The Chimp Paradox Pdf.37
Emmanuelle Riker
Greater neuroanatomical variability among male chimpanzees may reflect selection, since most of the relevant sulcal measurements are heritable (table 1; electronic supplementary material, tables S1 and S2). If sulcal surface areas represent investment in the size of related cortical areas, and therefore certain cognitive abilities, disruptive/balancing selection on male behaviour may lead males to vary more than females in the size of related sulci. It seems likely that male chimpanzee reproductive tactics have been subject to disruptive/balancing selection, allowing a variety of male behaviours to increase reproductive success and resulting in the production and maintenance of multiple behavioural phenotypes [52]. This may be reflected in our results, since the sulci that are more variable in male chimpanzees may be involved in cognitive abilities that are associated with direct intrasexual competition (i.e. combat), possessive mate guarding and/or consortships.
For example, the STS is involved in social information processing in humans and other primates [72,73]. Interspecific differences in STS morphology are suggested to reflect socio-cognitive differences [74,75], and experimental studies suggest that living in larger groups increases grey matter (GM) in the primate mid-STS [76]. In addition, the orbitofrontal cortex is activated during face-matching tasks in chimpanzees [73], the lateral occipital cortex is activated by faces and other objects in humans and chimpanzees [77,78] and the superior parietal sulcus is associated with visuomotor attention in humans [79,80]. While males using different mating strategies are likely to differ in their socio-cognitive and combat abilities, females may not be expected to show as much variation. Accordingly, greater male variability at the superior temporal, fronto-orbital, occipital lateral and superior parietal sulci may reflect disruptive selection on male social and visual information processing skills, which may be under stabilizing selection in females.
In addition to the effects of selection, male chimpanzees may exhibit more neuroanatomical variation since they have longer developmental periods [87]. While female growth slows at around 10 years old, male growth continues until 13 years old [87]. Furthermore, female chimpanzees wean their daughters earlier than their sons [88,89]. This leaves males exposed to additional environmental effects that may influence condition-dependent traits, such as cognition (e.g. [51]). Notably, maternal glucocorticoid concentrations during gestation impact the HPA axis function of male offspring more than that female offspring [90], and males exhibit higher variability for other traits that are likely to be influenced by condition (e.g. body size [87]).
Owing in part to their complex social life, nonhuman primates, and chimpanzees in particular, have been the focus of intense scrutiny with regard to the psychological mechanisms underlying prosocial acts. A number of candidates for prosocial behaviour have been observed in the wild. Chimpanzees risk injury by going on border patrols, come to the aid of each other in conflicts, affiliate with victims of conflicts, groom each other and share food3,4,5,6. Even more spectacular examples of potential prosocial behaviour have also been observed, such as adoption of orphans and anecdotal accounts of rescues7,8,9. However, it is difficult to infer intentions from observations alone, particularly anecdotes10.
The key finding is that there was no difference between the two groups of chimpanzees. They were just as likely to release a peg to prevent access to food (NO-GO group) as they were to provide access (GO group). Response rates in both groups declined over time in experiment 1. After personal experience with the apparatuses, chimpanzees only released the peg when doing so resulted in them getting food for themselves. Stimulus enhancement can fully account for apparent prosociality in chimpanzees; prior evidence for prosocial behaviour may have been by-products of experimental designs, producing an illusion of helping in our closest living relatives.
These findings reconcile studies in which chimpanzees did not show signs of prosociality with those that did, and highlight the similarities between helping and sharing. In studies of active food sharing, chimpanzees failed to show a preference for prosocial outcomes when given a choice between outcomes that benefitted a conspecific from those that did not19,20,21,22,30. Some studies did report evidence for food sharing24,25,31. However, prosocial choices occurred at a fairly low rate, raising questions about how prosocial the subjects were. More critically, each of these studies is open to alternative explanations. In House et al.24, chimpanzees only showed weakly prosocial choices in a GO paradigm in which there was only one piece of food that could be delivered despite showing no prosocial preferences in other conditions. In a series of experiments by Claidiere et al.31 chimpanzees were faced with paired choices, one of which was mutually beneficial and one which was purely selfish; results were inconsistent and subjects failed knowledge controls. Perhaps the strongest positive evidence for sharing in an experiment comes from Horner et al.25 However, in this token exchange study, in which subjects preferred to exchange coloured tokens with an experimenter for wrapped food for both themselves and a partner, the results can be explained by a conditioned preference for the sound of food being unwrapped45; furthermore, there were no controls for task comprehension.
Instrumental helping studies in chimpanzees have shown more consistent evidence for prosociality, but here as well, alternative explanations have not been ruled out. First, the distinction between helping and sharing is not as clear-cut as has been suggested37,38,39. All instrumental helping studies with conspecific recipients involved delivering food or the means to get food33,35,36,46,47,48, blurring the distinction between sharing and helping. In the one direct test comparing prosociality rates when food or non-food items were delivered, there was no difference, showing that food delivery does not specifically impede prosocial behaviour36. The most highly cited evidence for helping in chimpanzee comes from experiments in which subjects hand objects back to human experimenters32,33. However, the chimpanzees had prior experience with handing objects back to their caregivers and were reinforced intermittently for this behaviour. A variable reinforcement schedule such as this produces persistent responding and it is not surprising that it generalized to a similar context in testing. Even though the behaviour of handing objects to humans was not intentionally trained for those studies, the prior learning history of the subjects has to be taken into consideration. When training is an explicit part of the experimental procedure, caution is needed in interpreting the results. In one study, chimpanzees that had been trained in symbolic use transferred food to their partners49. However, explicit training through standard shaping and training produced similar results in pigeons50, highlighting the importance of flexible behaviours in response to novel circumstances35. Other, more recent, helping studies35,36,46,48,51 can be explained by social tool use (giving a tool to a partner to get food for oneself), responding to solicitation (begging), or task persistence whenever food was visible, calling into question prosocial motivations.
Almost all prior food delivery (sharing) and instrumental helping studies have involved training in which actors first learn through personal experiences the results of their actions. While helpful in demonstrating that the animals have learned the task contingencies, this can create an expectation for getting rewarded in the test context. While it is important to demonstrate task understanding, this could be done after testing, or between tests of naïve then trained subjects as done here (ABA design). By giving chimpanzees the opportunity to observe the consequences of their actions on others before giving them personal experience mitigates the food expectation while still demonstrating task comprehension. Chimpanzees are able to learn through others by observing them72, so there is no reason that they could not learn to help, or hinder, others solely on the basis of observed outcomes.
We tested 13 chimpanzees with three recipients (16 chimpanzees overall, see below). These animals were rescued from illegal wildlife trade and kept at the Ngamba Island Chimpanzee Sanctuary, a forested island in Uganda. The research was approved and reviewed by the local ethics committee of CSWCT (Chimpanzee Sanctuary and Wildlife Conservation Trust), the organization running the Chimpanzee Sanctuary in Uganda, as well as UWA (Ugandan Wildlife Authorities) and UNCST (Ugandan National Council for Science and Technology). The chimpanzees live freely on the island, and come in at night to the sleeping rooms where they were tested in the morning. Participation was voluntary and after testing the subjects re-joined the rest of the group. They were not food or water deprived. Subjects had previously participated in studies on cooperation and helping33,36,75,76,77,78,79, but the current setup involved a novel apparatus. For further details on the subjects, see Supplementary Table 1. These studies took place in the summer of 2011.
Eleven chimpanzees from experiment 1 participated as actors in experiment 2; two from the NO-GO group failed to pass the training phase (Nkumwa, a female; and Kisembo, a male). The GO group consisted of six individuals (three males) and the NO-GO group had five (three males). The same three chimpanzees were used as recipients (Supplementary Table 1).
So that was the basis of the model, two thinking and interpreting of the brain, tapping into the entire brain and leading on how they see the world and what their agenda is. And they can often be similar or very disparate. And then the middle of the brain, just simplifying it as being massively complex computer system, which supports either of them depending on which one you want to use. But we have to then tidy the computer up regularly if our chimp brain puts in silly thoughts or silly feeling that are destructive or unhelpful beliefs, which will then influence the way we operate.
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