Why do we need to see in color?
The next two images will show you why.
Here you see a black-and-white version of a jungle scene.
If it took you more than a second to spot it, consider yourself dead. See the color-image of the jungle scene below. Did you spot the panther?
Why was the panther so difficult to find earlier? Why is it so easy to spot in color? Color enables us to see a greater number of similarities and differences between objects, which is necessary for survival. Vision evolved mainly to discover objects and to defeat camouflage.
Now you see it, now you don’t
Color Vision in other animals
Most birds are tetrachromats or have four types of cone cells; red, green, blue and ultraviolet. Their spectrum extends to the UVA range of 300-400 nm. Although birds are not the only ones who have UVA vision (fish, amphibians, reptiles, and insects also have the ability), it does provide them with evolutionary advantages.
The standard Venn diagram for color has 7 colors. Red, green, blue, cyan, magenta, yellow and white. The Venn diagram based on four primaries has 15 colors in it. The seven we know of and eight more which are the 4th primary a tetrochromate sees and seven more which are the combination of that primary (Gbeen) with the initial seven.
Why do birds need color vision?
There is a strong correspondence between the habitat and behavior patterns of different species, and their spectral sensitivities.
One possible advantage of ultraviolet vision is in spotting the traces left by prey. The urine and feces of mice are visible in the ultraviolet range, so they stand out against the uniform color of a cultivated field to the eyes of a hunting bird.
Flowers that look plain to us may actually be lavishly decorated with spots or stripes for the benefit of insects, ornamentation that we can’t see because we are blind to ultraviolet. Many flowers guide bees in to land by little runway markings, painted on the flower in ultraviolet pigments, which the human eye can’t see.
The evening primrose (Oenothera) looks yellow to us. But a photograph taken through an ultraviolet filter shows a pattern for the benefit of bees, which we can’t see with normal vision.
In the photograph it appears as red, but that is a ‘false color’: an arbitrary choice by the photographic process. It doesn’t mean that bees would see it as red. Nobody knows how ultraviolet (or yellow or any other color) looks to a bee. A meadow full of flowers is nature’s Times Square, nature’s Piccadilly Circus.
References and Related Material:
- The science of optical illusions
- Color Vision in Birds
- A bees-eye view: How insects see flowers very differently to us
- “The Greatest Show on Earth”, by Richard Dawkins
- Umwelt – TED
David Eagleman – Can we create new senses for humans?