The developmental stages of a chimpanzee’s growth are divided into four phases and can be defined as: infancy, juvenility, adolescence, and adulthood (Hiraiwa-Hasegawa et al. 1984; Goodall 1986; Nishida et al. 1990).
Infancy (0–4 years old) entails being carried around by the mother, breastfeeding, being hugged when it is cold or raining heavily, and sharing an overnight bed.
Juvenility (5–8 years of age) comes after weaning is complete. The juvenile is physically independent, walks and climbs on its own, and makes and sleeps in its own night bed, but stays in close association with its mother. A juvenile is still under its mother’s supervision, especially when it comes to ranging.
Adolescence is marked by sexual maturity such as dramatic enlargement of the testes in males and tumescence of the sexual skin in females, but adolescents lack full adult body-size. Adolescent males are 9–15 years old, and females are 9–12 years old. They are still socially immature and usually are not permitted to join in adult grooming clusters.
Adulthood is when individuals are socially and physically mature. Males are 16 years old and over, and females are 13 years old and over. However, development is a progressive phenomenon, and as each individual’s pace differs, the age classification above is only a broad outline.