No. 36: Nov-Dec 1984
Depending upon which estimate you believe, 6 to 16% of us are left-handed. On the surface, left-handers seem little different from right-handers. So why the highly skewed population? Why not 50% of each? Dr. Peter Irwin, at Sanddoz, Ltd., of Basle, Switzerland, has what is certain to be a controversial answer. He was led to his conclusion by a series of experiments with psychoactive drugs, performed in collaboration with Professor Max Fink, SUNY, Stony Brook. Left-handers, the study demonstrated, are much more sensitive to drugs that act upon the central nervous system. Irwin believes that this finding is consistent with the known association of left-handedness with epilepsy and learning disorders.
"But perhaps the most exciting aspect of Irwin's hypothesis is that it makes evolutionary sense. 'A greater resistance of right-handers to centrally active substances, when Man was a forager and before he learned to identify non-toxic edibles, would have favoured righthanded survival. This might account for the skew in the present handedness distribution that is unique to humans.'"
And why should left-handers be more sensitive to psychoactive substances? Irwin thinks they must absorb or metabolize them differently, or perhaps there is a difference in the blood-brain barrier that affects the transport of substances into the brain.
(Grist, Liz; "Why Most People Are Right-Handed," New Scientist, 22, August 16, 1984.)