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Question: Do animals see in color or in black and white?
A few years ago, the prevalent scientific belief was that human's best friend, our faithful dog, could only see in black and white. I remember thinking that certainly did not seem fair, especially when I looked over at my best friend at the time who was looking back at me, wagging his tail and smiling from ear to ear. What possible reason could there be for an evolutionary development that led to him not being able to see in color?
Much has changed since then in our understanding of the natural world. Today the common response according to most scientists is that many, if not most, animals see in color to some extent. It all comes down to what scientists term 'cones' and 'rods.' For simplicity, scientists offer the following general rule: most diurnal (daytime) animals see in color, while most nocturnal (night) animals do not seem to be able to see in color to the same degree. In humans, rods and cones in the eye's retina detect light and color, respectively. Rods allow us to see shapes in dim light and make our way down the hall in the middle of the night. Cones, which detect color, require more light to activate. Have you ever noticed that when you enter a darkened room, everything appears in shades of gray? Flip on a light, and the retina's cones activate, relaying color information to the brain.
Humans have three sets of cones for detecting different colors: cones that detect red wavelengths, cones that detect blue, and cones that detect green, though there is some overlap among the three. Animals such as our household friends, cats and dogs, have two sets of cones, making them color-blind to specific colors. They do, however, have many more rods than humans, giving them greater night vision and a keener ability to detect motion.
The retina of nocturnal animals is almost entirely composed of rods. The other type of vision cells, cones, is absent or almost absent, leaving nocturnal animals with virtually no color vision. The photosensitive pigment inside the rods is particularly sensitive to low levels of light. During the day, in a daylight-adapted eye, the pigment breaks down so rapidly; it is ineffective for visual perception. At nighttime, in the rod-rich eyes of dark-adapted animals, the pigment is created faster than it breaks down. Therefore, the threshold of light needed to stimulate the eye is reduced. It is just a minute fraction of the light needed to activate a cone cell for vision during the day. Examples of animals with nocturnal sight include owls, cats and dogs.
I began to think back again to the many 'best friends' I have had throughout my lifetime. It still did not make sense as to why they were destined to spend their lives in primarily a black, white and shades of grey kind of world. There are too many games of catch and Frisbee to play! Yet, then it began to make sense as I thought about the ancestor of all dogs from Chihuahuas to Alaskan Malamutes, the wolf. A wolf's eyesight is just about as good as that of a human being. Wolves have excellent peripheral vision and their eyes are optimized to detect motion. In addition, they have a very high ratio of rods (grayscale receptors) to cones (color receptors) in the retina; in fact, about 95% rods. This abundance of rods aids the wolf in the ability to see at night. A wolf's night vision is far superior to that of a human being. So rather than being a limitation, my dog's eyesight actually tells of his/her connection to an exciting and awe-inspiring past.
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