Facts about color vision

From an article by Ed Yong (remember, rods ~ night vision, cones ~ color daytime vision):

In 1913, American zoologists Horatio H. Newman and J. Thomas Patterson wrote, “The eyes [of the nine-banded armadillo] are rudimentary and practically useless. If disturbed an armadillo will charge off in a straight line and is as apt to run into a tree trunk as to avoid it…”

A wide range of animals, including many birds, fish, reptiles, and amphibians, have eyes with four types of cones, allowing them to discriminate between a huge range of colours. Mammals, however, evolved from a nocturnal ancestor that had already lost two of its cones, and many have stuck with this impoverished set-up. Dogs, for example, still only have two cones: one tuned to violet-ish colours and another tuned to greenish-blue. (Contrary to popular belief, a dog’s world isn’t black-and-white; they see colours, albeit a limited palette.)

Humans and other primates partly reversed the ancient loss by reinventing a third red-sensitive cone, which may have helped us to discern unripe green fruits from ripe red/orange ones. Ocean-going mammals, meanwhile, took the loss of cones even further and disposed of their blue/violet-sensitive ones. And the great whales have lost all their cones entirely. They only have rods. The ocean is blue, but a blue whale would never know…there are even people who have rod-only vision—they do well in all but brilliant sunlight, and have sharp enough vision to read in normal light. (Then again, Emerling says that this condition is sometimes called “day blindness”, and that “it’s frequently painful for these individuals to keep their eyes open during the day.”)

There are tons of other great little facts about the vision of different animals in the articles.

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