Findings: Apes fingered in hand puzzle

July 4, 2003

UK scientists claim to have solved the puzzle of why more men than women tend to be left-handed. The answer, they say, is because our ancestors were that way, writes Natasha Gilbert.

Richard Byrne and Nadia Corp, of the Scottish Primate Research Group at St Andrews University, found that wild female chimpanzees had a right-handed preference and males a left-handed one.

This emerged as the primates manipulated the fruit of the woody vine Saba florida, a task that required strength, precision and asymmetrical hand use.

Although scientists have previously observed hand preferences in gorillas and chimpanzees in other tasks, such as tool use, this is the first time they have observed differences in hand preference between males and females in a species other than humans.

Professor Byrne told The THES that these findings suggested an early evolutionary origin of sex difference in human hand preference.

The study states: "If this pattern of lateralisation reflects the ancestral state, common to both chimpanzees and humans, it may explain why in modern humans, women tend more strongly to be right-handed than men."

The researchers suspect that this effect reflects sex differences within developmental constraints. They said that this explanation could similarly apply to the sex difference in modern human handedness.

Scientists had previously explained the tendency in modern human populations towards a preference for right-handedness but could not account for the differences of hand preference between the sexes.

They assumed that our pre-human ancestors were ambidextrous and postulated the occurrence of a single gene for right-handedness, thought to be unique to humans, that instigated a shift towards a higher frequency of right-handers. These findings will be published in the American Journal of Physical Anthropology.

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