The Raft review: A bizarre experiment to determine whether humans are naturally violent has predictably sexy consequences

In 1973, Spanish-Mexican anthropologist and human behavioural psychologist Santiago Genoves stuck 11 strangers on a raft and sent them on a three-month voyage across the Atlantic.

The ethically dubious experiment, which today sounds like the premise of a terrible reality TV show, is the subject of this gripping documentary, and was intended to determine whether humans left to their own devices were innately violent.

But what began as an well-intentioned academic study very quickly spiralled into garbage science, nautical orgies and tyrannical exploitation as Genoves, increasingly frustrated by a lack of results, begins to stir discontent among the crew. Seven of the surviving subjects reunite in the present day and aboard a reconstructed replica of the raft to tell their stories and compare their often divergent experiences, from the practical (how they went to the bathroom) to the psychological (their mounting mistrust of the meddling overseer).

Issues of gender, race and sex were pushed to the fore, and are raised again in the present day interviews. Genoves deliberately chose the most attractive people he could find to board the raft, from a range of different nationalities and backgrounds, and placed the women in the most important roles to cause tension among the men. But the mad scientist himself turns out to be the most intriguing character of all. His extensive notes from the voyage, read aloud by an actor, form the backbone of the piece, and describe a man less interested in neutral observation than in pitting the sexes against one another in a kind of Big Brother meets Waterworld showdown.

The Raft is an almost unbelievable story, artfully reconstructed.