Orangutans are sexually dimorphic (with two distinct gender forms): males are significantly taller than females are and weigh more than twice as much as females do. Both male and female orangutans range in color from bright orange to maroon or dark chocolate. The form of orangutans is well-adapted to an arboreal life-style. Their arms are very long and reach to their ankles when they stand upright. They have very long fingers and dexterous hands. Their feet are broad and look very similar to their hands, with long, grasping toes for climbing. They are the only primate with two distinct forms of mature males. Flanged males, with cheek pads, long hair, a large throat sac, and long calls, are intolerant of other mature males. Nonflanged males do not develop the secondary sex characteristics of flanged males: cheek pads, long hair, long calls, large size, and defense of territory. The nonflanged males are closer to females in body size. Both forms can impregnate females and contribute to the population's reproduction. The transition from unflanged to flanged is dependent upon complex social cues not yet fully understood. Like other great apes, orangutans have no tail, are large-brained, and are sapient (aware of themselves as individuals).