When Did Nature Burst into Vivid Color?

Summary

In the animal kingdom, there is incredible variation in visual perception. What an animal sees depends on the structure of its retina and its neural visual processing system. Most insects can see ultraviolet, blue and green light, but there is wide variety among arthropods; mantis shrimp eyes have up to 12 different channels of color, revealing the ultraviolet spectrum and polarized light. The ancestor of living vertebrates could likely detect red, purple, blue and green — an ability that was maintained in lizards, birds, lampreys and lungfish, among other vertebrate groups, Wiens said. But some components of color vision have been lost over evolutionary time. Hagfish can’t detect red. Sharks can’t see blue. Human eyes have three photoreceptor cones that allow us to make out blues, greens and reds, but dogs and rabbits have only two cones, which reduces the number of shades they can distinguish. Wiens and Emberts’ data supports the hypothesis that color evolved for some as-yet-unknown reason before any of these flashy signals. “It was color vision first, then fruit, then flowers, then warning signals and then sexual signals,” Wiens said. Coming and Going The researchers’ effort to reconstruct deep time is admittedly imperfect. Colors don’t readily fossilize, and when they do, scientists can’t infer the color’s function unless the animal has living descendants. And for all the data they involve, evolutionary trees are inherently speculative. Some traits can evolve multiple times in different lineages. For example, juniper berries and blueberries are both blue, but their ancestors may have developed that coloration separately. Other traits can come and go, like the lizards’ blue belly patches. If we know that signals can disappear and reappear over millions of years, it’s hard to be certain that a common ancestor actually possessed that shared trait. A vivid color, whether it’s a pure pigment or a reflective structure, takes action to organize. “This evolutionary labi...