It may have more to do with your spine than your brain.
Left-handedness has puzzled scientists for a long time.
Lefties aren't very common. In fact, just 10 per cent of the world’s population is left-handed.
Being a rarity comes at a price though. Lefties have been treated pretty badly throughout history.
The word "sinister" comes from "left" or "left hand", while the Irish word for left-handed is "ciotóg", which translates to "awkward person".
However, there are some perks - it's been proven that left-handed people are more creative and have better problem-solving skills.
There's been a few theories over the years as to why some people use one hand over the other. Previous research has suggested that left-handedness is due to genetic differences in the right and left hemispheres of the brain.
But the latest theory is that the the spinal cord determines our dominant hand.
According to scientists at Ruhr-Universitat Bochum in Germany, our preference for using our left or right hand begins in the womb.
Researchers discovered that babies show signs of right or left-handedness at just eight weeks. However, the motor cortex (which controls arm and hand movements via signals to the brain) and the spinal cord don't connect until the 15th week of pregnancy.
This means that the brain can't control hand preferences - it must be the spinal cord.
So, what can lefties take from this?
Your dominant hand is determined by genetic differences in your spinal cord before you're even born, and as there's so few left-handed people this means your genes are extra-special.
