Americas 'settled in three waves'
Most indigenous Americans are descended from a single group of migrants, but later waves of people made important contributions
The biggest survey of Native American DNA has concluded that the New World was settled in three major waves.
Evidence from mitochondrial DNA (mtDNA), the genetic information in the mitochondria that power cells, supports descent from a single founding group of colonisers, who crossed from Siberia into America across the Bering land bridge.
This natural bridge appeared during the last Ice Age when sea levels were lower, allowing hunters to trek between the two continents.
