History, development and current advances concerning the evolutionary roots of human right-handedness and language: Brain lateralisation and manual laterality in non-human primates

摘要

This review highlights the scientific advances concerning the origins of human right-handedness and language (speech and gestures). The comparative approach we adopted provides evidence that research on human and non-human animals' behavioural asymmetries helps understand the processes that lead to the strong human left-hemisphere specialisation. We review four major non-mutually exclusive environmental factors that are likely to have shaped the evolution of human and non-human primates' manual asymmetry: socioecological lifestyle, postural characteristics, task-level complexity and tool use. We hypothesise the following scenario for the evolutionary origins of human right-handedness: the right-direction of modern humans' manual laterality would have emerged from our ecological (terrestrial) and social (multilevel system) lifestyle; then, it would have been strengthened by the gradual adoption of the bipedal stance associated with bipedal locomotion, and the increasing level of complexity of our daily tasks including bimanual coordinated actions and tool use. Although hemispheric functional lateralisation has been shaped through evolution, reports indicate that many factors and their mutual intertwinement can modulate human and non-human primates' manual laterality throughout their life cycle: genetic and environmental factors, mainly individual sociodemographic characteristics (e.g., age, sex and rank), behavioural characteristics (e.g., gesture per se and gestural sensory modality) and context-related characteristics (e.g., emotional context and position of target). These environmental (evolutionary and life cycle) factors could also have influenced primates' manual asymmetry indirectly through epigenetic modifications. All these findings led us to propose the hypothesis of a multicausal origin of human right-handedness.