Trinity Redmond, of Green Island School, asks :-

Why do we have five senses?

Phil Heyward, a physiologist at Otago University, responded.

To answer this, let’s think about what our senses allow us to do. Think of yourself as an animal (which all humans are of course), and what your single most important goal as an animal is. It is to stay alive. To stay alive you need to find food and water, and avoid being food for other animals. You need to avoid injury. And you also need to reproduce, creating other animals to carry on your species.

To achieve these goals, animals need information about what is going on around them. The more information they have, the more successful at staying alive they can be. And the more complicated their needs are, the more information they must have. For example, a very simple animal made of just a few cells, living in a pond, can detect chemicals dissolved in the water around it. This allows it to swim towards food. But it is much more likely to stay alive if it can also detect predators. Other animals can be detected by sensing their vibrations and moving shadows. But more information, more senses, are needed to determine whether the other animal is a predator to be avoided, or a potential mate to be approached.

Humans actually have more than 5 senses, giving us information about chemicals in the air or in water, vibrations in the air or on our skin, heat and cold, injury to our bodies, light and colour. We also sense when our bodies are moving, and which way is up. Some animals have more senses than we do. Platypuses and sharks can detect electric currents made by other animals in the water, and migrating birds can detect the earth’s magnetic field. The kind of senses we have is determined by what we need to know to survive.