Are age trends in adult hand preference best explained by developmental shifts or generational differences?

Hand use in the performance of six everyday activities was analyzed as a function of age in a sample of 654 adults. An unskilled grasping tasks showed the largest shift toward consistent right-handedness as a function of age; skilled manipulation tasks, such as writing, exhibited weaker age-related trends. Analysis of individual preference patterns showed decreases in mixed right hand use (defined as a right-hander who occasionally uses the left hand) and increases in consistent right hand use in older adults. There was also a weaker age-related reduction in mixed left hand use but the numbers of consistent left-handers remained a small, constant percentage of the sample across all age groups. These results are congruent with the predictions of two developmental hypotheses offered to explain trends in adult hand preference. These are, first, a postulated age trend toward hand preference consistency and, second, a practice effect related to an environment arranged to favor right hand use.