For many years, zoos have used water moats to confine chimpanzees, gorillas and orangutans. When apes ventured into deep water, they often drowned. Some argued that this indicated a definitive difference between humans and apes: people enjoy the water and are able to learn to swim, while apes prefer to stay on dry land.

But it turned out that this distinction is not absolute. Renato Bender, who was working on a PhD in human evolution at the School of Anatomical Sciences at the University of the Witwatersrand (Wits University), and Nicole Bender, who worked as an evolutionary physician and epidemiologist at the Institute of Social and Preventive Medicine at the University of Bern, have studied a chimpanzee and an orangutan in the US. These primates were raised and cared for by humans and have learnt to swim and to dive. Their findings have been published online on 30 July 2013, in The American Journal of Physical Anthropology.

Perhaps this ability to learn to like water and learn to swim, requires zoos to reconsider the common approach to confine these Great Apes in outdoor enclosures by water-filled moats. Although, until now gorillas in zoos broke out of their enclosure by jumping the surrounding - apparently too small - water-filled moats, but swimming across the moat to escape has not been documented yet.

The orangutan Suryia, who was filmed in a private zoo in South Carolina, also possesses this rare swimming and diving ability. Suryia can swim freely up to twelve meters. Suryia the orangutan swims with his limbs alternately forwards and backwards. These movements are highly divergent from swimming movements known from other primates. The researchers believe that this swimming style might be due to an ancient adaptation to an arboreal life. Most mammals use the so-called dog-paddle, a mode of locomotion that they employ instinctively. Humans and apes, on the other hand, must learn to swim. The tree-dwelling ancestors of apes had less opportunity to move on the ground. They thus developed alternative strategies to cross small rivers, wading in an upright position or using natural bridges. They lost the instinct to swim. Humans, who are closely related to the apes, also do not swim instinctively. But unlike apes, humans are attracted to water and can learn to swim and to dive.

(Source: Wits University media release, 14.08.2013)