Animal News
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 behavior 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.
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 behaviors.
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.
No comments:
Post a Comment