Life span studies have shown that the population percentage of left-handers diminishes steadily, so that they are drastically underrepresented in the oldest age groups. Data are reviewed that indicate that this population trend is due to the reduced longevity of left-handers. Some of the elevated risk for sinistrals is apparently due to environmental factors that elevate their accident susceptibility. Further evidence suggests that left-handedness may be a marker for birth stress related neuropathy, developmental delays and irregularities, and deficiencies in the immune system due to the intrauterine hormonal environment. Some statistical and physiological factors that may cause left-handedness to be selectively associated with earlier mortality are also presented.

Left-handedness: a marker for decreased survival fitness.

Publisher Summary This chapter discusses the cultural influences on handedness. Right-handers comprise the vast majority of the adult population. Judging from the depictions of hand use in the works of art and from the analysis of the design of weapons, tools, and other historical artifacts, they also would seem to have been the norm since prehistoric time. Handedness represents the end-product of a long and multifaceted biosocial process. The environmental role can be studied in a number of ways. One way is through direct observation of the development of hand use in the context of the social and cultural environment. Direct observations might reveal whether parents are encouraging this preference by their own actions. Observations also could be made at the preschool and school-age periods and in every social situation throughout the life span. Older children and adults can be asked directly whether their hand preference has been encouraged or discouraged, and with what result, and inquiries can be made of teachers and school administrators as to their policies and practices. Cross-cultural surveys of the prevalence of left-handedness offer another way to measure the environmental role. The reason is that, although all cultures are designed for the right-hander, the rules are applied more liberally, or flexibly, in some cultures than in others.

Cultural influences on handedness: Historical and contemporary theory and evidence.

Cross-sectional life span studies of handedness typically show decreasing percentages of left-handers in older age groups. In an article in Psychological Bulletin, S. Coren and D. F. Halpern (1991) argued that this age trend reflects the shorter life span of left-handers than right-handers. They presented 2 studies of their own providing what they regard to be direct evidence that left-handers, on average, die sooner than right-handers. They also proposed a variety of reasons for what they called left-handers' "decreased survival fitness." I discuss Coren and Halpern's reasons for rejecting a more conventional explanation of the life span data; the 2 studies that they offered in support of their argument; their analysis of other evidence they invoked to account for left-handers' putative decreased survival fitness; and, finally, new studies in which the longevity explanation was tested by more direct means than have been used thus far. I conclude that the case for the "decreased survival fitness" hypothesis cannot be sustained.

Do left-handers die sooner than right-handers? Commentary on Coren and Halpern's (1991) "Left-handedness: a marker for decreased survival fitness".

The androgen model of suicide completion.

L. G. Harris's (1993) critique of our hypothesis that left-handedness is associated with a shorter life span (S. Coren & D. F. Halpern, 1991) ignores the supporting statistical evidence, which virtually always shows an increased incidence of left handedness (or other left-sided laterality) associated with a wide range of health risk factors, including serious accidents, immune disorders, early onset breast cancer, alcoholism, smoking, some types of mental retardation, homosexuality, birth-related complications (e.g., resuscitation at birth, extremely low birth weight, Rh incompatibilities, multiple birth, breechbirth, and older maternal age), and selected categories of mental disorders

Vann Smith

Papers

Brain asymmetry predicts suicide among navy alcohol abusers.

Left-handed versus right-handed alcoholics; an examination of relapse patterns