Many identified differences in human longevity between groups lack conclusive explanations, such as why women have a greater life expectancy. Differences in life expectancy due to handedness are another puzzle: "Many studies report that left-handers have a shorter longevity than right-handers, and the present study may provide a possible explanation for that finding. In a Cardiac Rehabilitation Unit for the elderly with a mean age of 75.2 years the prevalence of left-handers was 16.7%. This latter value was significantly different from the 6.7% in controls of similar age. These data suggest that heart disease may be one reason for a reduced longevity among left-handers. Left-handers use the right hemisphere for movement, and unilateral activation of that hemisphere in the form of EEG desynchronization and deactivation in the form of EEG slow waves are both related to cardiac abnormalities." In the grand scheme of things these differences are unimportant: the greatest determinant of our future longevity is progress in the application of aging research.