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The idea that language evolved from manual gestures rather than primate calls dates back at least to the 18th century, and was revived in modern form by the anthropologist, Gordon W. Hewes, in 1973. The main sources of current evidence are: (1) Signed languages invented by deaf communities share with speech the essential characteristics of language, including such properties as reference, generativity, grammar, and prosody; (2) Great apes in captivity are much better able to learn intentionaldoi:10.1511/1999.20.810 fatcat:7o7hbunv2ndzdn7tvi7zpdh7tq