Figure 1.

Cumulative number of gesture types observed in the study groups, as a function of the number of gestures coded, separately for each species ((a) chimpanzees, (b) orangutans, (c) siamangs) and group (circles: chimpanzees in Atlanta; light and dark grey squares: orangutans at the Leipzig and Zürich Zoos, respectively; black crosses and black diamonds: siamangs at the Howletts Wild Animal Park, groups A and B, respectively; light grey asterisks and dark grey diamonds: siamangs at the Krefeld Zoo, groups 1 and 2, respectively).