The retinas in the eyes of whales and seals do not contain cells that react to blue light-they lack what are known as blue cones. They only have the green cones, and are therefore color-blind. Biologists suspect that the ancestors of today's whales and seals lost their blue cones when they changed their habitat, moving back into the sea. Initially, they would have remained in coastal regions where impurities made the water a greenish color. Under those circumstances, the loss of the blue cones would have been an advantage, since it simplified the processing of information in their brains, thereby freeing up capacity for other functions.
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