KEY POINTS:
For some reason about 12 per cent of New Zealanders are left-handed - and an Auckland University study aims to find out why.
Researchers will examine whether the "handedness" is shaped by genetics, or other causes, including how a baby is lying in the womb.
The researchers also aim to prove whether brain asymmetry - which side of a person's brain drives different functions, like speech - is genetically inherited.
Most people's speech is driven from the left side of their brain, but for one in 10 it is driven from the right side.
The general view had been those trends were governed by genetics, study head and Auckland University psychology professor Michael Corballis told the Herald yesterday.
But if that were true, identical twins should always be of the same handedness, he said. That was not the case, as 22 per cent of identical twins had opposite handedness, despite being genetically identical.
One theory suggested handedness was a symptom of lying in the womb, Prof Corballis said, where one hand tended to be freer and have more movement. In twins those free hands could be the opposite in each baby.
Another theory suggested handedness was a learned trait, as society was set up for right-handed people.
However, Prof Corballis said it was more likely there was a gene that caused right-handedness, and in that gene's absence the handedness of a baby became random.
He said there was little evidence to suggest brain asymmetry had an impact on people's personality.
The researchers hope to attract 50 identical and 50 non-identical sets of twins, aged between 15 and 50 years. The twins will be scanned in an MRI scanner showing both the structure and functioning of their brain.
The three-year, $750,000 study has been funded through the Government's Marsden Fund for "blue skies" research, and was being completed in the name of scientific curiosity, Prof Corballis said.
