This gibbon became pregnant while living in isolation. How is that possible?

A Japanese zoo believes they’ve finally solved the mystery of how their female gibbon became pregnant while living alone in her enclosure.

The puzzle dates back to February 2021, when Momo, a 12-year-old white-handed gibbon at the Saikai National Park Kujukushima Zoo & Botanical Garden, shocked her keepers by giving birth.

But how? Momo lived separately from the zoo’s other male primates, reports Japanese publication Mainichi, their cages separated by bars and jagged chicken wire. Although the gibbons are put on display for the public, at no time would Momo have been exposed to an amorous male.

Could it be a case of immaculate conception?

Looking for an answer, zookeepers first collected stool and fur samples from her baby, which wasn’t an easy feat.

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“It took us two years to figure it out because we couldn’t get close enough to collect samples — she was very protective of her child,” Jun Yamano, the zoo superintendent, told Vice.

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It turned out the baby’s father was, indeed, one of the neighbouring apes — a 34-year-old agile gibbon by the name of Itoh.

They didn’t have video surveillance to rely on, so they turned to the next logical step: examining their enclosures for any security flaws that might allow the gibbons to have physical contact.

That’s where they solved the mystery: small holes in the wall of the exhibition area right in front of Momo’s cage. Measuring less than one centimetre wide, the holes in the perforated partition probably allowed the conception.

“We think it’s very likely that on one of the days that Itoh was in the exhibition space, they copulated through a hole,” zoo superintendent Jun Yamano told Vice.

Now that Momo and Itoh have gotten their “monkey business” out of the way, and welcomed new life into the world, the zoo says they’ve replaced the perforated wall with a steel plate. They also said they are going to try to move Itoh in with Momo and the baby.