Why This Gorilla Prefers to Walk Upright

Louis the gorilla isn’t quite a germaphobe, says the zoo’s primate curator, but he’s definitely not a fan of mud.

Louis was just trying to keep his tomatoes intact and off the ground when he was caught on camera walking through his enclosure.

The 16-year-old western lowland gorilla is a favorite at the Philadelphia Zoo, and now he’s getting even more attention for his tendency to walk upright and over long distances.

“Some gorillas will walk upright when they have their hands full,” says the zoo’s curator of primates and small mammals, Michael Stern. He adds that most gorillas walk this way for a step or two. Louis, however, is often spotted taking longer strolls.

In the Facebook post showing the video of the gorilla earlier this month, the zoo suggested Louis was trying to keep his hands and food clean. Louis has since been branded as a “germaphobe” and a “clean freak”—two labels that are a slight mischaracterization, says the curator.

“I don't think he understands the germ theory of disease,” says Stern. “I would guess it’s the feel of the mud. They’re rainforest animals and they’re built to deal with mud, but they all have their own personalities.”

His Name Isn’t Mud

Stern adds that Louis’s keepers have noticed he tends to avoid mud, even when he’s not carrying food. A 2015 blog post from the Philadelphia Zoo noted:

“When caught out in a rainstorm, he'll run bipedally across the yard to seek cover, and when he accidentally steps in mud, he'll find a leaf or a paper bag and wipe his hand or foot off until they are clean again.”

The zoo has even rigged together a bridge made of fire hoses so that Louis can avoid the muddy puddles in his enclosure.

Of the gorillas at the Philadelphia Zoo’s troop, Louis is one of the largest, weighing in at 450 pounds and standing six feet tall. Despite his stature, he’s “probably the shyest,” says Stern.

The male, originally born in St. Louis, has been in captivity for his entire life. Few remain in the wild, where the species is critically endangered. Stern says his walking style is more likely a personality quirk than a byproduct of life spent inside a zoo. More commonly, gorillas walk on all fours, using their knuckles to help support their weight.

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Walk This Way

In 2011, a gorilla at a U.K. zoo also made headlines for walking upright. In an interview given to Live Science at the time, Indiana University anthropologist Kevin Hunt echoed the theory that the tendency to walk on two legs was a matter of personality.

Hunt additionally suggested the U.K. gorilla was mirroring the humans around him. The behavior also aligned with Hunt’s theory that humans evolved to be bipedal to more effectively gather food.

Stern notes that occasionally walking on two feet is probably more common for gorillas than people assume.

As for Louis, Stern says his keepers notice the behavior all the time. Now just happens to be the first instance the shy ape was caught doing it on camera.