We Didn’t Evolve Color Vision to See Color

Summary

Color and color vision are separate evolutionary traits. An organism can produce conspicuous colors, but those colors function as signals only if other organisms can perceive them. A 2024 study reviewed evolutionary trees, previous research, and fossil evidence to investigate which trait evolved first and what colorful traits may have been used for.

How color is produced and perceived

• Pigments absorb some wavelengths of light and reflect others. Flamingos, for example, get their pinkish color from carotenoid pigments in their diet.
• Structural color results from microscopic structures that reflect light in particular ways. It produces the blue color of Blue Morpho butterfly wings and mandrill snouts.
• Some organisms combine pigments and structural color.
• Color perception depends on an animal’s photoreceptors, light-sensitive proteins called opsins, and the brain’s interpretation of their signals. Different species perceive different ranges of light: honeybees, for instance, see ultraviolet light but not red as humans do.

Why conspicuous colors may have evolved

The researchers compared five proposed explanations for conspicuous coloration:

• Fruits became colorful to attract animals that spread seeds.
• Flowers became colorful to attract pollinators.
• Color developed as a warning signal, or aposematism.
• Color evolved to attract mates.
• Color vision evolved before these forms of conspicuous coloration.

Their method combined previous studies into evolutionary, or phylogenetic, trees; used fossil evidence where possible; and compared the estimated timing of different traits.

The approach has limits. Evolutionary reconstructions become more uncertain further back in time, traits can appear or disappear rapidly or evolve independently, and color is rarely preserved in fossils.

Estimated timeline

• Fruit-like seed coverings: Some gymnosperms had bright, fleshy coverings around their seeds roughly 307–299 million years ago. These were not true fruits, which develop in flowering plants.
• Flower colors: Flowering plants began using vivid hues to attract pollinators around 200 million years ago. Insect pollinators existed earlier and visited gymnosperms.
• Colorful fruits: Some early flowering-plant groups with fleshy fruits may date to around 200–250 million years ago. Overall, the study’s evidence suggests that fruits were the oldest colorful feature in its comparison with a clear function.
• Warning coloration: Evidence suggests aposematism may have appeared around 130 million years ago. A Lebanese cockroach fossil preserved in amber shows distinctive warning coloration, and evolutionary studies point to insects, possibly an ancestor of certain butterflies and moths. A 1998 proposal that some Cambrian fossils used iridescence as a warning was described as highly speculative.
• Mating displays: Flashy coloration used to attract mates appears to have developed around 100 million years ago, especially in arthropods and chordates. Fish fossils suggest sexual color differences around 97 million years ago. An older exception is the feathered dinosaur Anchiornis, from about 160 million years ago; its red head feathers may have been used in mating displays. This example illustrates that a trait can arise and later disappear with extinction.
• Color vision: The study suggests color vision may have evolved much earlier, around 550–500 million years ago, likely in an arthropod ancestor. This predates the conspicuous biological colors considered in the study by hundreds of millions of years.

Researchers can investigate color vision in living animals by examining their visual systems, though opsins alone do not prove that an animal sees color. Behavioral tests, such as the grey card method, train an animal to associate a color with food and then test whether it chooses that color over grey cards.

Why color vision might have come first

The early world was not literally colorless: water, sky, rocks, and photosynthetic organisms could all create color contrasts. Color vision may have helped animals distinguish objects or navigate, rather than evolving specifically to see colorful displays.

A 2000 paper proposed that, in shallow water, color vision might have helped ancient marine animals interpret high-contrast, flickering patterns created by sunlight passing through surface ripples. The exact evolutionary sequence remains uncertain.

Researchers and sources featured

• Two evolutionary biologists, unnamed in the subtitles, whose 2024 paper compared the evolution of conspicuous coloration and color vision.
• Two surveys reviewed in that paper on the timing of mating-related coloration; the authors were not named.
• Prior phylogenetic studies used to estimate the evolution of warning coloration; the studies and authors were not named.
• A 1998 study proposing that Cambrian fossils used iridescence as a warning; the author was not named.
• A 2003 review of color vision in modern animals; the author was not named.
• A 2000 paper proposing a visual benefit of color vision in shallow water; the author was not named.
• Fossil evidence discussed includes Anchiornis, a Lebanese cockroach preserved in amber, and fossil pollinators with pollen.