The evolution of handedness in humans and great apes: a review and current issues.

Population-level right-handedness is a defining characteristic of humans. Despite extensive research, we still do not know the conditions or timing of its emergence in human evolution. We present a review of research into the origins of handedness, based on fossil and archaeological data for hand preference and great ape hand-use. The data show that skeletal asymmetries in arm and hand bones supporting a rightsided dominance were present at least in the genus Homo, although data are more robust for Neanderthals. The evidence from tool-use, production, and cave art confirms that right-hand preference was established in Neanderthals and was maintained until the present. The great apes can provide real-life models for testing the conditions that facilitate or enhance hand preference at both the individual and group levels. The database on great ape hand-use indicates that they do exhibit hand preferences, especially in complex tasks. However, their preferences vary between tasks, and while group-level biases have occasionally been reported, no human-like handedness bias has been found. We discuss the methodological problems encountered in these approaches. Shared problems include a lack of agreed terminology both within and between disciplines, small sample sizes, interpretation biases and a failure to replicate experiments. In general, there is a paucity of fossil material, with poor preservation hampering traditional metric methods. The archaeological data are often founded on unreliable methods. The primate database is plagued by the use of measures that could be inappropriate for revealing hand preference, and by methodological inconsistencies between studies. We emphasise the need to standardise the methods to allow between studies and species comparisons. We propose that when referring to "handedness" it is more appropriate to use the terms "hand preference" and "hand use", to avoid confusion with each discipline's own definition of handedness.