A genre of film embracing one or more of the following elements: speculative fiction, futurism, technology, and space travel. Early science-fiction was primarily concerned with man's exploration of the universe but soon found competition in a more paranoid strain of films in the 1950s. Fifties science-fiction dealt mostly with invasions of Earth by hostile aliens or giant radioactive mutations. Reactions to the testing of the A-bomb and Cold War paranoia were often reflected allegorically in these films. The 1960s and '70s saw a more hopeful strain of film emerge, as pessimism was briefly replaced again by the thrill of space adventure. Mounting ecological concerns, however, led to the 1970s "ecokill" cycle, featuring natural forces (mostly predatory animals) rebelling against their polluted environments. By the 1980s, this strain had evolved into the "dystopia" film, which dealt with the aftermath of an ecological or nuclear disaster, often speculating the formation of totalitarian governments or man's return to savage barbarism. As technology has increased, the ideological content of science-fiction film seems to have decreased, with special effects becoming an end in themselves rather than a means to make a point.