why do we have five fingers?

After I used my five fingers to put my foot squarely in my mouth on the APOGEE Collaboration mailing list (yes folks, apparently you should be careful with that Reply All button), I was treated late in the day to a couple of excellent talks about NYU efforts that border on astrobiology; not astrobiology per se but close: Paul Chaikin (NYU Physics) talked about his work with Pine and Seamans to make artificial structures out of DNA or small particles painted with DNA or the like that can self-assemble and then self-replicate. Bud Mishra (NYU Math and Biology) talked about simulations of the interactions that lead to multi-cellularity, with the thought that multi-cellularity might be inexpensive and generic in the path from first life forms to complex ones.

One of Mishra's most gripping (ha ha) points was about the number of fingers we have: Is five a random accident or is it something you would expect to see on other worlds? He pointed to a nice math result of his that shows that for frictionless fingers to hold any arbitrary solid object under load, you need between 7 and 12 fingers. Given that fingers come at a cost, and that there is friction, five might be very close to optimal for a wide range of utility functions! That's an idea I will be thinking about for a while. I also got him to say a bit about higher dimensions: He said my problem wasn't crazy because an articulated object is like a solid object in higher dimensions!