Turkana Boy, a nearly complete Homo erectus skeleton found near Kenya's Lake Turkana and dated to roughly 1.5 million years ago, is the specimen this episode rebuilds piece by piece. Anatomist Alice Roberts and a team of specialists work from the fossilized bones outward, using sea-floor sediment cores to reconstruct the drying, opening African landscape erectus had to survive. Modern heat-endurance tests and comparisons with human runners explain why losing body hair and developing sweat glands mattered once persistence hunting on open savanna replaced forest foraging. The reconstruction process is shown in detail, from skeletal measurements to a full-body model built in the studio, tracking how proportions, gait, and brain case shaped a species built for covering long distances in heat. Evidence for early fire use and for social care, including healed injuries that would have required help from others to survive, rounds out the picture of an ancestor whose body and behavior were already pointing toward later humans. Part of the Prehistoric Autopsy series.