine well with propulsion on wheels. It is physiologically impossible to maintain a wheel-shaped limb, which means that the rotating parts are not directly connected to another body part in order to be able to rotate. They cannot be connected neither with veins nor with supporting tissues. And making disposable wheels would be an extraordinary waste of energy for the animal (or the plant).

Interestingly enough at a mollecular level… we have the flagelums of bacterias, but there are some other very interesting examples, such as a protein Ferris wheel structure that cell organelles use to regulate the pH of their environment, a yeast proton pump called vacuolar ATPase (V-ATPase). And it looks spectacular[6]: