Why don't chimpanzees in Gabon crack nuts?

Some populations of wild chimpanzees (Pan troglodytes) use hammers and anvils of stone or wood to crack open nuts for food. Others do not. The aim of this study was to ask why one non-nut-cracking population, in the Lope' Reserve, Gabon, lacks this useful form of tool use. We tested 10 hypotheses: (1) nuts are absent; (2) nuts are few; (3) nuts are unsuitable; (4) hammers are absent; (5) hammers are unsuitable; (6) anvils are absent; (7) anvils are unsuitable; (8) nuts are displaced by better food items; (9) intelligence is insufficient; and (10) knowledge is insufficient. All but the last are clearly falsified, leaving by exclusion the likelihood that Lope's chimpanzees lack the technology-knowledge of appropriate technique-to exploit this resource. Thus, the behavioral differences across populations of these apes are cultural and not environmentally dictated. This explanation is congruent with the distribution of chimpanzee nut-cracking across Africa.