Given that I've written a novel about a nocturnal hominid, I was particularly interested in this recent report suggesting that early mammals were nocturnal. Apparently, birds, fish and amphibians all have two versions of a gene that makes cells in the eye receptive to light, but mammals only have one. Noone knows yet exactly what difference this makes, but it does suggest our experience of light may be less rich than that of other vertebrates, and is consistent with the theory that early mammals were nocturnal.