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1. Introduction
Hand laterality is a cognitive factor according to which a group of individuals (populations or species) differentially use one hand (left or right) to perform a task [1] or a group of tasks [2]. From a behavioural point of view, the importance of hand laterality lies in the fact that in humans it is the most developed functional asymmetry. Hand laterality seems to be an indicator of brain hemispheric specialisation, which is not exclusive to humans. It is present in species such as rats (Rattus norvegicus) [3], elephants (Elephas maximus) [4], humpback whales (Megaptera novaeangliae) [5], and crows (Corvus macrorhynchos) [6]. Actually, Rogers [7] suggests that all vertebrates share brain hemispheric specialisation. However, brain hemispheric specialisation seems to be also related in humans to linguistic functions. Therefore, its pattern of emergence and development throughout human evolution can provide insight into the evolution of human cognitive capacities.
In modern humans, 97% of the population is hand lateralised, and between 85% and 90% of individuals are right-handed [8]. However, several studies have found great diversity in the expression of hand laterality [9–17], which appears to be influenced by environmental and cultural factors [18] and by the motor actions involved in performing the task at hand [19]. Despite this variability, research in non-Western societies confirms the universality of hand laterality in the species Homo sapiens [20]. Results from three preindustrial cultural groups—the G/wi (Botswana), Himba (Namibia), and Yanomamo (Venezuela)—show right-hand dominance at the population level for all tasks and stronger preferences for conducts involving tools. Even when discounting the strong biases of Western educative influences [21], the pattern of right-handedness in modern humans emerges. This has led to the widely accepted belief that human hand laterality may be conditioned by biological factors [8, 22] with inheritable components [23, 24].
Therefore, most research suggests the existence of a genetic component for hand preference, although neither the inherited pattern nor the responsible gene or genes have yet been identified [25–27]. Two main genetic models [22, 28] propose that hand laterality and brain dominance for language depend on a single gene with two alternative alleles. Both models assume that the gene for laterality is unique and exclusive to human beings....