Radical theory suggests exploding stars lead to humans walking on two legs
- Scientists say surge of radiation led to lightning causing forest fires, making adaptation vital
It was the evolutionary leap that defined the species: while other apes ambled around on all fours, the ancestors of humans rose up on two legs and, from that lofty position, went on to conquer the world.
The benefits of standing tall in the African savannah are broadly nailed down, but what prompted our distant forebears to walk upright is far from clear.
Now, in a radical proposal, US scientists point to a cosmic intervention: protohumans had a helping hand from a flurry of exploding stars, they say.
According to the researchers, a series of stars in our corner of the Milky Way exploded in a cosmic riot that began about 7 million years ago and continued for millions of years more.
The supernovae blasted powerful cosmic rays in all directions. On Earth, the radiation arriving from the cataclysmic explosions peaked about 2.6 million years ago.
The surge of radiation triggered a chain of events, the scientists argue. As cosmic rays battered the planet, they ionised the atmosphere and made it more conductive.