Large babies 'shaped the development of modern human societies'

Human babies weigh proportionately more at birth than the newborns of any other primate species and this may have influenced the development of our society, according to a study.

A baby ape weighs an average of 3 per cent of what its mother weighs - this doubles to 6 per cent for baby humans.

Our earliest human ancestors most likely had big babies too and this could have helped define the shape of modern human societies, research suggests.

Big difference: The proportionately large size of human babies in relation to other primate species may have influenced the development of our society

Professor Jeremy DeSilva, an anthropologist at Boston University, said: 'Humans are strange, in all sorts of ways. We walk upright on two legs and our newborns are helpless.

'Our babies are unusually large. They have unusually large heads; they have unusually large bodies compared to other primates.'

The professor wanted to find out if species that were around millions of years before humans, such as Australopithecus, also weighed more.

A lack of fossilised remains of children temporarily proved to be a stumbling block, until Professor DeSilva decided to use adult skills to estimate the newborn's skull size.

'The whole expression that it takes a village is in part rooted in the fact that we have really big infants that are pretty helpless'

Using this method, he analysed a dozen Australopithecus skulls.

He told radio station NPR: 'So once you have the size of the head, there is what researchers have called "the 12 per cent rule".

'The 12 per cent rule says that the brain represents 12 per cent of the total body weight. It's not exactly 12 per cent - in fact, in the apes it tends to be more like 10 per cent.'

Even allowing for this difference, Professor DeSilva concluded that Australopithecus newborns were much closer to being 6 per cent of their mother's weight than to 3 per cent, like in apes.

He believes that rearing large babies has had a significant influence on human culture, even helping to stabilise communities.

He said: 'The whole expression that it takes a village is in part rooted in the fact that we have really big infants that are pretty helpless.

'If we wanted to get anything done, we have to hand them off.'

Professor DeSilva's study is published in the journal PNAS.