Stuart A. Altmann
Let us suppose for the moment that we are in a grove of acacia trees on the savannahs of East Africa. In the trees above our heads there is a group of the common African green monkey, sometimes called the vervet. Suddenly, a martial eagle swoops down on the vervets. The first vervet that sees the approaching eagle gives an alarm bark. At the sound of this vocalization all the vervet monkeys suddenly drop from the branches of the trees to the dense undergrowth, where they are safe from the attack of the eagle.
Here is a vocalization given by one member of a social group that is heard and responded to by other members of his group. Such vocalizations are obviously used for communication. But can we call this kind of communication a "language"?
On these same savannahs of East Africa, baboons, which are large, ground-living monkeys, are fairly abundant. At night, these animals sleep either in trees or on cliff faces. The small infant baboon sleeps huddled against its mother.
As the infant becomes older, however, the mother becomes progressively more reluctant to allow the infant to sleep next to her. This rejection by the mother seems to be a traumatic situation for the infant, and in the evening, as a group of baboons approaches their sleeping trees, the repeated cooing and screeching of a rejected infant can be heard. Sometimes the infant's calling is successful and the mother allows the infant to sleep next to her.
As a final example, in the rain forest of Central and South America there is a monkey, called the howler monkey, that pro-