Why are some people left-handed?

Although left-handed humans are in the minority, the fact that they exist suggests there are certain advantages to variations in handedness across a population.

Studies in my lab and others examining behaviors associated with hand preferences in marmosets and chimpanzees have found that lefties are less likely than righties to explore new objects, foods, and environments. Right-hand preference in marmosets is also associated with being more responsive to social situations (e.g. a greater willingness to accept food in a group setting). Such findings suggest that, under circumstances in which new foods might be dangerous, left-handed individuals could be at an advantage. On the other hand, right-handed individuals may be better able to explore new environments and accept new food that is safe to eat. A population would benefit from having both types of individuals.

Whether left- and right-handed people display such behavioral differences has yet to be determined. However, some fascinating studies show that when people are asked to repeatedly contract muscles of their left hand before telling a story, they tell a story with more negative content than those who tell a story after contracting muscles in their right hand. These findings suggest that hand preference in people may influence some aspects of behavior. 

Other studies have shown that people with weaker hand preference are more prone to depression, dyslexia, and schizophrenia. In animals too, it is not just the direction of hand preference but its strength that is associated with particular patterns of behavior. More research is needed to clarify these relationships.

About the Author

Lesley Rogers

Lesley Rogers is emeritus professor of neuroscience and animal behavior at the University of New England. She has been highly honored for her key discoveries in brain lateralization in the animal kingdom, among other work.