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215 principles of evolution we have had our answer. Of men elsewhere, and beyond, there will be none forever.””° Is there some universality in being and behavior that transcends evolu- tionary differences? Jack Cohen and Ian Stewart, who looked at this ques- tion in some detail in their book What Does a Martian Look Like?, proposed a test. If a feature rose more than once in the evolution of life on Earth (such as photosynthesis, locomotion, limbs, predation, flight), it is a universal. If it arose only once, it is a parochial. Mind-Stretcher. Is human-level intelligence a universal or a parochial? As far as we know, it has arisen only once on Earth, although dolphins, chimpanzees, and earlier hominids may not be far behind. Astrobiology as currently practiced does not allow us to imagine the spectrum of possibilities, concluded Cohen and Stewart. Our imaginations cannot conceive of anything truly alien.”° “There’s no limit to strangeness,” said Dyson. “The most likely form for E.T. is something we never imagined.””’ Intelligent aliens may not only be stranger than we imagine; they may be stranger than we can imagine. Our cultures constrain our visions. Science Fiction Images Each culture or subculture has an “image repertoire,” suggested one group of experts, a store of images and dramatic scenarios that its members share and draw upon (consciously and unconsciously) in trying to imagine the possibilities inherent in situations of which they have little or no experience. These images and scenes may be from cultural myths, literature, familiar artwork, popular imagery, and media. Most cultures now possess a body of speculation on possible encounters between humans and intelligent aliens, although these speculations may have no relationship to scientific data. Authors of written science fiction have been free to describe the most exotic forms. Television and cinema portrayals once were more con- strained to humanoids, particularly if the extraterrestrial had a speak- ing part. Now special effects can create any creature we imagine and give it a voice. Images of aliens and their behavior tend to reflect the era of human history when they are visualized. In the written science fiction of the nineteenth century, aliens often were seen as Darwinian competitors. More recently, American film and television depictions of extraterres- trials have oscillated from one extreme to another, from the weird and horrible invaders of the 1950s (“The Thing”, “Invasion of the Body Snatchers”) to the benign aliens of the 1970s (“ET”, “Close Encounters of the Third Kind”) and then back to the repugnant aggressor of the 1980s and 1990s (“V” and “Independence Day”). Images of Aliens