Evolutionary convergence occurs when unrelated organisms evolve similar adaptations to similar environmental or selective pressures, arriving there by very different routes. Here is a famous example. As you look out onto the world you do so through what we call a camera-eye, with a lens suspended between two fluid-filled chambers. Perhaps surprisingly, the octopus also has a remarkably similar camera-eye (as do squid and cuttlefish), yet we know that the octopus belongs to an invertebrate group called the cephalopod molluscs, evolutionarily very distant from the vertebrates (or speaking more widely the chordates), to which of course we belong. Our knowledge of animal relationships tells us that neither the common ancestor of molluscs nor chordates could possibly have possessed a camera-eye, so quite clearly they have evolved independently; the same solution has been arrived at by completely different routes.
The Map of Life documents many more examples of convergence for you to explore, and in fact in the case of the camera-eye alone there is much more to be said. The camera-eye has actually evolved at least seven times, most extraordinarily in a group of jellyfish known as the box-jellies (or cubozoans). Although these jellyfish have a nervous system, they don’t have a brain, and furthermore they belong to a phylum known as cnidarians, widely agreed to be amongst the most primitive of animals.
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