Pillars of family life, the community and often the workplace, grandmothers are a crucial component of human society – now researchers say they may also play an important role among giraffes.
Experts conducting a review of giraffe social behaviour say female giraffes live for about eight years after they can no longer reproduce – up to about 30% of their lives.
“Female adults continue to live long lives even after their child-bearing lives have finished,” said Dr Zoe Muller, a giraffe expert at the University of Bristol and a co-author of the research.
The trait used to be thought an oddity in nature, displayed only by humans and killer whales who are known to go through the menopause, with the latter spending about 35% of their life in a post-reproductive state. However other animals, including elephants, have also been found to live for many years after their fertility has declined or ended.
Muller noted that the phenomenon of a long post-reproductive life has given rise to the “grandmother hypothesis” – a theory, not without controversies – that suggests post-reproductive females aid with the survival and rearing of the offspring of relatives.
“Elephants are quite well known for having older matriarchs leading the group and post-reproductive females are known to be repositories of knowledge,” Muller said. “It has been shown that during times of drought or famine, if the group have older females around – so the grandmothers – the group has a much higher chance of survival.”
Similar benefits have been seen in orcas – killer whales – when grandmothers are present.
“Again it would imply that these older females are helping the group find resources in difficult times,” said Muller. “Essentially, complex social animals gain huge survival benefits from older females hanging around after they are done child-bearing.”
Writing in the journal Mammal Review, Muller and her co-author, Prof Stephen Harris, have weighed up the evidence, suggesting post-reproductive females, or grandmothers, may play a similar role in the social systems of giraffes.
“Giraffes traditionally have been viewed as very one-dimensional, very non-social animals that don’t really have a social system – they are just kind of aloof and flop about randomly,” said Muller.
But, she said, her own work, together with findings from the new review of evidence, suggests that is not the case. Instead, evidence of behaviours including cooperative care of young and female-bonded kin groups, suggests giraffes – like elephants – appear to have a complex social system and may actually live in a matriarchy.
“It hasn’t been proven, but it would be the most likely explanation because in these complex societies where we do get grandmothers sticking around, they usually transfer survival benefits to related animals along matrilineal lines – so they look after their sisters’ children, their daughters’ children, etc,” said Muller.
“It doesn’t necessarily mean that the males are submissive, but what it does mean is that the females form the core cohesive units of the social system – exactly the same as humans. When we were in hunter gatherer societies, our groups were composed of the women.”