Who sees the best rainbow?

By Steve Roark | The Winchester Sun

Humans are appar­ent­ly hard-wired to love see­ing rain­bows, as proven by all the Facebook post­ings that pop up when­ev­er one appears in our area.  But have you ever won­dered if, say your dog sit­ting beside you, sees the same rain­bow you do? Or how about oth­er ani­mals? Let us delve into col­or vision by var­i­ous res­i­dents of our planet.

Let’s start with us.  A rain­bow to us has 6 col­ors: red, orange, yel­low, green, blue, vio­let (ROYGBIV mem­o­riza­tion trick). Some con­tend that on real­ly clear days folks with good vision can see 7 col­ors, with anoth­er shade of vio­let thrown in (ROYGBIVV). Now back to your dog sit­ting beside you. His rain­bow would start out as blue, then green, a sliv­er of yel­low, and… that’s it. A dog’s rain­bow is only half as thick as yours. So he’s sit­ting there smil­ing and pant­i­ng like he’s enjoy­ing it, but in real­i­ty, he’s think­ing “what’s the big deal?”

The dif­fer­ence between us and dogs is that they only have two pho­tore­cep­tors in their eyes, which if you remem­ber from biol­o­gy, are called cones. They only have blue and green sen­si­tive cones, while we have those plus a red one. You wouldn’t think one more recep­tor would make much dif­fer­ence, but three is way, way bet­ter than two because it allows a bunch of oth­er col­ors to become vis­i­ble.  Mix red with blue and you get pur­ple, red with yel­low gives you orange, and so on.  The addi­tion­al cone allows us to see about 100 dif­fer­ent shades of col­or, 96 more than your dog can see. He should be envi­ous, but his sit­ting there lick­ing him­self indi­cates that he could care less.

What about the spar­row flit­ting around in the tree behind you as you enjoy your rain­bow? It varies among bird species, but spar­rows can see into the ultra­vi­o­let col­or band and have more sen­si­tive red cones than we do. Their rain­bow would start out extreme­ly red, very red, red, orange, green, blue, vio­let, and ultra­vi­o­let. A much broad­er rain­bow than ours, so per­haps we should be envi­ous of sparrows.

But hold on, what about that swal­low­tail but­ter­fly feed­ing on the flower at your feet? Turns out they have five kinds of pho­tore­cep­tors, so there would be an amaz­ing rain­bow with mul­ti­ple shades of all the col­ors we see and bunch­es that we don’t.  So wow, hats off to butterflies.

This leads to the ques­tion of what ani­mal sees the best rain­bow ever? The present cham­pi­on is the man­tis shrimp, an ocean dweller that lives on coral reefs with shal­low, clear water, and so could, were it so inclined, see a rain­bow. These guys have 16 kinds of col­or recep­tors, and their rain­bow would be unbe­liev­able. They would start out like super-duper ultra­vi­o­let, 6 more shades of ultra­vi­o­let, then vio­let, vio­let-blue, blue, blue-green, green-green, green-blue, bluey-blue, blue, and on it goes until they hit red and blow­ing our rain­bow out of the water. 

Of course, our human advan­tage is that we have the cog­ni­tive abil­i­ty to see and appre­ci­ate the beau­ty of rain­bows, even if ours is more diminu­tive than what is seen by oth­er ani­mals. Still, wouldn’t see­ing a 24-lay­er rain­bow be awesome? 

Information for this arti­cle came from a radio pro­gram called “Rippin the Rainbow” pro­duced by Radiolab.  Look up the pod­cast online and lis­ten to it, as it’s very entertaining.