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Why can male orangutan hair look like a cape?

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An illustration of a female Bornean orangutan (Pongo pygmaeus) with long reddish-brown fur, hanging from tree branches with one arm extended upward and one leg hooked over a branch. A scale bar at the bottom shows lengths of 30 centimeters and 12 inches for size reference. — orangutan Female orangutans (*Pongo*) have the longest breeding interval of any mammal, giving birth on average once every eight years.

The appearance of a cape on a male orangutan is caused by the length of his hair. While adult males and some older adult females may have partially or entirely bare backs, the hair on a male can grow long enough to resemble a cape when he moves his arms.1

This feature is part of the physical development associated with sexual maturity in males. As orangutans reach full maturity, they undergo significant changes, including the development of prominent cheek pads and increased body size, which are linked to higher levels of testosterone.21