Narrator: This is Science Today. A new study finds mutations in the mitochondrial DNA of human cells may have helped migrating, early humans from Africa adapt to colder, northerly climates. Douglas Wallace, co-leader of the University of California, Irvine study, says mitochondria are the power plants of cells, generating heat to maintain body temperature and synthesizing ATP, a chemical form of energy.

Wallace: These mitochondria are actually ancient symbiotic bacteria that entered our cells about 3 billion years ago and as a result, they have their own genome, their own DNA. Therefore, we've been able to reconstruct the origin and migration by actually examining the sequence variation of the mitochondrial DNA.

Narrator: Researchers discovered that a key change in the mitochondrial DNA of early humans may have resulted in successful adaptation to the cold.

Wallace: By changing this energy balance of their mitochondrial power plants from primarily work ATP production, to a high percentage of heat production to survive the cold winters.

Narrator: For Science Today, I'm Larissa Branin.