In the 1990s, a high Himalayan cave in Upper Mustang, Nepal was discovered to contain 42 ancient people, buried on wooden bunk beds. American archaeologist Dr. Mark Aldenderfer believes there must be more burial caves, but the challenge is how to find them deep within cliff faces in the cold and inhospitable environment of the Himalaya. He enlists the world's best technical climbers to do the searching. Aldenderfer's theory is the funerary caves were carved out by the earliest people to have settled in the Himalaya. If he can find their remains and extract their DNA, he'll learn who these people were and what brought them to the toughest parts of the planet to live.
National Geographic's cameras capture the rare moments of discovery as they unfold. First, the 7-year-old on the expedition finds a human bone along a riverbed. Then, a series of burial caves are discovered above the riverbed, with human remains spilling forth from dangerously eroding caves. Bioarchaeologist Jacqueline Eng begins laying the bones out anatomically to count the number of individuals in the cave. The climbers, led by seven-time Everest mountaineer Pete Athans, recover bones from a total of 27 individuals: adult men, women, adolescents, even infants, along with their goats, cows and a horse. Wood inside the caves provides the clue that bunk beds must have housed the bones at one time.
Upon cleaning and taking painstakingly detailed observations of each bone, Eng discovers that 63 percent of the bones have cut marks on them, clear evidence of defleshing! Aldenderfer's quest takes an unexpected turn toward the macabre as he begins to trace the mortuary practices of Himalayan peoples, including the distinct sky burial rituals of the people of Upper Mustang today, where they cut up the flesh and bones of their dead and offer them to birds of prey. Could this modern practice, which dates back to the eighth century, be somehow related to the early peoples found with cut marks in Mustang's caves? Aldenderfer thinks so. Carbon dating reveals the cave people were from the fifthth century. Their practice of defleshing bones was likely a precursor funerary ritual that eventually led to the development of what is known as sky burial by ethnically Tibetan peoples today.
Another cave tomb discovery, however, reveals to Aldenderfer that Mustang was home to a mosaic of cultures, all practicing different means of disposing of their dead. This cave has no bunk beds and there's no evidence of cut marks on the skeletal remains. Aldenderfer discloses that the dead were put into pits with multiple layers of sticks and stones. By analyzing the ceramics inside the burial cave, Aldenderfer concludes that the people interred inside date to approximately 1000 BC. This culture, likely different from the defleshed peoples found a little further north, was one among many, Aldenderfer believes, that traveled along Upper Mustang's Kali Gandaki River Valley trade route. Aldenderfer's cave people and their differing mortuary practices prove that the Kali Gandaki was a major trade artery connecting migrating people, their goods and their evolving funeral rituals with the well-traveled and highly influential Silk Road, further to the north.