Most mammals, when they deign to take a dip, swim with a version of the doggy-paddle. The limbs move underneath the water, perpendicular to the water’s surface, in a running motion. But apes appear to swim a little differently–and much more like us.

Footage taken at the University of the Witwatersrand in Johannesburg, South Africa shows a chimpanzee and an orangutan swimming in a pool (joyfully, it must be said, even though the consensus is moving to ban the use of apes in research). Chimps are terrestrial and orangutans are arborial, but in a situation where it’s clear there are no predators lurking beneath the surface (because the water in the pool is clear), both happily took to the water and swam around.

And both used a sort of modified breast-stroke, somewhere between a front crawl (the type of stroke most often used in freestyle swimming competitions) and a breast-stroke. The arms aren’t working in tandem, like a breast-stroke, but they sweep the water, parallel to the surface rather than perpendicular. The apes aren’t running through the water, like the mammals that use a doggy paddle: they’re swimming.

It’s not clear why apes naturally use this motion to swim; it’s possible that our ball-and-socket shoulder joints make it more comfortable to move parallel to the water’s surface than to move perpendicular to it. (Most mammals do not have ball-and-socket shoulders.) Why is still a mystery, but it seems pretty clear that this is the natural choice for apes.

[via New Scientist]