In 2021, zookeepers at Kujukushima Zoo and Botanical Garden in Nagasaki, Japan, were left completely puzzled when a 12-year-old female white-handed gibbon named Momo gave birth to a baby despite living without a male companion in her enclosure. The unexpected arrival raised questions about how the pregnancy could have happened, especially since Momo appeared to have no direct contact with any male gibbons.

For several years, the mystery remained unsolved because Momo was extremely protective of her newborn and did not allow zookeepers to get close enough to collect the necessary samples for DNA testing. However, as time passed, the zoo continued investigating the unusual situation in hopes of identifying the baby’s father.

Eventually, DNA testing provided a surprising answer. The father was identified as Itō, a 34-year-old male gibbon who lived in a neighboring enclosure. After examining the surrounding area, investigators discovered a tiny hole measuring just nine millimeters in the metal divider separating their living spaces. They believe the two animals managed to mate through this small opening when their display areas were positioned next to each other.

Following the discovery, zoo officials repaired the hole to prevent another unexpected encounter and considered plans to bring the small family together in a shared enclosure. Meanwhile, the baby gibbon was reported to be growing healthily. What initially seemed like an impossible mystery turned out to have a remarkably simple explanation, leaving both zoo staff and animal lovers amazed.