From mouth to hand: Gesture, speech, and the evolution of right-handedness

Abstract

The strong predominance of right-handedness appears to be a uniquely human characteristic, whereas the left-cerebral dominance for vocalization occurs in many species, including frogs, birds, and mammals. Right-handedness may have arisen because of an association between manual gestures and vocalization in the evolution of language. I argue that language evolved from manual gestures, gradually incorporating vocal elements. The transition may be traced through changes in the function of Broca's area. Its homologue in monkeys has nothing to do with vocal control, but contains the so-called “mirror neurons,” the code for both the production of manual reaching movements and the perception of the same movements performed by others. This system is bilateral in monkeys, but predominantly left-hemispheric in humans, and in humans is involved with vocalization as well as manual actions. There is evidence that Broca's area is enlarged on the left side in Homo habilis, suggesting that a link between gesture and vocalization may go back at least two million years, although other evidence suggests that speech may not have become fully autonomous until Homo sapiens appeared some 170,000 years ago, or perhaps even later. The removal of manual gesture as a necessary component of language may explain the rapid advance of technology, allowing late migrations of Homo sapiens from Africa to replace all other hominids in other parts of the world, including the Neanderthals in Europe and Homo erectus in Asia. Nevertheless, the long association of vocalization with manual gesture left us a legacy of right-handedness.

Usage and comprehension of manual gestures in wild chimpanzees

“…In contrast to vocalisations, monkeys" Brodmann"s area is activated during both the production and perception of manual movements (Rizzolatti et al, 1996a, Rizzolatti et al, 1996b, Perrett et al, 1985. These neural structures underlying manual gestures in the great apes, are homologous with the language areas in the human brain, suggesting an important link between language and primate manual gestures, but not primate calls or other primate bodily movements (Corballis, 2003). Additionally, while many primate species commonly communicate with calls, facial expressions or bodily movements, manual gestures are typical only in humans and other great apes (de Waal, 2003).…”

“…One proposed modality of language evolution is that of gestural communication, defined as communicative movements of hands without using or touching objects (de Waal, 2003). While homologies between primate calls and language have been relatively well explored, we still have a limited understanding of how cognitive abilities may have shaped the characteristics of primate gestures (Corballis, 2003). In this Ph.D. research, I investigated the cognitive skills underlying gestural communication in both wild and language trained chimpanzees, with a special focus on the repertoire and the intentionality of production and comprehension.…”

“…Whilst we have a relatively good understanding of cognitive capacities underlying vocal behaviour in primates, such capacities in gestural domain are still poorly understood (Hewes, 1973, Corballis, 2003. However, it is important to understand what cognitive characteristics underlie gestural communication in primates.…”

“…However, it is important to understand what cognitive characteristics underlie gestural communication in primates. Whilst features of cognition make primate vocalisations an unlikely sole candidate for an evolutionary precursor to human language, it is possible that the cognitive skills underlying language evolution are present in the gestural modality of communication (Corballis, 2003, Hewes, 1973, Burling, 1993. This is because primates have a greater voluntary control over their limbs than their vocal output and more important similarities with human language can be observed in the gestural modality in many areas of cognition such as learning, symbolic communication and intentionality (Tomasello and Zuberbühler, 2002).…”

“…While many primate species commonly communicate with calls, facial expressions or bodily movements, only apes and humans frequently communicate with hands (de Waal, 2003, Pollick andde Waal, 2007). While the homologies between primate calls and language have been relatively well explored, we have a relatively limited understanding of how cognitive abilities may have shaped characteristics of primate gestures (Corballis, 2003). However, it is important to investigate how features of cognition and gestural communication in our primate relatives compare with the characteristics of cognition and communication evident in human language.…”