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. 2016 Apr 14;6:24528. doi: 10.1038/srep24528

Figure 1. The eight manipulation complexity categories found through the Guttman scaling method (increasing complexity from category 1 to category 8), and the number of species able to perform actions in a particular manipulation complexity category.

Figure 1

Copyright S.A. Heldstab, Pan troglodytes nut cracking K. Koops.