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Ligaments and Evolution - cellophane
the story of an invisible girl
renniekins
renniekins
Ligaments and Evolution
The interesting thing about ligaments is that they aren't regenerative. Tendons, muscles, bones, these all will heal themselves when damaged. If you break a bone for example, it will knit itself back together. Ideally you should have it set so that it mends correctly, but the important thing is that the bone will heal itself.

Ligaments on the other hand, do not do this. If you tear a ligament it stays torn. I was thinking about this last night (because I'm an insomniac), and I found myself wondering why this is the case.

Not from a biological perspective: I'm sure there is some cellular reason that doesn't really interest me. But from an evolutionary perspective. Why would a tissue evolve that does not heal itself when damaged? Wouldn't that be counter-productive?

You would think that an organism which heals itself would outlast those which don't. It would live longer and reproduce more, so its characteristics would dominate the species. That's the whole theory of evolution; that's how it works.

The fact that ligaments do not mend themselves must mean that there is some quality they have that is more important than regenerating. In fact it seems to me that this characteristic must go hand-in-hand with not regenerating. Otherwise some form of self-healing should have evolved. There must be something about the ligament's non-regenerative tissue that made it more likely to last. Something that made the species more likely to survive longer. Interesting, isn't it?

Anyway, these are just a computer scientist's muddled thoughts on biology and evolution. Now I'd better get back to Java, where I belong.
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Comments
From: stilldocked Date: January 5th, 2004 09:24 am (UTC) (Link)
it could be the elasticity of the ligament...if they were to regenerate, they would come back stronger, and therefore less flexible...
jkling From: jkling Date: January 5th, 2004 09:25 am (UTC) (Link)
Well, as I understand it, ligaments actually do heal. For example if you sprain your medial collateral ligament (MCL), it will heal on its own.

the problem is specifically with the ACL. I think it sort of floats around in the knee cavity, surrounded by fluid, and so isn't held in place by surrounding tissue. When it tears, the two ends float around randomly. Because they're not held in place by surrounding tissue, they can't find each other and be knit back together.

The ACL surgery works by stitching in a scaffold ligament, typically taken from the patient's patellar tendon. That tissue actually dies, but it holds in place, allowing the body to come in and stitch a new ACL to replace it.
rustymarble From: rustymarble Date: January 5th, 2004 09:29 am (UTC) (Link)
I was going to say what stilldocked said, but what jkling said sounds much much better.

Remember evolution is the mechanism that kept the appendix even though it's not truly necessary in most humans. It's not perfect, but we like it. ;-)
thenisaid From: thenisaid Date: January 5th, 2004 09:31 am (UTC) (Link)
I'm thinking that if it had too much of a tendency to link to itself and regrow, it might link to itself and regrow in the wrong place, locking the joint. And an unstable joint is probably better than an inflexible joint, probably frozen in the most inconvenient possible position. Just a wild guess, but doesn't it sound plausible?
radiantsoul From: radiantsoul Date: January 5th, 2004 11:25 am (UTC) (Link)
~I thought I would be clever, but others have already been so.

Evolution ain't clever.
stillriver From: stillriver Date: January 5th, 2004 02:43 pm (UTC) (Link)
We can blame the modern medicine for messing up the evolution. However, when we are sick, we tend to prefer to get fixed without realizing how selfish it this desire in term of global evolution.

I hope you will be able to have your knee fixed without too many hassles. There were some major improvements in the reconstructive surgery over the last few years and it should make the healing much faster.
renniekins From: renniekins Date: January 6th, 2004 08:53 am (UTC) (Link)
Heehee...I never thought of medicine as being selfish in terms of evolution! So true though. All that human rights and equality and stuff has really thrown off "survival of the fittest" too, come to think of it.

Thanks, I appreciate it.
stillriver From: stillriver Date: January 6th, 2004 09:55 am (UTC) (Link)
You are welcome! Hope everything goes well.

At least we had evolved to some semi-functional state till the medicine and the civilization stopped that.

Someone beleives that our knee joints question the evolution theory all together: http://www.trueorigin.org/knee.asp .
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