A recent study by IFL Science has shown a connection between the dominant hand and brain function. The study shows that left handed people tend to be smarter!
"Left-handers exhibit, on average, a more developed right brain hemisphere, which is specialised for processes such as spatial reasoning and the ability to rotate mental representations of objects.”
They found that left-handed people’s nerve cells that connect the two brain hemispheres, tend to be larger than those in right-handed people, helping increase brain function.
With the world being largely right handed, many people believe that this is also part of the reason why left handed people tend to be smarter - as they are forced to change some of their habits and use different parts of their brain to deal with right handed activities.
They also found that left handed people were greater at problem solving and maths.