How Humans' Color Vision First Evolved from a Bi-Chromatic View

How did color vision first develop? Humans see a range of colors that they use to help navigate their everyday lives. Now, scientists have finished a detailed and complete picture of the evolution of human color vision, which involved millions of years of genetic mutations in visual pigments.

In order to better understand the adaptive evolution of vision in humans, the scientists studied ancestral molecules. They first estimated and synthesized ancestral proteins and pigments of a species, and then conducted experiments on them.

The scientists found that five classes of opsin genes encode visual pigments for dim-light and color vision. Bits of the opsin genes change and vision adapts as the environment of a species changes.

"We have no traced all of the evolutionary pathways, going back 90 million years, that led to human color vision," said Shozo Yokoyama, the lead author of the new study, in a news release. "We've clarified these molecular pathways at the chemical level, the genetic level and the functional level."

About 90 million year ago, our ancestors were nocturnal and had UV-sensitive and red-sensitive color. This gave them a bi-chromatic view of the world. Then, about 30 million years ago, our ancestors evolved four classes of opsin genes. This gave them the ability to see the full-color spectrum of visible light, except for UV.

"Gorillas and chimpanzees have human color vision," said Yokoyama. "Or perhaps we should say that humans have gorilla and chimpanzee vision."

In the past, the researchers identified three specific amino acid changes that led to humans developing a green-sensitive pigment. It's these mutations, including others, that are ultimately responsible for human color vision.

"We have no more ambiguities, down to the level of the expression of amino acids, for the mechanisms involved in this evolutionary pathway," said Yokoyama.

The findings are published in the journal PLOS Genetics.

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