human history for thousands (perhaps millions) of years. At the beginning of the book, when mankind is about to achieve spaceflight, the aliens reveal their existence and quickly end the arms race, colonialism, racial segregation and the Cold War. 1960s In Star Trek, the Federation (including humans) has a strict Prime Directive policy of nonintervention with less technologically advanced cultures which the Federation encounters. The threshold of inclusion is the independent technological development of faster-than-light propulsion. In the show's canon, the Vulcan race limited their encounters to observation until Humans made their first warp flight, after which they initiated first contact, indicating the practice predated the Human race's advance of this threshold. Additionally, in the episode "The Chase (TNG)", a message from a first (or early) civilization is discovered, hidden in the DNA of sentient species spread across many worlds, something that could only have been fully discovered after a race had become sufficiently advanced. In Hard to Be a God by Arkady and Boris Strugatsky, the (unnamed) medieval-esque planet where the novel takes action is protected by the advanced civilization of Earth, and the observers from Earth present on the planet are forbidden to intervene and make overt contact. One of the major themes of the novel is the ethical dilemma presented by such a stance to the observers. 1980s 1986: In Speaker for the Dead by Orson Scott Card, the human xenobiologists and xenologers, biologists and anthropologists observing alien life, are forbidden from giving the native species, the Pequeninos, any technology or information. When one of the xenobiologists is killed in an alien ceremony, they are forbidden to mention it. This happens again until Ender Wiggin, the main character of Ender's Game, explains to the Pequeninos that humans cannot partake in the ceremony because it kills them. While this is not exactly an example of the zoo hypothesis, since humanity makes contact, it is very similar and the humans seek to keep the Pequeninos ignorant of technology. 1987: In Julian May's 1987 novel Intervention, the five alien races of the Galactic Milieu keep Earth under surveillance, but do not intervene until humans demonstrate mental and ethical maturity through a paranormal prayer of peace. 1989: Iain M. Banks' The State of the Art depicts the Culture secretly visiting Earth and then deciding to leave it uncontacted, watching its development as a control group, to confirm whether their manipulations of