Peru has more than 4, 500 registered burial sites, yet fewer than 2% of the bodies have been identified, according to the Peruvian Forensic Anthropology Team (Epaf), a non-government organisation.

BBC: Scarf of Hope to remember Peru's missing

"Take sex away and they don't have the chemical stimulants that give them a sense of well-being, " says Helen Fisher, a Rutgers University research scientist in anthropology.

WSJ: When He Says, 'More' and She Says 'No'

He also, as a former anthropology student, reflected on what it has been like to create a cultural myth which wins obsessive, almost quasi-religious interest from some fans.

BBC: Mark Lawson