From: Henry Baker <hbaker1@pipeline.com> To: Fred lunnon <fred.lunnon@gmail.com> Cc: math-fun <math-fun@mailman.xmission.com> Sent: Sun, December 19, 2010 2:50:30 PM Subject: Re: [math-fun] Five-fingered hands 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. Given the effort required during development to enforce this 5-digit constraint, there must be extremely powerful evolutionary factors involved. Darwin's Theory of Sexual Selection provides one possibility: that having exactly 5 digits/hand/foot is extremely sexy, but this is a cop-out. For some reason, humans tend to think that cartoon figures with only 4 digits (thumb + 3 fingers) are extremely cute. There must be some extremely important tasks for which are impossible with only 4 digits/hand, as well as other extremely important tasks which are impossible with more than 5 digits/hand. Even if the evolutionarily important tasks involved counting, what on earth is so important that 5 or 10 is just the right number? Are the digits used for counting the months during gestation? Perhaps the husband has to be back in 10 months from his latest war? If he comes back too soon or too late, terrible things happen? Perhaps certain important foods only achieve ripeness after 10 days, but become rotten in 11 days? ________________________________ It appears that at one time in our distant evolutionary past, we counted in hex. See the essay by Stephen J. Gould, "Eight Little Piggies". -- Gene