Shutterstock/Martin Mecnarowski
Why didn’t green fur evolve among mammals, when there are birds with green plumage and reptiles with green skin?
Herman D’Hondt
Sydney, Australia
Reptiles and birds have three types of colour-sensing cone cells in their retinas that are each sensitive to a specific colour – usually, there are red, green and blue receptors. They also have a fourth type that works in the ultraviolet range. Mantis shrimp can have up to 16 different types of cones: what they use them for is anybody’s guess.
When mammals first evolved from reptiles, they lost one or two of these receptors. This may have…
