Lightning triggered by spectacular cosmic blasts millions of years ago holds the key to why humans walk on two feet, according to new research.
The bombardment of electric storms forced our ancestors out of the trees by razing forests to the ground – making them forge a future down below.
It is what led to homo sapiens having hands free to build cathedrals, design rockets and snap iPhone selfies, say astronomers.
Lead author Professor Adrian Melott, of the University of Kansas, explained: “It is thought there was already some tendency for hominins to walk on two legs, even before this event.
“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.
“They could see over the tops of grass and watch for predators. It is thought this conversion to savanna contributed to bipedalism as it became more and more dominant in human ancestors.”
Exactly why and when our ancestors stood upright and started moving around on two feet is still shrouded in mystery.
The reason early humans, or hominins, abandoned a life on all fours has been debated by evolutionary experts decades. It is one of the defining traits of our species.
There is fossil evidence the iconic stance, not found in any other ape, began at least six million years ago.
Now, a cutting-edge study published in the Journal of Geology suggests for the first time that it was triggered by lightning-fuelled wildfires.
Prof Melott’s team say ancient exploding stars, or supernovae, gave ‘proto-humans’ no choice.
They began blitzing Earth with energy up to eight million years ago – peaking around 5.4 million years later.
It initiated an avalanche of electrons in the lower atmosphere – setting off a chain of events culminating in homo habilis.