Although wild chimps and orangutans will wade into streams, primatologists have never observed them swimming underwater in nature. However, two captive apes learned to swim, which may shed light on human evolution.

A chimpanzee named Cooper started his aquatic adventures in the bathtub of his caretakers’ home in Malton, Missouri. Cooper eventually graduated to the shallow end of the backyard pool. A pair of guide ropes helped Cooper as he developed his abilities, until the chimp could do his own version of the breaststroke.

In Myrtle Beach, South Carolina, trainers taught Suryia the orangutan to swim in the pool at the Institute for Greatly Endangered and Rare Species. Suryia started with a life vest, but now opens his eyes and grasps objects underwater without any assistance. Suryia now can swim approximately 12 meters (40 feet) across the pool.

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A paper in the American Journal of Physical Anthropology documented Suryia and Cooper’s aquatic achievements. The researchers noted that Cooper and Suryia’s abilities cast doubt on two hypotheses about why apes don’t swim in the wild. One belief held that apes lacked buoyancy, due to their fat-to-muscle ratio, and would sink. The other hypothesis was that apes lacked the ability to control their breathing enough to avoid inhaling water while swimming submerged.

Most primates don’t enjoy pool parties, and in the wild, only a few primates swim regularly. Proboscis monkeys take the primate watersports gold medal. Proboscis monkeys can swim approximately 20 m (65.6 ft) underwater and can cross rivers. Humans, though, are the most aquatic of the apes.

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IMAGE: Suryia the orangutan swims across a pool. (Screen grab from video provided by Renato Bender and Nicole Bender.)