Color vision: A gene mutates in the primeval forest, and we see red
Dogs with their two cones are dichromatic. They can see in color, but are limited to a range of blue and yellow hues. Eric Rasmussen holds up a color wheel to show the range of colors a dog can see. LD (Little Dog) looks away, heartbroken to learn he can’t enjoy all the colors his human buddies see.
by Eric Rasmussen
Color vision comes from the ability of cone cells to capture energy from light, and transmit this energy as meaningful signals to the brain.
But like a fussy toddler who will only eat mac and cheese, cone cells only respond to certain colors of light. For an animal to perceive different colors requires different types of cone cells, encoded with different genes.
Animals with only one type of cone gene (and therefore, one type of cone cell) are called monochromats, and see in shades of black, white and gray. Monochromats typically live in low-light environments and include marine sea mammals like seals, sea lions, walruses, dolphins and whales. Nocturnal land mammals like bats, rodents, and the mischievous raccoon are monochromatic also.
As light in an animal’s environment increases, so, too, does its tendency to adapt and add more types of cones.
Contrary to popular belief, dogs have two cones, so are dichromatic. They can see in color, but are limited to a range of blue and yellow hues. Humans have a leg up on our canine friends because we have three cone genes. Because of the amazing blending features of color (e.g. red and blue create purple; yellow and red make orange), humans can see about 100 times more colors than dogs.
The mantis shrimp leads the animal kingdom with its 16 different color-receptive cones. How must the world look to that creature?
The mantis shrimp leads the animal kingdom with its 16 different color-receptive cones. How must the world look to that creature?
Even more incredibly, old-world primates like chimpanzees and bonobos share the exact same color genes as humans. These three genes, OPN1SW, OPN1MW, and OPN1LW, shed light on both the world around us and our biological history.
Before 3.5 million years ago, old-world primates only possessed two cone genes. By random chance, a mutation event occurred in the OPN1MW gene, and it duplicated a bit awry. The resultant mutation was sensitive to a slightly different form of light. Trichromatic vision in the primate kingdom was born.
Primates with this mutation had an advantage. They could spot fruit and predators more easily in a dense forest. Individuals possessing this mutation then became more likely to survive long enough to reproduce, so trichromatic vision rapidly expanded through the population. Ultimately, through time, it traveled through various organisms and lineages to finally come to rest inside our own genes.
Yes, you read that right. Today’s humans not only share the same mechanics of sight with all old-world primates, we also enjoy trichromatic color vision because one of those long-ago genes mutated to an ancestor’s advantage. That single gene passed through generation after generation to come to dwell in us.
The next time we visit a zoo, we should all stare in a chimpanzee’s eye and revel in the fact we and he are both seeing each other in the same hues and tones, thanks to the same genetics.
A trichromat like us humans sees the image to the left; Middle depicts what a dichromat like a dog sees. Far right shows the world of a monochromat. What a difference an extra cone gene makes.
Photo 1 Source:
Extended Reading & Photo 2 Source:
https://www.frontiersin.org/files/Articles/262267/fevo-05-00034-HTML/image_m/fevo-05-00034-g005.jpg
Eric Rasmussen, BS, M.Ed., obtained his bachelor of science degree at the University of Colorado at Boulder. He majored in ecology and evolutionary biology, and now serves as a Learning Technology Coach at Erie High School and Erie Middle School in the St. Vrain Valley School District, CO.
Patrice Johnson
Editor in Chief of Stockbridge Community News. Author of national award winning, "The Fall and Rise of Tyler Johnson"