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See the Evolution of Human Color Vision

Dec 22, 2014 08:13 AM EST

Researchers have long known that many mutations in visual pigments, spread out over millions of years, were required for humans to be able to see the colorful world that we can today. Now, in a new study, one team of scientists has finally painted the complete picture to see exactly how human color vision evolved.

Around 90 million years ago, our primitive mammal ancestors had a dim, shadowy vision of the world. And now after two decades of painstaking research, a team at Emory University has revealed the evolutionary pathways it took for modern humans to eventually see all the colors of the rainbow.

"We've clarified these molecular pathways at the chemical level, the genetic level and the functional level," lead author and biologist Shozo Yokoyama explained in a statement.

Though this breakthrough was the result of a rather length process involving estimating and synthesizing ancestral proteins and pigments of a species. Then a series of advanced analytical techniques revealed five classes of opsin genes that encode visual pigments for dim-light and color vision. According to the study, bits and pieces of the opsin genes change and vision changes and adapts as a species' environment changes.

Through this mechanism, by 30 million years ago, out primitive ancestors had evolved four classes of opsin genes, taking them from nocturnal, UV-sensitive and red-sensitive color, to the full-color spectrum of visible light (except for UV).

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

Additionally, the researchers also set out to identify which amino acid changes were required to bring about the genetic changes to make human color vision possible. Out of a staggering 5,040 possible pathways, they found seven.

"Each of them individually has no effect. It is only when several of the changes combine in a particular order that the evolutionary pathway can be completed," Yokoyama explained.

This complete evolutionary pathway, developed over millions of years, is explained in more detail in the journal PLOS Genetics.

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