Who is Colour Blind?

 

Seeing the World Differently: The Truth About Colour Blindness

Have you ever looked at a bright red apple nestled in green leaves and marvelled at how clear the colours are? For some people, that apple and the leaves look almost exactly the same. This is called red-green colour blindness, and it is the most common type of colour vision deficiency in the world.

While it affects people everywhere, it is noticeably more common in people of Western European descent. Let's explore exactly why this happens and how it works.

How We See Colour

To understand colour blindness, we first need to look at how a healthy eye sees colour. Inside the back of your eye, there is a layer called the retina. This layer is covered in millions of tiny light catchers. Some are shaped like rods, and some are shaped like cones.

The rods help us see in the dark, but the cones are the stars of the show when it comes to colour.


You have three types of cones:

• Red cones: Catch red light.
  
  
• Green cones: Catch green light.
  
  
• Blue cones: Catch blue light.
  
  

When these cones work together perfectly, your brain can mix those three colours to create every single shade you see in a rainbow. But if the red or green cones are faulty, or missing altogether, the brain gets confused messages. Red and green start to look like murky shades of brown or grey.

It is All in The Genes

Colour blindness is not an illness you can catch. It is something you are born with, hidden inside your DNA.

To understand why it happens mostly to men, we have to look at chromosomes, which are the instruction manuals for our bodies. Men have one X chromosome and one Y chromosome. Women have two X chromosomes.

The instructions for building red and green cones live on the X chromosome.

• For a boy: Because he only has one X chromosome, if that single chromosome carries the faulty instructions for colour vision, he will be colour blind.
  
  
• For a girl: She has two X chromosomes. If one has faulty instructions, the second one usually has healthy instructions and steps in to do the job. A girl will only be colour blind if both of her X chromosomes carry the faulty gene.
  
  

Because of this simple biological math, about 1 in 12 men of Northern European descent are red-green colour blind, compared to only 1 in 200 women.

The Western Connection

So, why are the numbers so much higher in Western populations?

It boils down to human history and something scientists call "genetic drift." Thousands of years ago, early humans lived in small, isolated groups. If one particular group happened to have a few extra people carrying the colour blind gene, and that group later migrated and settled in Western Europe, the gene spread rapidly as their population grew

In some other parts of the world, like parts of Africa and Asia, the rate of colour blindness is significantly lower simply because those ancient settling groups did not have as many people carrying the trait.

Being colour blind does not mean a person is unhealthy. It just means their eyes process the world's canvas a little differently. They might need to organise their clothes by labels rather than colour, or memorise the order of traffic lights, but they go on to live perfectly normal, healthy lives.

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