Whales cannot see blue
I was doing some reading on colour perception recently, and came across a fascinating paper¹ by a team of scientists who had examined the eyes of whales and seals.
Most mammals have two kinds of cones in their retinas. These are sensitive to green and blue light respectively, and give the animal a limited kind of colour vision.
We humans, along with our close cousins among the great apes, have evolved a third kind of cone, sensitive to yellow and red light, and this allows us to distinguish a wider range of colours. It's how we tell green from red, for example.
Whales and seals have no blue-sensitive cones. They have only green-sensitive cones, and they therefore see in monochrome.
This loss of colour vision occurred separately and independently in these two groups of marine mammals. It's not a trait inherited from a common ancestor. As such, it appears to be an example of convergent evolution: the same trait arising independently in two unrelated groups of animals which occupy similar habitats. There must be an evolutionary benefit, but the authors of the paper are at a loss to explain what it might be.
¹ Peichl, L., et al, "For whales and seals the ocean is not blue: a visual pigment loss in marine mammals", European Journal of Neuroscience, Vol. 13, pp. 1520-1528, 2001
Most mammals have two kinds of cones in their retinas. These are sensitive to green and blue light respectively, and give the animal a limited kind of colour vision.
We humans, along with our close cousins among the great apes, have evolved a third kind of cone, sensitive to yellow and red light, and this allows us to distinguish a wider range of colours. It's how we tell green from red, for example.
Whales and seals have no blue-sensitive cones. They have only green-sensitive cones, and they therefore see in monochrome.
This loss of colour vision occurred separately and independently in these two groups of marine mammals. It's not a trait inherited from a common ancestor. As such, it appears to be an example of convergent evolution: the same trait arising independently in two unrelated groups of animals which occupy similar habitats. There must be an evolutionary benefit, but the authors of the paper are at a loss to explain what it might be.
¹ Peichl, L., et al, "For whales and seals the ocean is not blue: a visual pigment loss in marine mammals", European Journal of Neuroscience, Vol. 13, pp. 1520-1528, 2001