In 2021, zookeepers at Japan’s Kujukushima Zoo & Botanical Garden were confronted with an unexpected mystery: Momo, a 12-year-old white-handed monkey housed alone, was pregnant.
This puzzling development prompted an extensive investigation to uncover the circumstances behind her conception.
The Initial Monkey Conundrum
Momo’s solitary living arrangement led staff to question how she could have become pregnant without an apparent male companion. The situation was further complicated by Momo’s protective nature, which made it challenging for keepers to approach her and her offspring for closer examination.

Unraveling the Monkey Mystery
After two years of meticulous investigation, zookeepers conducted a DNA test on Momo’s offspring, revealing that the father was Itō, a 34-year-old agile gibbon residing in an adjacent enclosure.
The breakthrough came with the discovery of a small hole. It was approximately 9 millimeters in diameter in the steel partition separating their enclosures. It is believed that Momo and Itō managed to mate through this aperture during their respective times in the exhibition area.
Implications and Preventative Measures
This unprecedented event prompted the zoo to reassess its enclosure designs to prevent unintended interactions between animals. The hole has since been sealed. Additionally, there are plans underway to introduce Itō into Momo’s enclosure to facilitate family bonding under supervised conditions.
Moreover, the resolution of Momo the monkey’s mysterious pregnancy highlights the complexities and surprises inherent in animal behavior. Yes, even zoo management! This definitely shows nature’s resilience. Zookeepers also need be vigilant in maintaining environments that prioritize the welfare of animals in human care.
A Curious Case That Captivated the Public
Momo’s story didn’t just intrigue zookeepers—it captured the imagination of people worldwide. The idea of a “mystery pregnancy” in a zoo sparked headlines, social media buzz, and plenty of speculation.
Some joked about a “miracle birth,” while others raised serious questions about animal welfare and enclosure security.

What started as an internal puzzle for the Kujukushima Zoo turned into a global talking point, reflecting how even scientific mysteries can become part of a broader cultural moment. In the end, the monkey case reminded us all that even in controlled environments, nature still has the power to surprise.