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Why are some people left-handed?

  • Published2 Jan 2014
  • Reviewed2 Jan 2014
  • Author Lesley Rogers
  • Source BrainFacts/SfN

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.

Braccini S, Caine NG. Hand preference predicts reactions to novel foods and predators in marmosets (Callithrix geoffroyi). Journal of Comparative Psychology. 123: 18-25 (2009).

Cameron R, Rogers LJ. Hand preference of the common mamroset: Problem solving and responses to a novel setting. Journal of Comparative Psychology. 113: 149-157 (1999).

Gordon DJ, Rogers LJ.  Differences in social and vocal behavior between left- and right-handed common marmosets (Callithrix jacchus). Journal of Comparative Psychology. 124:402-11 (2010).

Hardyck C, Petrinovich LF. Left-handedness. Psychological Bulletin. 84: 385–404 (1977).

Hopkins WD, Bennett AJ. Handedness and approach-avoidance behaviour in chimpanzees (Pan troglodytes). Journal of Experimental Psychology. 20: 413-418 (1994).

Schiff BB, Lamon M. Inducing emotion by unilateral contraction of hand muscles. Cortex. 30: 247-254 (1994).

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