Consider the visual system Vision is a dominant sense in hum

Consider the visual system. Vision is a dominant sense in humans. And, many animals rely heavily on the ability to process movement and visual detail for their very survival. But here is something you may not have considered... Have you ever noticed that animals like deer, raccoons, and dogs have \"eyshine\" at night? If you have ever taken a picture of your dog, you probably noticed that they don\'t have the typical \"red eye\". Rather, their eyes glow! How might this be explained? If you were looking at this visual feature from an evolutionary perspective, what adaptive advantage might it have? Are there possible disadvantages? Why don\'t humans have one?

Solution

The “eye shine” which appears in animals like deer, raccoons and dogs in night is attributed by the presence of a layer of tissue named “ Tapetum Lucidum” lying immediately behind the retina in such vertebrates .

The advantage of such evolutionary perspective is that the “Tapetum Lucidum” along with increased number of rods than cones in the retina, a larger lens, larger optical aperture and larger eyeball contribute to the better night vision of these animals compared to human. It reflex the visible light back through the retina there by increasing the light available to the photoreceptors enabling superior night vision even in dimmer light.

The only disadvantage is it reduces the sharpness of the focus of the image but the anatomy of the rods in nocturnal mammals is inverted soon after birth into inverted rods. This along with thick layer of retina enables the processing of even low light without change in focus.

The eyeshine is the visible effect of the tapetum lucidum. When light shines into the eye of the animal having “tapetum lucidum”, the pupil appears to glow. The colour of the glow depends on the colour of the tapatum lucidum, for example in tigers its greenish; in dogs it is whitish with a blue periphery.

Humans lack the tapetum lucidum so they don’t have the eye shine or the eye glow.