The researchers pointed out in the 1988 study in Nature that stressors surrounding left-handed people’s birth impeded their longevity. They also suggested that genetics and hormones affected their immune system and that living in a right-handed society made them more prone to accidents. A 1991 article in Psychological Bulletin from the same researchers furthered these ideas, finding almost a 9-year difference in ages of death. However, a 1993 article in Psychological Bulletin challenged these studies, criticizing some of the problems with the sampling and statistical analysis.
Another 1993 study that was published in Neuropsychologia tested two hypotheses that might explain the discrepancy between right and left-handers in terms of old age. The elimination hypothesis suggested that the decrease in left-handedness in older people is because left-handers don’t live as long. The modification hypothesis indicated that changes in social norms affect the number of left-handers in different age groups.
The findings showed that the prevalence of left-handedness decreased as people got older, with 15.22% of young adults being left-handed, but only 1.67% of those over 80. However, there was an increase in the number of people who had switched from left-handed to right-handed writing as they got older. This supports the idea that changing social norms might explain the differences in left-handedness across age groups, rather than left-handers having shorter lifespans.