Yet linguistic research can trace back common words in human spoken languages for only about 30,000 years.
Researchers have traced asymmetrical control of language ability back two million years in the ancestors of humans. "The fact that handedness and language are both asymmetrical led me to think there must be a link," Dr Corballis says. That lopsidedness is now believed to be controlled by a gene, and if the gene is lacking, people are both less likely to be strongly right-handed and more likely to have speech problems such as stammering. In The Lopsided Ape (1991), Dr Corballis noted that humans are the only primates to be predominantly right-handed. Through studies of people whose left and right brains were split surgically to control epilepsy, scientists learned that the left side controls the hands and speech in more than 90 per cent of right-handed people and in more than two-thirds of left-handers. He started studying language through his previous work on how the two sides of the brain govern human behaviour. Hand signals might provide the crucial clue. Spoken languages must have evolved out of something. But Dr Corballis believes there has to be a better explanation. American linguist Noam Chomsky describes language as "based on an entirely different principle" to other forms of animal communication. Traditionally, language has been thought of as one of the defining characteristics of being human. But language, or the ability to convey non-instinctual ideas to others, dates back several million years - and ties us much more closely than had previously been thought to animals such as Sally.
He believes that "autonomous speech" - being able to make yourself understood in the dark without gestures or facial expressions - developed about 50,000 years ago. In a controversial book, From Hand to Mouth: The Origins of Language, Dr Corballis argues that language originated with gestures, not speech.
Professor Michael Corballis says he could understand what Sally meant as she held out her hand towards him or put her hand on her head to show she had had enough "conversation". By SIMON COLLINS, science reporter An Auckland University psychologist has established an instant rapport with a chimpanzee at Auckland Zoo named Sally.