On 12/19/10, Henry Baker <hbaker1@pipeline.com> wrote:
I keep asking my friends in the evo-devo (evolutionary development) community why 5-fingered hands and 5-toed feet in humans are so resistant to variation -- particularly relative to the variation found in many other traits. From time to time, there are a minute fraction of people who are born with extra fingers and/or toes, but this seems far less common than many other not-so-rare traits which are incredibly debilitating.
There's little light to be cast by screw theory here. Exactly the same analysis applies as to bicycle spokes --- or rather cartwheel spokes, since fingers act as struts (in compression) rather than ties (in tension). Picking up a slippery sphere requires (at least) 7 fingers. WFL