Why do cats chase laser pointers?

Chris Smith put this question to zoologist Chris Basu.

Chris B - She’s spot on. Cats aren’t great at seeing red colours; they’re actually red/green colorblind. So at the back of our eye (the retina), we have light sensitive pigments that enable us to see colour and cats don’t really have the pigments that enable them to see red, so they can’t distinguish red and green lights.

Chris S - They can still see the light but they cannot tell the difference between a red light and a green light. It’s just a patch of light to them?

Chris B - Exactly. It doesn’t really matter what colour the laser pointer is but what they lack in colour perception they really make up for it in terms of their ability to see things like dim light.

So, at the back of our eye we’ve got different kinds of cells that help us see light. We’ve got the cones which are full of these pigments that help us see colour and then we’ve got rod cells. Rod cells are really good in dim light and they’re really good for picking up darty kinds of movements, and cat’s retinas are jam packed full of rod cells.

If you look at a laser pointer and imagine it from the viewpoint of a cat, cats are really good at seeing this dim light so a laser pointer really shouts and stands out at them. In terms of their evolution, they’re primed to chase and see quick, darty movements so it’s really the perfect stimulus for them.

Chris S - Have they evolved not to be able to see the rich range of colours that we have purely because they are really nocturnal animals? They hunt at night when there’s low light and, under those conditions, you can’t actually see colours anyway.

Chris B - It’s a question that lots of people have asked before. If you imagine the mammalian ancestor - a small potentially nocturnal anima, that’s one idea that mammals as a group have lost the ability to a wide spectrum of colour. And it’s only as you go further down the evolutionary line when you get to animals like primates, although their ancestors may have lost some of these colour-sensitive pigments, primates have regenerated that ability to a certain extent. So primates, like us, see colour and that’s because we’ve regained that ability through time.

Chris S - So a cat wouldn’t be able to tell the difference between a ripe and an unripe strawberry for example?

Chris B - No. Cats would be really terrible at picking fruit. Yes, really, really rubbish at that job.