Why 10 fingers?

[Catso]

Anybody any ideas as to why nature/selection settled upon 5 as the optimum number of fingers/toes per limb? (Please don't sink to saying 'I only have 4'). This design is quite widespread, I believe, even if some fingers have now atrophied away in some species.

So why 5? Wouldn't 4 have worked just as well (and been an even number)? Even 3 could have worked OK.

[4getmenot]

No ones ever gonna know. Not bein nasty but what a strange question :-) why do we only have two legs unlike spiders that have 8. why no wings so we can fly. Who knows???

[WoWo]

Often in evolution things have come about not because they alone have caused the mutation to be come dominant. For example an Elephants trunk, for much of the evolution of the elephant the trunk would have been a useless stump, however some other mutation combined with the stump would have cause the animal to be "fitter" than one without the trunk mutation, better eyesite or hearing for example.

While it's true 3 or 4 could have been as good there is no reason why 5 was a problem.

[Octavius]

It is possible that a strain of human evolved with 3 or 4 or 15 fingers but died out long ago as the modern-fingered humans were better equipped to hold, throw things (spears etc) and the variants evolved in different ways or became extinct.

Some people have more than the usual number of fingers or toes. This is normally caused by a genetic condition called Polydactyly. Others may have more than the typical number of metacarpal bones, a condition often caused by genetic disorders like Catel Manzke syndrome. Alternatively, some may have large hands, and others small hands.

Its just one of those thing(er)s

[Clanad]

Or, maybe not. Dr. Mark Changizi, Sloan-Swartz Center for Theoretical Neurobiology, Caltech, proposes a hypothesis, called the "max-MST hypothesis". The hypothesis predicts a particular relationship between the body to limb ratio of an organism and its number of limbs. As a specific example, consider the five fingers on your hand. Your palm is the "body," and your digits are the "limbs." The only crucial difference between digits and limbs is that there is only a need for digits along roughly the outside half of the palm, whereas limbs are typically needed for animals all the way around. If you look at your hand, you will notice that your finger length is roughly the same as your palm diameter. Changizi has developed an equation (not included here) which (greatly simplified) predicts a finger to palm ratio of 4.71, which is about 5. We have five fingers, then, because given that the limb ratio k = 2/3, five fingers is the economical solution. With this in mind, we can predict that, for any animal anywhere (Earthly or otherwise), if it has been selected to have hands capable of closing, then it will have approximately five digits... (Source: Cognitive Science and Theoretical Neurobiology)

[woodchopper]

I prefer to believe that the Good Lord wanted us to have ten :o)

[Octavius]

...approximately 5 digits...??

http://en.wikipedia.org/wiki/Pentadactyly