On the Other Hand: Left Hand, Right Brain, Mental Disorder, and History by Howard I. Kushner (review)

How to explain handedness, and why do most people prefer their right? The question goes back at least as far as Ancient Greece, when Plato linked handedness to culture, and Aristotle called it natural and inherited. Howard Kushner, author of On the Other Hand, and himself left-handed—among the 10 to 12 percent—calls his interest “as psychiatrists used to say, . . . overdetermined, a combination of personal experience overlaid with clinical observations” (p. 11). It began with the lack of left-handed desks in school, which he’s sure contributed to his inability to master cursive writing.

In twelve chapters and just 154 pages, Kushner tells how laterality researchers address key questions about handedness: how to measure it, whether only humans show it, its proposed cultural, genetic, and evolutionary origins, and whether left-handedness is associated with such characteristics and conditions as criminality, accident-proneness, and physical and mental disorders ranging from stuttering and reading disability to autism and schizophrenia, along with a dramatically shorter lifespan—but also whether left-handers excel in certain cognitive domains, including art and mathematics, and in sports like fencing and boxing.

Anyone seeking an introduction to the enormous, often abstruse literature on handedness, current and past, can learn much from this book. Here are examples from some of the chapters:

“By the Numbers” examines measurement issues, provides a questionnaire for self-assessment, and shows how in decades past and still today in certain parts of the world, practices against left-hand use, especially for writing and utensil use, reduced left-handers’ numbers well below the current figure, at least based on these measures. Their lifespans, however, won’t be reduced: such claims are “overwhelmingly rejected” (p. 36) by laterality researchers.

“Genes and Kangaroos” notes that certain gene variants may be linked to “hand skill” and that other species show limb preference (kangaroos and chimpanzees, for example), although not to the same degree as humans. It also corrects certain pop-psychology ideas about handedness and lateralization of function, among them that the hemispheres have “completely different tasks” (p. 10) and that left-handers are the only ones “in their right minds.”

“Disability, Ability, and the Left Hand” reports a “lack of robust connections” between left-handedness and learning disorders (p. 147) and, similarly, for autism and schizophrenia.

“Criminals or Victims” describes the historical roots of the “tension” between characterizations of left-handers as abnormal and disabled and the idea that they’re “talented victims of discrimination” (p. 15).

“Changing Hands, Tying Tongues” scrutinizes historical and current evidence linking left-handedness and stuttering and asks whether King George VI’s struggles with stuttering (dramatized in the film The King’s Speech) came from having been, like many left-handed children in the early 1900s, forced to write with the right hand.

“Genetic Models and Selective Advantage” goes deeper into genetic models and describes the “fighting hypothesis” designed to explain not only why left-handers have always been a minority but why they exist at all. It supposes that in potentially deadly encounters between left- and right-handers, left-handers, being a minority, were likelier to prevail from having more opportunities to face right-handers than right-handers had against them, and that the same advantage can explain their success in close-interactive contests like fencing and boxing.

On so large a canvas, lapses are understandable. For example, laterality researcher M. Philip Bryden’s first name was Mark, not “Michael” (p. 102); Behavioral Neurology isn’t the title of Norman Geschwind’s “1965 landmark study” (p. 92); it’s the name of the discipline he helped create; there’s no evidence that Julius Caesar was “left-handed” (p. 50); and while it’s correct that for the “vast majority of left-handers, like right-handers,” the left hemisphere leads for speech and language based on evidence of speech loss and impaired...