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Why do older male orangutans develop wide cheek pads?

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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.

In adult male orangutans, the development of wide cheek pads is a striking secondary sexual characteristic. These pads enhance the size of the head and are linked to increased levels of testosterone.1

This physical trait is part of the sexual dimorphism observed in the species, distinguishing fully mature adult males from subadult males, who lack these pads and remain smaller. The development of these features, along with a throat pouch used for vocalizing the "long call," plays a significant role in the orangutan's social structure by helping to space out males and attract sexually receptive females.1