Documentary setting out to explore same-sex behaviour in animals, which has been reported in more than 1,500 species and was even observed by the ancient Greeks and Egyptians. Traditional evolutionary theory cannot explain the purpose of being gay. So what are the animals up to? Scientists give their thoughts, including the difficulty of separating so-called `dominance" behaviour from pure sexual interactions, while a commercial sheep breeder reveals how some rams are exclusively homosexual, and no good to his business.