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Why are male orangutans usually much larger than females?

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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.

Male orangutans are significantly larger than females due to sexual dimorphism, an evolutionary adaptation driven by intense male-male physical competition for access to mates.1

In the wild, adult male orangutans are typically twice the size of females. This size disparity is a direct result of natural selection, which favors larger body size in species where males must fight to defend or secure females from rivals. In addition to their larger overall stature, adult males develop unique secondary sexual characteristics, such as prominent cheek pads and a large throat pouch used for vocalizing the "long call," which helps them attract receptive females and space themselves out from other males.21

While subadult males lack these striking features and are smaller than fully mature adults, they remain as large as or larger than adult females. This pattern of sexual dimorphism is a common evolutionary trait among primates where males compete for dominance and reproductive access.21