Growing up as a gorilla.
A male becomes mature between 8 and 15 years. A female reaches sexual maturity at about age 8, but usually doesn’t have her first baby until at least 10. She usually conceives with in three estrus cycles. From then on, she spends most of her life pregnant or nursing, so gorilla sex is rare. The event usually quite ordinary; copulation last a few seconds, and achieved with a penis about 4cm long. During the few times a female is in estrus she may invite copulation from, or be pursued by, adult males. Mating behaviour and ‘sexual play’ is by subordinate males in common. Subordinate males may actually mate more than the silverback with subordinate females. The dominate silverback may tolerate this, but he usually monopolies a female during her peak estrus times. Presumably he can tell by a certain smell or other cue. All males seem to be aware of the signs of estrus and quarrels increase when a female becomes sexually receptive.
Pregnancy lasts for 8.5 months. It is difficult to detect in the field because gorilla bellies are always full of food! A new born infant has light brown skin and is highly dependant, rarely leaving arms of its mother in the first six months. Twins have been born to gorillas, but very rarely. The infant rides ventrally at first, clinging to the mother’s chest, but beings spending more time on her back as it matures. During the second year it becomes more independent and begins playing with others, interacting with the silverback, learning to feed itself. This period of experimenting with food is the main way that anew items are added to a gorilla group’s diet.
Infant gorillas interact a lot with adult males. Silverbacks often play with infants and have been known to ‘adopt’ an infant whose mother has died. Gorillas thus differ from many other primates in which child-rearing is left entirely to the females. It is probable that since dominate male in gorilla group defends access to estrus females in the group and he knows his “wives” and all the infants intimately, he takes a greater interest in them. Being the probable father of the infants, his caring behaviour presumably helps more of his children to survive, and they inherit the genes leading to paternal care.
