Chimpanzees breed all year round, whenever one of the females in the troop comes into season. Female chimpanzees have menstrual cycles very like humans and come into oestrus every 36 days, unless they are pregnant. They give birth about every three-four years, after a gestation period (time between fertilisation of the egg and birth of the baby) of 8 months. A female may be mated by all the males in a troop, regardless of their social standing, who show no sign of competition between themselves.
Usually only one baby is born - twins are rare. If it is the female's first baby, she often appears not to know quite what to do with it! However, by a combination of instinct, watching more experienced mothers with their babies, and learning, she soon starts to care for it. For the first 5 months of its life the baby chimpanzee is carried everywhere by its mother, and clings tightly to her fur. It begins to walk at about 6 months and weighs 9kg at a year old. The baby is dependent on its mother for at least two years, sometimes still riding on her back for periods at 4 years old. By this time, the mother will have another baby and the elder one has to fend for itself. It spends much if its time with chimpanzees of its own age and for the next 4 or 5 years learns where the best feeding places are and how to behave as a senior member of its troop.Read More: Chimpanzees and Humans