‘Immaculate conception’ of female gibbon who became pregnant despite living alone in zoo explained

Staff at a zoo in Japan have finally solved the mystery of how a female white-handed gibbon named Momo managed to get pregnant despite living in an enclosure on her own.

Momo, who stays at the Kujukushima Zoo & Botanical Garden, in Nagasaki, became pregnant in 2021 and later gave birth.

However, staff were puzzled over how this came about as the 12-year-old is separated from neighbouring males by a set of sturdy bars and jagged chicken wire fencing. 

A post on the zoo’s Instagram account shortly after the baby gibbon was born read: ‘Just so everyone wants to know “who’s the dad” hasn’t been found out yet because we haven’t done DNA testing, but we found out the gender is male.’

Pictured: Momo (left) and her baby (right). Momo, who stays at the Kujukushima Zoo & Botanical Garden, in Nagasaki, became pregnant in 2021

Pictured: Momo’s baby. The zoo last week announced the identity of the father: Itoh, a 34-year-old agile gibbon

After calling in a researcher to analyse the DNA in hair and stool samples – collected last year from Momo, her child, and four potential fathers – the zoo last week announced the identity of the father: Itoh, a 34-year-old agile gibbon.

Explaining why it took so long to solve the mystery, Jun Yamano, the superintendent of the zoo, said: ‘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.’  

Momo and Itoh take turns to go on display to the public in the morning and afternoon, in an exhibition area directly in front of Momo’s cage. 

The two spaces are separated by a perforated board that supposedly stops the apes from mixing.

Yamano told Vice that the pair were probably able to mate through a hole in the wall measuring nine millimeters in diameter on one of the days that Itoh was in the exhibition space.  

Pictured: Momo (right) and her baby (left). Jun Yamano, the superintendent of the zoo, said: ‘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’

He also noted that this type of mating habit is unprecedented. 

In the wild, gibbons select their mates based on social behaviour, appearance and vocalisation. 

Generally, the zoo pairs gibbons using trial and error methods so the apes can get to know each other. 

Yamano said the zoo now plans to allow Itoh to share the space with Momo and their baby.

‘They have to get used to each other first. But hopefully they live together as one family,’ he said. 

The zoo has replaced the perforated partition board with a barrier with no openings, to further lower the chance of unwanted pregnancies, Yamano said.