This is the first in a four-part series looking at the energy revolutions that drove human history. In this programme Justin Rowlatt goes right back to the origin of our species two million years ago to explore how the mastery of fire by early humans transformed our metabolism, helping us to evolve our uniquely energy-hungry brains.

The physical evidence for early use of fire is frustratingly thin on the ground, according to archaeologist Carolina Mallol. But primatologist Jill Pruetz says she has learned a lot from observing chimpanzees interact with wildfires on the African savanna.

Research collaborators Rachel Carmody and Richard Wrangham theorise that our ancestors' unique ability to cook their food transformed the way our bodies access the energy it contains - something Justin seeks to test out by going on a raw food diet. The bounty of metabolic energy it delivered may have enabled us to become the formidably intelligent species we are today, according to neuroscientist Suzana Herculano-Houzel, transforming us into prolific hunters who conquered the world.

Producer: Laurence Knight