my question has always been why (I think most vertebrates) stop at two? It seems that an extra eye here and there could be really helpful. Maybe it's because all verterbrates evolved from an ancestor that had two eyes, and once the template is in place, it was simply too deep a local maximum to evolve out of? Similar to the 5-digit hand design that all vertebrates share.
TFA is about the fact that originally the vertebrates had at least 3 eyes, 2 lateral eyes and 1 median eye (pointing upwards towards the sky, in the middle of the head). Most vertebrates, with the exception of a few species, like tuatara, have lost the middle eye. The subject of the parent article is that it was expected that if the third eye was lost, the retinas of the 2 lateral eyes that have been preserved are de…
Re: The rise of eyes began with just one
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