Oolon Colluphid

By now most of you know my passion for stupid ‘design’ in nature. It occurred to me while reading Fortey’s wonderful <a href="http://www.amazon.com/exec/obidos/ASIN/0375706216/internetinfidelsA/" target="_blank">Trilobite!</a> (only the second science book I’ve ever laughed out loud at) that perhaps some of the silliest pieces of design are those staring us in the face.

Animals with solid supporting skeletons basically come in two sorts, those with endoskeletons and those with exoskeletons. The most obvious exoskeleton owners are arthropods – insects, crustaceans, spiders and scorpions, trilobites, etc -- things that would crunch rather than squish if trodden on. We vertebrates are the most obvious things with endoskeletons; they are inside out compared to us... or we are outside in compared to them.

Now the point. As we grow, with a skeleton inside us we can simply add bone too, so all the materials in the ‘old’ skeleton are reused in the ‘new’ one. Animals with their skeleton on the outside, however, are encased in it, so as they grow, they have to shed their outgrown suit of armour and grow a new one. (This process is called ecdysis.) This is obviously very wasteful of the materials and energy they used to make the old exoskeleton, and leaves them vulnerable while shedding it and till the new coat hardens. This is neither, to use the current buzzwords in UK local government, very sustainable nor Best Value. In other words, it’s crap... but arthropods are stuck with this method by the accident of their history that put their skeleton on the outside.

Note that, as with the backward mammalian retina and blindspot, it’s not that the systems aren’t phenomenally good, efficient, complex etc. It is that they are fundamentally flawed in the first place, that arthropods have evolved excellent ways around a stupid design feature.

But, says the creationist, the Good Lord wanted them to be protected by a hard coating. How can you make a suit of armour grow, eh? Well, I’d do it by making the exoskeleton out of tough plates, and slide new material where needed up between the plates, in the manner of mid-Atlantic ridges adding new ocean floor. Muscle attachments wouldn’t be a problem, since the point of doing this is to accommodate a growing critter. But I’m no engineer, so that’s just an idea. God’s the alleged engineer; and he just scored D minus: must try harder.

Any thoughts / criticisms?

Cheers, Oolon

[ February 13, 2002: Message edited by: Oolon Colluphid ]</p>

Late_Cretaceous

God is a comedian, not an engineer.

Peez

In fairness to any god(s) that may have been involved, a constantly-growing exoskeleton would be a tricky thing to design. The problem is that a "growth line" which produces new skeletal tissue will be a weakness in the structure. Ecdysis is, perhaps, an inevitable price of having an exoskeleton. Having an exoskeleton is, like so many other traits, an advantage in some ways and a disadvantage in others.

Peez

Kevin Dorner

Though I am not sure of which, I am pretty confident that some insects eat their molted exoskeleton (as snakes do their skin) so ecdysis becomes less wasteful. However, not many do this AFAIK.

bluefugue

Also, just to play Devil's Advocate here, Oolon -- the arthropods are a spectacularly successful group of animals. So how much better, really, did the design have to be?

These "bad design" arguments are fun, but of course they can never falsify an Intelligent Designer. The ID'er(s) could be lazy, sadistic, bored, fond of variety for variety's sake, artistically inclined, or any number of other things.

manhattan

See, but Ghod did this as part of His divine plan! Under the current system, it was easier for pre bronze-age people to eat crustaceans.

Oh, wait. Shellfish = no no until well into the iron age. Lemme think about this...

Coragyps

Yeah, Manhattan, you better think about it some more - shellfish weren't just unclean in Moses's day - they were an abomination!

Oolon Colluphid

So Peez, Iesus, Kevin... do we think this one is usable? Not as good as the laryngeal nerve, maybe, but I still think it's an innately arse-backwards design that's had it's disadvantages turned to advantage. Ancestrally, neither was 'inside out', once committed to one way or another, the lineages were stuch with it. And the exo version looks like more hassle, a less elegant design, less of what an expert designer would do, if starting from a clean slate.

To Peex specifically: how do tortoises manage? I know they're not totally encased, but mostly. If I were designing such creatures, I'd give them an endoskeleton and then toughen the outside, like pangolins, armadillos etc. Or is that reinventing the wheel, and they are the odd design...?

Then again, eyes are vulnerable parts whichever way round. Trilobites had this angle covered by making them out of stone: calcite crystals. No other known animal had these. If it was such a good idea, why not? (And if not, why did trilobites have them?)

Or maybe I'm just reluctant to let a pet idea go... Marks out of ten? It all looks like evolution rather than design, but how to turn this to our advantage...?

Oolon

[ February 14, 2002: Message edited by: Oolon Colluphid ]</p>

OrderedChaos

One thing that you are forgetting Oolon is that animals with an exoskeletion are not the only things which shed their outer layers. Reptiles must also shed their skin when they grow. Heck, even humans are constinantly flaking off dead skin cells. I think that haveing to shed your outer layers is pretty much unavoidable.

I don't really think that shedding your outer coverings is that big of a disadvantage anyways. If you kept the same layer of skin your whole life, you would have a very ragged hide near the end of your days. The exoskeletions of insects are not indestructable, like everything the wear out and need to be replaced. Shedding the outer layer also gives the animal a fresh new epidermis.

[ February 14, 2002: Message edited by: OrderedChaos ]</p>

Oolon Colluphid

Yeah, I suppose so. I thought about snakes, and skin cells... it just doesn't seem as drastic as kicking off your entire skeleton though.

Oolon the miserable