New research has unlocked the importance of grandmothers in preserving the human species including our longevity and ability to form monogamous relationships.

The study by Australian and US researchers builds on an earlier theory of the ‘grandmother hypothesis’.

The theory suggests after their own childbearing years, grandmas freed up the next generation simply by helping to care for children.

Sydney University lecturer Dr Peter Kim told Ross and John grandmothers played a key role in human evolution.

‘It shows a strong advantage post-reproductive females in the population,’ he said.

‘What they do is they provide an extra hand.

‘One thing common among all primates is children are a lot of work, especially humans, as we all know they take a lot of effort.

‘Suddenly it becomes nicer to have multiple adults to take care of children.’

Listen: Why grandmothers are so important