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Signing between chimpanzees was systematically sampled. Four of the five chimpanzees in this group had had 4–7 years of complete immersion in American Sign Language (ASL) when they were being home reared (Gardner & Gardner 1971:125–127). It was found that the chimpanzees signed to each other, integrating their signing interaction into their nonverbal communication. Eighty-eight per cent of all signs reported fell into the social categories of reassurance, social interaction, and play.
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Fouts et al. (1984) studied this question.
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