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Why do orangutans have such long arms?

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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.

Orangutans possess the longest arms of all the great apes, an anatomical adaptation that supports their life as the largest arboreal animals. Because they spend more than 90 percent of their waking hours in the trees, these elongated limbs are essential for navigating the forest canopy.1

While orangutans typically move by scrambling through the trees using all four hands and feet, they also occasionally utilize brachiation—a form of locomotion where the animal swings from one hold to another using only its arms. Their arm length, combined with highly motile shoulder joints and hooklike hands, facilitates this specialized movement. Additionally, their flexible hip joints allow them to use their legs in a manner similar to their arms, enabling them to grip vertical tree trunks effectively as they move through the rainforest.2134