Scientists claim swimming apes prefer breaststoke over doggy paddle

The first detailed observations of swimming chimpanzees and orangutans suggest that they, like humans, tend to swim using a form of breaststroke. The findings imply that we may owe our swimming style to our evolutionary past. Apart from humans, great apes usually avoid deep water for fear of unseen predators that might be lurking there, but anecdotal evidence shows that they will go for a dip if they feel safe enough. Cooper the chimpanzee and Suryia the orangutan are extreme examples of this. These two captive apes, raised respectively in Missouri and South Carolina, have thrown off any instinctive fear and taught themselves to swim in a swimming pool.



Footage taken by Renato Bender at the University of the Witwatersrand in Johannesburg, South Africa, shows that both of the apes instinctively opted for a version of breaststroke to keep afloat – that is, they moved their limbs out sideways from their bodies, roughly parallel to the water's surface. Suryia's limbs moved mostly alternately but Cooper often kicked with both hind limbs simultaneously, more like human breaststroke, says Bender. This behaviour is unusual because almost all other four-limbed mammals use doggy paddle, with their limbs moving vertically through the water directly beneath their body.

The footage also shows the apes were comfortable beneath the surface. Suryia opened his eyes underwater and could navigate visually, but Cooper preferred to keep his eyes covered, and used his hands and feet to feel for interesting objects. "You should expect deviation from doggy paddle in animals that, during their evolution, have had little contact with water and therefore almost completely lost the instinct to swim," says Bender. But why should apes, including humans, prefer breaststroke when we do take the plunge? Bender thinks it may come down to our tree-swinging past.


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Our shoulders and those of other apes have joints that can move in all directions instead of in just one plane, like the shoulders of most other mammals. That might make breaststroke the natural choice, says Bender. It is a careful analysis of swimming style, says Anne Russon at York University in Toronto, Canada, and fits well with recent evidence that great apes show a range of water-based behaviours. She thinks the evolutionary scenario sketched out by Bender could explain why the chimps and orang-utans adopt a form of breaststroke broadly similar to the stroke humans use – although tree-dwelling does not necessarily encourage primates to "forget" how to swim. "Monkeys I see often in Borneo are both excellent swimmers and are highly arboreal," she says.