The female becomes sexually mature at approximately 8 years of age, the male at approximately 11. The hierarchy within a troop is based on size and seniority and it determines mating. After 8 to 9 months, the mother gives birth to one baby, weighing 1.8-2.5 kilograms (4-6 lb.) Twins are rare. The young live with the mother for three years, with weaning commences at 1.5 years.