In his great work On the Origin of Species Charles Darwin wrote:
'What could be more curious than that the hand of man formed for grasping, that of a mole, for digging, the leg of a horse, the paddle of a porpoise and the wing of a bat, should all be constructed on the same pattern and should include similar bones and in the same relative positions?'
The structure of your own arm includes a bone between the shoulder and the elbow called the humerus. Below the elbow are 2 other bones, the radius and the ulna, followed by a set of wrist bones and then the 5 fingers or digits. This is an example of a pentadactyl limb, which is common to humans, other mammals, birds, dinosaurs, and other reptiles and amphibians.
The pentadactyl limb is evidence of humans' common ancestry with amphibians, reptiles and other mammals. Or, if you are a creationist then I guess it means that once the great creator in the sky had hit on a good design he/she/it stuck to it.
This is the flipper of a grey seal, complete with 5 digits!