Abstract
In Experiment 1, we wished to determine whether a singly-housed adult male captive chimpanzee could discriminate the behavioral categories of sex and aggression. He was reinforced for selecting sexual rather than aggressive images on a touch-screen computer in a two-choice discrimination paradigm. He showed no discrimination after 24 sessions with non-human photos, but immediately selected human sexual images at above-chance levels. To explore whether this differential discrimination was due to a preference for human sexual images, he was presented with images of humans versus non-humans under non-differential reinforcement in Experiment 2. He preferred human photos if the images depicted sex, but not if the images depicted aggression. To further explore these preferences in Experiment 3 the chimpanzee was presented with images of genitalia of non-humans versus humans, genitalia versus eyes, and finally female versus male genitalia of both non-humans and humans, using non-differential reinforcement. The chimpanzee preferred human to non-human genitalia, and eyes to genitalia, but did not prefer female to male genitalia. This chimpanzee’s unusual social environment may have interfered with species-typical social preferences.
Highlights
In Experiment 1, we wished to determine whether a singly-housed adult male captive chimpanzee could discriminate the behavioral categories of sex and aggression
He was reinforced for selecting sexual rather than aggressive images on a touch-screen computer in a two-choice discrimination paradigm. He showed no discrimination after 24 sessions with non-human photos, but immediately selected human sexual images at above-chance levels. To explore whether this differential discrimination was due to a preference for human sexual images, he was presented with images of humans versus non-humans under non-differential reinforcement in Experiment 2
One can see that Joe was not more likely to select chimpanzee images, either when those images belonged to the reinforced category of sexual images, or the non-reinforced image of aggressive images
Summary
In Experiment 1, we wished to determine whether a singly-housed adult male captive chimpanzee could discriminate the behavioral categories of sex and aggression. Maki, Fritz, and England (1993) found no differences in atypical social behaviors shown by captive chimpanzees reared either by their mothers or by human caregivers, but did find that, if the chimpanzees were sent away to another institution before the age of three, they exhibited more abnormal behaviors. The majority of the research indicating deleterious effects of human-rearing or social isolation on primate development has been based on findings from rhesus macaques and chimpanzees. Aside from the negative impact on social and reproductive behavior, studies have shown that human-rearing may influence non-human primates’ spontaneous choice of photos under nondifferential reinforcement In these studies, captive chimpanzees and gibbons prefer photos of humans over members of their own species (Tanaka, 2003, 2007; Tanaka & Uchikoshi, 2010). The preferences for humans may arise over time, and may be demonstrated only in chimpanzees not raised by their own mothers
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