Ancient supernovae prompted human ancestors to walk upright

Cosmic energy bombarded by supernovae eight million years ago may have triggered a chain of events that eventually led to ancient humans walk on two legs, a study claims.

The research, published in the Journal of Geology, suggests that the supernovae initiated an avalanche of electrons in the lower atmosphere.

This atmospheric ionization probably triggered an enormous upsurge in cloud-to-ground lightning strikes that ignited forest fires around the globe.

These infernos could be one reason ancestors of Homo sapiens developed bipedalism -- to adapt in savannas that replaced torched forests in northeast Africa.

"It is thought there was already some tendency for hominins to walk on two legs, even before this event," said Adrian Melott, a professor at the University of Kansas in the US.

"But they were mainly adapted for climbing around in trees. After this conversion to savanna, they would much more often have to walk from one tree to another across the grassland, and so they become better at walking upright," said Melott.

They could see over the tops of grass and watch for predators," he added.

It is thought this conversion to savanna contributed to bipedalism as it became more and more dominant in human ancestors."