Senior citizens played an important role in the dramatic spread of human civilisation some 30,000 years ago, a study of the human fossil record has shown.

It found a five-fold increase the number of individuals surviving into old age in the Early Upper Palaeolithic period — around 30,000 years ago. This coincides with an explosive population growth of modern humans and the spread of archaeological artefacts that suggest the development of more complex social organization.

The grandmother hypothesis,” based on studies of African hunter-gatherer groups, suggests that infertile women are vital for successful child-rearing despite being unable to produce children themselves.

Other factors like diet, language, tool-making abilities and social bonding were also important to the success of modern humans.