In the scientific literature, convergence is far from surprising. In Futuyma's Evolutionary Biology , the second of seven "principles of evolutionary change" is "homoplasy [convergence] is common in evolution": When a similar character (or character state) in two organisms has not been derived from a corresponding character (or state) in their most recent common ancestor, it is said to be homoplasious. An example of a homoplasious character is the superficially similar eye of vertebrates and of cephalopods (squids, octopods). Both have a lens and retina, but their many profound differences indicate that they evolved independently: for example, the axons of the retinal cells arise from the cell bases in cephalopods, but from the cell apices in vertebrates. … Three more or less arbitrarily distinguished kinds of homoplasy are recognized. In convergent evolution (convergence), independently evolved features are superficially similar, but arise by different developmental pathways. The eyes of vertebrates and cephalopods are an example.
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