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Probabilities: Civilization, Technology, and Science Although the term civilization is used freely in the debate about the prob- ability of detecting extraterrestrial intelligence, there is no agreed defini- tion of what it means in this context. Our opinions about being civilized are highly subjective. Yet, we think that we will know the signs of alien civilizations when we see them. In a sense, we have ducked the issue by defining a civilization in terms of technologies that we can detect. That definition may exclude most civi- lizations elsewhere in our galaxy. Historically our term civilization came from ancient Rome, where to be a citizen meant to belong to the civitas, the Roman civil community—a very specific context.' In everyday usage, we think of civilization as a developed or advanced state of human society, or a particular stage or particular type of it. We often apply measures of societal complexity, eco- nomic, scientific, and technological development, religious or cultural dis- tinctiveness, and standards of behavior. Many prehistoric societies did not become what are generally termed civilizations. However, civilizations did arise independently in many dif- ferent parts of the world—Mesopotamia, the Indian subcontinent, China, Egypt, Mesoamerica, Peru. Some early civilizations developed in isolation, unaware of others. This was a very late event in human history. Yet, there clearly was a selective advantage for civilizations once they had arisen, because they continued to expand and to replace other ways of life—a process still going on.’ Mind-Stretcher. Are civilizations as we know them the highest form of social evolution? Or does some greater form lie beyond? We have become accustomed to assuming that certain steps are required for the evolution of civilizations. In our case, the first step may have been 89 Civilization