On the left, a grandmother known as GM2 nurses her granddaughter.

Two grandmother monkeys have been seen intervening to raise their own grandchildren, providing essential care including suckling the young.

The scientists who witnessed the behaviour say it is the first unambiguous example of such behaviour shown by a non-human primate.

The observations were made in a free-ranging group of Japanese macaques living in Katsuyama, Japan.

Details of the grandmothers' actions are published in the journal Primates.

The same group of wild, free-ranging Japanese macaques (Macaca fuscata) have been studied since 1958, so scientists have kept a record of the birth date and blood relationships of each individual.


It is very unusual for females who have not had their own young offspring for years to start to take care of other infants.

Dr Masayuki Nakamichi
Osaka University in Japan

One scientist, Dr Masayuki Nakamichi at Osaka University in Japan, has been studying the animals' social interactions for 30 years.

However, the behaviour of two macaque grandmothers surprised even him.

"We know that some monkeys… sometimes adopt infants. In most cases, it is females who have lost their own infants," Dr Nakamichi says.

"However, in the present cases, the old, probably post-reproductive mothers started to take care of their young granddaughters.

"It is very unusual for females who have not had their own young offspring for years to start to take care of other infants."

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