Roughly one tenth of the world's population is left-handed. And, according to this video from TED, archaeological evidence shows that it's been that way for over 500,000 years.
But why are some people left-handed and others aren't?
Despite what people may think, being left-handed or right-handed is not a choice. In fact, handedness can be predicted before birth based on the foetus' position in the womb.
The chances of being right or left-handed are determined by your parents - in surprisingly consistent ratios.
For example, if a father was left-handed but the mother was right-handed, a child would have a 17% chance of being born left-handed. If it was the other way around, and the mother was left-handed, the child would have a 22% chance of being born a leftie.
Meanwhile having two right-handed parents means the child has a 10% chance of being born left-handed, and having two left-handed parents means the child has a 25% chance of being born left-handed.
According to the video, a recent mathematical model suggests that the actual ratio of left and right-handers reflects a balance between competitive and co-operative pressures on human evolution.
For example, in a purely competitive world 50% of the population would be left-handed. But human evolution has been shaped by co-operation as well as competition. And co-operative pressure pushes handedness distribution in the opposite direction.
The benefits of being left-handed are clearest in activities involving an opponent, like combat or competitive sports (they have the advantage of surprise). However when it comes to using tools, left-handed people don't have as much luck and are more likely to have an accident.
Intrigued? Watch the video to understand more about the wonderful world of left-handedness.
