• Question: How developed is the human eye in terms of identifying colour? Are there any other animals who may have a more developed eyesight and what structures in their eyes cause this?

    Asked by delaram123 to Dilwar, Lou, Rachel, Simon, Susan on 16 Nov 2013.
    • Photo: Susan Skelton

      Susan Skelton answered on 16 Nov 2013:

      Hi delaram,
      The human eye is an amazing thing! Usually we’re pretty good at detecting different colours – otherwise our world would look like an old black and white film. But this only works when there is enough light. When it gets dark at night, there isn’t enough light for us to be able to see colours, so everything looks grey.

      We see colour by detecting different colours of light. The human eye has four types of special cells which detect different types of light: there are “rod” cells, which are sensitive only to black, white and shades of grey, and then there are three different types of “cone” cells, which each detect a different colour of light, either red, green or blue.

      In bright sunlight, the cone cells work well and tell us if something is red, purple, yellow, etc. But when it is darker, the cone cells struggle to work and we rely on our rod cells to tell us the shapes of objects.

      Some other animals are better at seeing colour than we are, as they have more different types of cone cells.

      The animal with the most cone cells is the mantis shrimp, which has 12 different types of cone cells – 4 times as many as us!

    • Photo: Simon Langley-Evans

      Simon Langley-Evans answered on 16 Nov 2013:

      The eye has two sorts of cells which have receptors that detect light and then send nerve impulses to the brain. Rod cells enable us to see in black and white and function most efficiently in dim light. Cone cells contain photoreceptors which contain a pigment called rhodopsin, and this enables us to see in colour.

      Humans have good colour vision which many animals do not.It was really useful to our species as we evolved as we relied more on vision to find our food than smell (the opposite to a dog for example, which has lousy colour vision but an amazing nose). that other mammals don’t have. Early humans will have relied on eating fruits and berries and being able to see in colour would have helped us to find them (bright colours can be seen from a distance) and to tell the difference between ripe and unripe, safe and poisonous. Seeing colour also helps us see through camouflage so might have helped us avoid predators. Being able to see colour might have been an advantage in competing with other species that did not have colour vision.

      Creatures with more cone cells will see better in colour than we do. Susan has given you the example of the mantis shrimp. There is variation in humans too. Some people are colour blind because they lack the cone cells which see a particular type of colour.

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