According to a new study led by Dr Gillian Forrester of the University of Sussex, a predominance to be right-handed is not a uniquely human trait but one shared by great apes.
The study, published in the journal Behavioural Brain Research, analyzed hand actions directed towards either objects or individuals in chimpanzees, gorillas and children, and found that all three species are right-handed for actions to objects, but not for actions directed to individuals.
The results support a theory that human right-handedness is a trait developed through tool use that was inherited from an ancestor common to both humans and great apes. The findings challenge a widely held view that right-handed dominance in humans was a species-unique trait linked to the emergence of language.
“Humans have been tool users for 2.5 million years, while the current view is that language only emerged one hundred thousand years ago,” Dr Forrester said. “Our findings provide the first non-invasive results from naturalistic behavior, suggesting that language emerged as a consequence of left hemisphere brain regions that were already evolved to process regular sequences of actions. The structure found in language may have developed from pre-existing brain processes adapted from experience with tool-use.”
The team involved video sampling and coding of activities in individual groups of gorillas, chimpanzees and four-year-old children within their everyday environments. The simple and non-invasive methodology revealed aspects of brain function and organization without the need for a laboratory setting with expensive and invasive equipment or testing. Each observed hand action was coded as being directed towards either an inanimate object, such as sticks for apes and toys for children, or ‘animate’, such as touching others or self-grooming. The team found that in all groups there was a right-handed dominance only in actions towards inanimate objects.
“Human right-handedness is not species-specific as traditionally thought, but rather is context-dependent – a pattern that has been previously masked by less sensitive experimental measures. Our findings support the idea that both human and ape brains have this left hemisphere specialization directing the right side of the body for ordered sequences of behaviors, but that humans have been able to extend upon this neural architecture to develop language,” Dr Forrester said.
The study may help to further the understanding of language development in children.
Bibliographic information: Gillian S. Forrester et al. 2012. Human handedness: An inherited evolutionary trait. Behavioural Brain Research, published online 27 September 2012; doi: 10.1016/j.bbr.2012.09.037