Life in a right-handed world is extraordinarily dangerous for the one out of 10 people who favor their left hand, a new study has concluded.
The study found that hidden "technological biases" against left-handed people may be causing millions of accidental injuries and deaths.In fact, the study concluded that accidents involving automobiles and machinery designed for the right-handed majority may literally decimate the left-handed population with advancing age.
Stanley Coren, professor of psychology at the University of British Columbia in Vancouver, said researchers are aware of a mysterious, age-related disappearance of left-handed people from the population.
Overall, left-handers account for about 10 percent of the world's population, a figure that scientists believe has remained essentially constant for centuries.
But studies show an unusually rapid age-related decline in the percentage of left-handers in the population.
Coren said left-handers account for about 13 percent of the population of people at age 20. But the percentage declines to only about 5 percent of people in their 50s. Virtually no left-handers seem to survive to age 80 and beyond, Coren said.
Authorities have examined and discarded one obvious explanation - increasing parental tolerance of left-handed children. Scientists once suspected that left-handedness is uncommon among older people because earlier in the century parents forced left-handed children to become right-handed. Now most permit the child to continue using the dominant hand.
"We believe that this absence of left-handers from the oldest age groups reflects higher biological and environmental risk," Coren said.
The study examined the frequency of serious accidents among 1,896 university students. The results, published in the current edition of the American Journal of Public Health, show that left-handers have an 89 percent higher risk of suffering an accidental injury serious enough to require medical care.
Left-handers faced a 20 percent higher risk of sports-related injuries; a 25 percent higher risk of work-related injury; a 49 percent higher risk of an injury in the home; a 54 percent higher risk of injury while using tools; and an 85 percent higher risk of injury while driving an automobile.
Coren noted that everyday implements, such as scissors, gearshifts and can openers are biased toward right-handed use. Traffic patterns are designed to utilize the clockwise turning bias of the right-hander. Saws, lathes and other power tools likewise are designed for right-handed use.
"Thus, to function in the right-handed world, the left-hander must either work with his non-dominant and less proficient right hand, or must adopt body postures and manipulation patterns that which are at variance with the design of the machines."
Coren said such activities place left-handers at an increased risk of suffering a variety of injuries, which may be a "significant" factor in reducing the longevity of left-handed people.
Other theories offer biological explanations for reduced longevity of left-handers.
Left-handedness, for example, sometimes is associated with stresses that occur before and at the time of birth. These include low-birth weight, prolonged labor, fetal deprivation of oxygen during birth and blood-type incompatibility between mother and fetus. Scientists theorize that such factors may have unrecognized, long-term consequences that reduce an individual's ability to survive.
Left-handedness also is associated with abnormally high levels of prenatal hormones, allergies and immune disorders