Endurance, not speed, key to spread of human race

Mankind's switch from sprinter to endurance runner began in earnest in Europe and Asia during the last Ice Age, Sydney scientists have discovered.

And the explanation could be that having more efficient muscles helped people survive the cold, harsh climate when they moved to areas outside Africa.

Kathryn North, of the Children's Hospital at Westmead, said a common genetic variation influenced whether people were "sprinters or stayers".

All Olympic sprinters tested so far have an active form of a gene, which produces a protein called alpha-actinin-3 in the fast-twitch muscle fibres responsible for explosive bursts of power.

About 99 per cent of African people still have this original sprinters' gene, she said. "It's the normal ancestral state."

More than a billion people worldwide, however, have an inactive version of the gene and do not produce the muscle protein, Professor North has estimated.

This includes one in five Australians, she said.

This inactive version of the gene is more common among endurance athletes such as marathon runners and rowers, her team has shown.

For their latest study the researchers wanted to find out when the endurance version of the gene became so common, and what was the evolutionary advantage of losing the sprint gene.

They created mice without the gene and discovered they could run for about a third as long as normal mice with the sprint gene before becoming exhausted. They also found their muscle metabolism was more efficient.

To put a date on the spread of the inactive endurance version of the gene the team analysed DNA samples from 96 people from around the world.

The results, published in the journal Nature Genetics, showed the inactive form of the gene began to rapidly increase in frequency in Europeans and Asians about 15,000-33,000 years ago, during the last Ice Age.

Professor North said that having the endurance gene and more efficient muscles could have been an advantage in a cold climate where food was scarce. "It may have allowed them to adapt to the more hostile environments of Eurasia."