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Why can I grow new toenails, but not a new leg?

Writing a kids book and need a good resource on this question. Any suggestions...?

Comments

Michael Fisher said…
This is a great 24-slide powerpoint that could be simplified

Rgrds Michael Fisher

http://www.qpowerpoint.com/Why-Cant-We-Grow-New-Arms--PPT.html
September 16, 2011 at 9:24 AM
Michael Fisher said…
Not sure it 'took' first time

http://www.qpowerpoint.com/Why-Cant-We-Grow-New-Arms--PPT.html
September 16, 2011 at 9:29 AM
Paul P. Mealing said…
Salamanders are the best known animals for regenerating limbs, and eyes apparently. I found this after a quick search, which provides a not-too-esoteric explanation.

As for toenails, like hair, they don't stop growing unless they fall out. Same as rodents' teeth, including beavers. If they don't wear them down by chewing timber they'd grow into their lower jaw.

So toenails are a completely different process to regeneration, which requires different types of cells: skin, bone, cartilege, blood vessels; to generate.

Regards, Paul.
September 16, 2011 at 1:04 PM
jeremy said…
As far as I know, this question doesn't have a universally agreed-upon answer, but the closest I think anyone has come is the theory by Randolph Nesse and George Williams, in their book Evolution and Healing. (Annoyingly, the book has a different name in America: "Why We Get Sick".) See the short "Regeneration of Body Parts" section of the "Injury" chapter.

Fundamentally, their answer is that evolution won't maintain capacities whose average benefit is low. However, their argument is quite shrewd, and nuanced.

If you can't obtain the relevant section easily, I can send you a summary of their arguments, if you'd find it helpful. However, getting hold their (wonderful) book would be better, I think.
September 16, 2011 at 7:48 PM
Eric Sotnak said…
Some information here:
http://www.sciencemag.org/content/309/5731/84.full
September 18, 2011 at 4:53 PM
RS Gold said…
I recently adore this kind of tute! Thanks for expressing countless nice tips here just about all! I really like your talent with regard to materials. Lord Appreciate it you! RS Gold
January 14, 2012 at 6:51 AM
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