Although there are 1.5 million species of animal on our planet, only three are known to go through the menopause – humans, pilot whales and killer whales.

Until now, little has been known about why killer whales are able to survive long after they've stopped reproducing.

But a new groundbreaking study suggests that they could go through the menopause as a way of reducing conflict between mothers and their daughters - and the same could be true for humans.

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A new study suggests that killer whales could go through the menopause as a way of reducing conflict between mothers and their daughters

REPRODUCTIVE CONFLICT Using a unique long-term dataset on wild resident killer whales in the Pacific Northwest, the researchers confirmed that older females are more closely related to their kinship group than young females are. The researchers suggest that this imbalance between generations means that when older and younger females reproduce at the same time, the calves of the old-generation females are 1.7 times more likely to die than the calves of younger females. Likewise, it is better for older females to compete less, and cooperate more. These findings suggest that the menopause evolved due to both cooperation and conflict in family groups. Advertisement

Researchers from the University of Exeter suggest that when older females do reproduce alongside their daughters, their young calves are more likely to die.

This means that it is evolutionarily advantageous for older females to stop reproducing themselves, and invest in helping their younger family members succeed.

Darren Croft, who led the study, said: 'Females of many species act as leaders in late life but continue to reproduce.

'Our new work provides a mechanism that can explain why old females stop [reproducing] - they lose out in reproductive competition with their daughters.'

Female killer whales usually start reproducing by age 15, and stop in their 30s or 40s.

But the animals normally live to be more than 90.

Previous studies have shown that older females play an important leadership role in the family, but this alone did not explain why they would stop reproducing themselves.

The researchers suggested that conflict between generations, known as the 'reproductive conflict', could provide an explanation.

Using a unique long-term dataset on wild resident killer whales in the Pacific Northwest, the researchers confirmed that older females are more closely related to their kinship group than young females are.

The researchers suggest that this imbalance between generations means that when older and younger females reproduce at the same time, the calves of the old-generation females are 1.7 times more likely to die than the calves of younger females.

Previous studies have shown that older females play an important leadership role in the family, but this alone did not explain why they would stop reproducing themselves

Likewise, it is better for older females to compete less, and cooperate more.

These findings suggest that the menopause evolved due to both cooperation and conflict in family groups.

The findings not only apply to killer whales, but also to humans.

Mr Croft told MailOnline: 'Our research suggests that menopause in both killer whales and humans has likely evolved due to very similar reasons which are a combination of the benefits that old females can give to their offspring and grand offspring in late life combined with the costs of competition between old and young females in the family group.'

When older and younger females reproduce at the same time, the calves of the old-generation females are 1.7 times more likely to die than the calves of younger females

The researchers now plan to use drones to look more closely at the behavioural interactions among killer whales.

Mr Croft said: 'We want to understand how old and young females are behaving in ways that impact the survival of their calves.

'For example, who are individuals sharing food with and when are they sharing it? Who is doing the babysitting? By getting a bird's eye view, we will be able to transform our understanding of the social lives of these amazing animals.'