Human spoken language may have evolved from a currency of hand
and arm gestures, not simply through improvements in the basic
vocalisations made by primates. This "gesture theory" of
language evolution has been given weight by new findings showing
that the meaning of a primate's gesture depends on the context
in which it is used, and on what other signals are being given
at the same time. Gesture is used more flexibly than vocalised
communication in nonhuman primates, the researchers found. A
proto-language using a combination of gesture and vocalisation
is therefore more likely to have given rise to human language,
than simply an improvement in the often involuntary
vocalisations that primates make, they say. Amy Pollick and
Frans de Waal at the Yerkes National Primate Research Center in
Atlanta, Georgia, US, tested the idea by looking at how strongly
gesture and vocal signals are tied to context in our closest
primate relatives - chimpanzees and bonobos. By observing
captive groups of bonobos and separate g