Quote: Hockett and Ascher on signs and symbols

From “The human revolution”, by Charles Hockett and Robert Ascher, footnote 2 Hockett:1964:

Some recent discussions (e.g., Critchley 1960) try to deal with the emergence of language merely in terms of the contrast between "sign" and "symbol"; intentionally or not, these treatments give the impression that our ancestors acquired language in a single enormous leap. Anyone aware of the intricacy of design of every human language knows that such a leap was impossible; there had to be steps and stages. The contrast between "sign" and "symbol", first carefully discussed by Langer (1942), then adopted and developed by White (e.g., 1949, 1959), is too gross to serve.