For the first time, researchers have documented a behavior that had been thought unnatural, if not impossible: apes swimming.

The scientists captured on video two examples of apes that could swim quite naturally. The first was a young chimpanzee named Cooper, who not only figured out how to swim but could also dive underwater to retrieve items from the bottom of a swimming pool.

"We were extremely surprised when the chimp, Cooper, dived repeatedly into a swimming pool in Missouri and seemed to feel very comfortable," Renato Bender, a researcher at the University of the Witwatersrand in South Africa, said in a statement. "It was very surprising behavior for an animal that is thought to be very afraid of water." [8 Humanlike Behaviors of Primates]

The second ape was Suryia, an orangutan living in a zoo in South Carolina. Suryia was recorded swimming about 39 feet (12 meters) without assistance. Both apes use a modified breaststroke to navigate, which sets them apart from other mammals (including humans) that usually dogpaddle when forced to swim.

The breaststroke, the researchers speculate, might be the result of the apes' adaptation to life in the trees, where they use both arms and legs for moving, as opposed to walking on the ground, which more closely mimics a dogpaddle. The researchers also noted that zoos often use moats to confine apes — these zoos might want to rethink their primate enclosures.

This report of swimming apes recalls the controversial "aquatic ape" hypothesis of human evolution. First proposed in the 1940s, the hypothesis states that humans' semiaquatic nature differentiates us from apes: Living on the banks of bodies of water, humans eventually learned to swim and eat fish and other foods found only in water.

The aquatic ape hypothesis has been dismissed by most scientists, though it still has a handful of supporters, among them David Attenborough, well-known naturalist and television host. Attenborough recently spoke in favor of the aquatic ape hypothesis at a conference titled "Human Evolution: Past, Present and Future" in London, The Guardian reports.

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The researchers believe their videos highlight the need for further study of the ways that apes interact with water. "We still do not know when the ancestors of humans began to swim and dive regularly," researcher Nicole Bender of the University of the Witwatersrand said in the statement. "The behavior of the great apes in water has been largely neglected in anthropology."

The researchers' report was published July 30 in the online version of the American Journal of Physical Anthropology.

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