Comparison of the anatomy of various plants and animals provide indirect evidence of their evolution from common ancestors. The front flipper of a seal, a cat’s paw, a horse’s front leg, a bat’s wing and your own hand all look different and perform different functions. However, they all consist of the same number of bones, muscles, nerves and blood vessels arranged in a similar basic pattern. The basic pentadactyl limb (a limb with 5 digits) can be traced back to the fins of a certain fish from which the first amphibians are thought to have evolved. These fundamentally similar structures are called homologous structures.
Basically, there are a lot of animals (mostly mammals) that have a very similar arm structure. They have 1 upper bone, 2 lower bones and lots of bones that make up “fingers”. All of this is pointing towards the idea of them having a common ancestor.
Next in our line up: the reclusive Comparative Embryology.
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