Eyeing the evolutionary past

March 09, 2008

[That some human photoreceptors use c-opsin, and others r-opsin,] tells us something about the last common ancestor of animals--that it might possibly have had multiple kinds of receptors and eyes, and that what we observe in the diversity of extant eyes is not that it is easy to evolve an eye, but that it is easy to lose one or the other kind of eye in a lineage.

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