GORILLA, the largest of the anthropoid (manlike) apes, inhabiting forest regions of West Africa from the Cameroons to the Congo river and represented by a somewhat different form in mountainous regions of the eastern Belgian Congo. The popular reputation of the giant ape (Gorilla gorilla) is largely due to the writings of the explorer Paul B. du Chaillu in 1861 and later. In 1903 a somewhat different type of gorilla was discovered in high mountains of the eastern Belgian Congo, where it thrives at an altitude of 1 o,000f t. and is protected from the cold by much longer and thicker fur than the western form. This mountain species is known as Gorilla beringei.
Though nearly related to the chimpanzee, the gorilla is a far larger and heavier animal, the males attaining a weight of 400 lb. or more, and a standing height of 51 feet. The naked skin of the face is black and wrinkled; the hair in general black, commonly with a reddish tinge on the crown and tending to become grey on the back in adult males. The animals inhabit dense forests, com monly in small family groups, feeding on fruits and tender shoots and occasionally raiding plantations. The West African gorillas construct sleeping nests in the branches of trees, which seem to be used chiefly by the females and young. These beds, commonly used only for a single night, are also sometimes constructed on the ground ; the American explorer Carl Akeley always found them thus placed by the mountain gorilla. Adult males, owing prob ably to their great weight, generally remain on the ground. The gorilla is shy and not usually inclined to attack man unless pro voked, in which case the males are extremely dangerous. A peculiar habit, mentioned by du Chaillu, and observed in all cap tive gorillas, is a rapid drumming on the chest with both hands. Comparatively few gorillas have been kept in captivity and most of these have survived for only a short time. They seem to react far less favourably to captivity than the chimpanzee, lacking the friendly curiosity, imitativeness and general social adaptability of that animal, and exhibiting in contrast a self-centred repression and lack of interest in their surroundings. A few examples, how ever, captured when quite young have remained fairly tractable up to the age of five or six years.
The American psychologist R. M. Yerkes, as a result of exten sive observations and experiments on the mentality of a young female mountain gorilla, found that this animal showed consid erable ability in the solution of problems involving the use of sticks as tools, stacking boxes to secure suspended food, and in experiments involving multiple choice and delayed response. Some insight, memory and anticipation of experience were clearly demonstrated. Though he cautiously avoids generalizing from a single case, Yerkes finds this gorilla, as "compared with chim panzees and orang-utans of like age . . . remarkably slow in adaptation and limited in initiative, originality and insight." (See