I hope you will share the following article re animals and color by Higgs, the Science Cat with your children or grandchildren.-BBL
Two weeks before my last birthday, I discovered the perfect present. (We call it my birthday, but it’s really the anniversary of my human finding me.) One of my social networking friends is a neurobiologist named Mark Changizi, and in February he posted a notice that he’d invented glasses that could help correct color blindness. I was so excited some of my fur stood up.
Cats and dogs are commonly considered color blind. People have done experiments showing that we can distinguish yellow and blue, but we can’t tell yellow from red from green–which is somewhat the same situation faced by humans with the most common form of color blindness, affecting about 8% of human males.
The glasses go for $300, which is a bit pricey, but my human companion is very fond of me, so I didn’t think it was out of the question. We both decided to do a little research on color vision first, during which I learned that I am not really color blind.
We cats see some colors, and you humans may see more, but other animals see colors you can’t imagine. It’s easy to think that colors are intrinsic aspects of the outside world, but in fact there are infinitely many ways that living things can sample reality.
The world isn’t really colored–it’s made up of surfaces that absorb and reflect light at different wavelengths. Cat eyes have retinas with two kinds of cells called cones, and these cones sense two different wavelengths. Our brains interpret them as blue and yellow. The cones do some tricks so that we also see a whole range of shades in between blue and yellow.
Humans get a third cone that senses another wavelength, which allows you to see shades from green to red–an entire dimension of color I can’t see.
A number of reptiles, amphibians, fish, birds, and insects have four cones, so they must see colors that you humans can’t conceive of. An animal called a mantis shrimp has 12 cones, which must make its universe colorful beyond our wildest imaginations–though they may be using their color sensing cells in ways we mammals can’t understand.
My human has learned a lot about color vision from her friend Dr. Jay Neitz, who is a professor at the University of Washington. He explained that cone cells use molecules called pigments to distinguish different wavelengths of light, and the pigments we mammals use originated in bacteria, long before eyes ever evolved.
Bacteria that use the sun for photosynthesis can benefit from sensing when the sun is at a safe, low angle, and when it’s high noon. They need some sun, but too much can kill them. If they live in the water they can move deeper when the sun might fry them, and return to the surface when they sense the gentler, more orange light of late afternoon.
So color sensing is very ancient. And a three-cone system seems to have appeared early in the evolution of animals, since many fish, reptiles, amphibians, and birds use at least three cones. But alas, it appears that somewhere along the line we mammals lost our third cone. The vast majority of mammals see the way I do.
My eyes have the same color-sensing cells as dogs, and scientists can do experiments on dogs to understand what colors they can and can’t see. Dr. Neitz designed a set-up in which he shows a dog three shapes, two of the same color and one different one. The dogs get a treat if they press their noses on the shape with the different color.
That test showed dogs can tell blue from yellow from white from grey, and they will diligently press the right shape because dogs will do almost anything for a treat. So when dogs failed to pick yellow from green or red, the scientists concluded that it was not from lack of effort. (Some cats will participate in the same experiment, but we’re more difficult subjects because in general we’re a lot picker about treats.)
Which leads back to the question of why humans have three cones when cats, dogs, mice, rabbits, horses, cows, and most other mammals do fine with two? Apparently a mutation arose in an ancient primate–a common ancestor to humans and other apes as well as some monkeys. Why did they get so lucky and not cats? One very interesting theory comes from Dr. Changizi–the scientist who invented my birthday-wish glasses.