#PICTURE OF CHIMPANZEE AND GORILLA TRIAL#
#PICTURE OF CHIMPANZEE AND GORILLA CRACK#

Conservatism, the disinclination to adopt an alternative behavior after already learning a successful technique ( Hrubesch, Preuschoft & Van Schaik, 2009), although seemingly detrimental, can sometimes be beneficial as it protects an individual from the risk of failure or danger. There is, however, mounting evidence of chimpanzees’ lack of flexibility when presented with novel problem-solving tasks in many experimental contexts, both in captivity and the wild (e.g., Hrubesch, Preuschoft & Van Schaik, 2009 Gruber et al., 2011 Manrique & Call, 2015 Harrison & Whiten, 2018), which some have argued explains their reduced complexity of material culture in comparison to humans’ (e.g., Dean et al., 2014). Similarly, through experimental work, Yamamoto, Humle & Tanaka (2013) demonstrated that captive chimpanzees could switch to a more efficient foraging technique when using straws to get a juice reward after observing a social partner use a more efficient method.

#PICTURE OF CHIMPANZEE AND GORILLA CRACK#

Wild capuchin monkeys have also been observed switching the type (size and weight) of stone tools they use to crack open cashew nuts in response to changes in the ripeness (i.e., hardness) of the nuts ( Luncz et al., 2016). For example, Sakura & Matsuzawa (1991) observed chimpanzees in Bossou, Guinea, flexibly substituting different materials to use as anvils when cracking palm nuts. Beyond what and where to eat, chimpanzees and other primates demonstrate flexibility in how they eat (i.e., foraging techniques, Sanz & Morgan, 2011 Luncz & Boesch, 2014). Experimental studies have also revealed that chimpanzees can flexibly switch foraging locations to optimize the value of rewards they obtain ( Van Leeuwen et al., 2013 Hopper et al., 2015). For example, dietary flexibility has been observed in numerous primate species, demonstrating their ability to adopt novel food sources and niches in the wild (e.g., Chapman, 1987), although rank and sex may impact their likelihood to do so ( Reader & Laland, 2001). Many primate species are highly flexible. We theorize that because the apes understood the causality of the task, they did not form habits and were not conservative.

All apes switched to a more efficient straw removal sequence even though their previously-successful, but now less-efficient, solution remained available. Next, we presented the apes with a new configuration of the same task that required the apes to remove fewer straws to obtain the reward.

There was individual variation in the consistency of straw removal patterns exhibited by the apes, but no ape developed an exclusive habit in the order with which they removed the straws, further indicating their causal understanding of the task.

#PICTURE OF CHIMPANZEE AND GORILLA TRIAL#

All apes spontaneously solved the task in their first trial and across repeated trials the majority of their solutions were efficient (median = 90.9%), demonstrating their understanding of the puzzle. To further explore how they solved the task, we also recorded the order in which they removed the straws, which allowed us to determine if habitual action sequences emerged. To first evaluate the apes’ causal understanding, we recorded the efficiency with which the apes solved the task (i.e., whether they only removed straws below the reward, ignoring redundant ones above it). We presented six chimpanzees and seven gorillas with a clear tube from which they had to remove straws to release a reward. We investigated if chimpanzees ( Pan troglodytes) and western lowland gorillas ( Gorilla gorilla gorilla) would show greater flexibility when presented with a causally-clear task.

We propose that such conservatism might be a result of task design and hypothesize that conservatism might be linked to primates’ lack of causal understanding in relation to experimental apparatuses. In contrast to reports of wild primates, studies of captive primates’ flexibility often reveal conservatism: individuals are unable to switch to new and more efficient strategies when task demands change.

Picture of chimpanzee and gorilla