An orangutan gives the thumbs up sign. (Story here.)
In his book Origins of Human Communication Michael Tomasello argues that language began as gesture alone and at some point vocalization joined in and eventually took over as the main linguistic “modality” although gesture has remained and important. (This blog has made four posts about Tomasello’s book [#1, #2, #3, #4]). The evidence offered for this scenario is threefold:
First, many ape gestures are individually learned and flexibly used, including in combination, whereas this is not true of ape vocalizations.
Second, many ape gestures are used with attention to the attentional state of the recipient, which is mostly not even relevant in ape vocal communication. …
It is also important evolutionarily that gestural communication is more sophisticated in apes (humans’ closest relatives) than in monkeys and other mammals, whereas something close to the opposite is true of vocal communication. [p. 35]
A paper in the September 11 issue of Cerebral Cortex, however, suggests that Tomasello may have been underestimating the nature of ape vocalizations.