Colours in the dark

After the sun has set and darkness falls, our eyes can no longer see in color. The reason for this is that the cells responsible for color vision, the cones, need a certain amount of light to function.

In our eyes, and in the eyes of other vertebrates, there are two kinds of photoreceptive cells that make vision possible: rods, that helps us distinguish patterns and contours but not colors, and cones, that react to different wavelengths of light, i.e. different colors. Rods are generally more sensitive to light and can still function after the sun has set. But in most animals (as far as we know) as well as ourselves, the cones stop working when the light level drops.We can still see the world, but in black and white. “In the darkness, all cats are grey”. But through the eyes of a seal the world is always grey, since they lack cones all together.

Humans have three kinds of cones; red, green and blue. The red cone is unique to primates amongst mammals and enables us to see the color red. This is a useful trait when you want to find ripe fruits and vegetables. Animals lacking the red cone, horses for instance, can´t tell a red apple from a green one. At least not in the way humans do.

We may lose the ability to see colors after dark, but at Lund University, Almut Kelber and her group of researchers, focusing on animal vision, have discovered that there are nocturnal species of Gecko lizards, living in Northern Africa, that can still see color after the sun has disappeared. During evolution, diurnal Geckos have lost their rods. Vision in these lizards rests solely on cones, even in some nocturnal Geckos. In order to see, they have evolved specialized cones that work in the dark.

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