Matt Kean

How many senses does a human being have?

At least nine. The five senses we all know about – sight, hearing, taste, smell and touch – were first listed by Aristotle, who, while brilliant, often got things wrong. (For

example, he taught that we thought with our hearts, that bees were created by the rotting carcasses of bulls and that flies had only four legs.) There are four more commonly agreed senses:

1 Thermoception, the sense of heat (or its absence) on our skin.

2 Equilibrioception – our sense of balance – which is determined by the fluid-containing cavities in the inner ear.

3 Nociception – the perception of pain from the skin, joints and body organs. Oddly, this does not include the brain, which has no pain receptors at

all. Headaches, regardless of the way it seems, don’t come from inside the brain.

4 Proprioception – or ‘body awareness’. This is the unconscious knowledge of where our body parts are without being able to see or feel them. For

example, close your eyes and waggle your foot in the air. You still know where it is in relation to the rest of you.

Every self-respecting neurologist has their own opinion about whether there are more than these nine. Some argue that there are up to twenty-one. What about hunger? Or thirst? The sense of depth, or the sense of meaning, or language? Or the endlessly intriguing subject of synaesthesia, where

senses collide and combine so that music can be perceived in colour? And what about the sense of electricity, or even impending danger, when your hair stands on end? There are also senses which some animals have but we don’t. Sharks have keenelectroception which allows them to sense electric fields,

magnetoception detects magnetic fields and is used in the navigation systems of birds and insects, echolocation and the ‘lateral line’ are used by fish to sense pressure, and infrared vision is used by owls and deer to hunt or feed at night.