Bonnie, K. E., & de Waal, F. B. M. (2006). Affiliation promotes the transmission of a social custom: handclasp grooming among captive chimpanzees. Primates, 47(1), 27–34.
Abstract: Handclasp grooming is a unique social custom, known to occur regularly among some, but not all populations of chimpanzees (Pan troglodytes). As with other cultural behaviors, it is assumed that this distinctive grooming posture is learned socially by one individual from another. However, statistical comparisons among factors thought to influence how a behavior spreads within a group have never, to our knowledge, been conducted. In the present study, the origination and spread of handclasp grooming in a group of captive chimpanzees was followed throughout more than 1,500 h of observation over a period of 12 years. We report on the frequency, bout duration, and number and demography of performers throughout the study period, and compare these findings to those reported for wild populations. We predicted that dyads with strong affiliative ties, measured by time spent in proximity to and grooming one another, were likely to develop a handclasp grooming partnership during the study period. A quadratic assignment procedure was used to compare correlations among observed frequencies of grooming and proximity with handclasp grooming in all possible dyads within the group. As predicted, the formation of new handclasp grooming dyads was positively correlated with the rate of overall grooming and proximity within a dyad. In addition, in nearly all dyads formed, at least one individual had been previously observed to handclasp groom. We concluded that affiliation and individual experience determines the transmission of handclasp grooming among captive chimpanzees.
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Lilienfeld, S. O., Gershon, J., Duke, M., Marino, L., & de Waal, F. B. (1999). A preliminary investigation of the construct of psychopathic personality (psychopathy) in chimpanzees (Pan troglodytes). J Comp Psychol, 113(4), 365–375.
Abstract: Although the construct of psychopathy has received considerable attention in humans, its relevance to other animals is largely unknown. We developed a measure of psychopathy for use in chimpanzees (Pan troglodytes), the Chimpanzee Psychopathy Measure (CPM), and asked 6 raters to complete this index on 34 chimpanzees. The CPM (a) demonstrated satisfactory interrater reliability and internal consistency; (b) exhibited marginally significant sex differences (males > females); (c) correlated positively with measures of extraversion, agreeableness, and observational ratings of agonism, sexual activity, daring behaviors, teasing, silent bluff displays, and temper tantrums, and negatively with observational ratings of generosity; and (d) demonstrated incremental validity above and beyond a measure of dominance. Although further validation of the CPM is needed, these findings suggest that the psychopathy construct may be relevant to chimpanzees.
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Brosnan, S. F., & de Waal, F. B. M. (2004). A concept of value during experimental exchange in brown capuchin monkeys, Cebus apella. Folia Primatol (Basel), 75(5), 317–330.
Abstract: We evaluated the response of brown capuchin monkeys to two differentially valued tokens in an experimental exchange situation akin to a simple barter. Monkeys were given a series of three tests to evaluate their ability to associate tokens with food, then their responses were examined in a barter situation in which tokens were either limited or unlimited. Capuchins did not perform barter in the typical sense, returning the tokens which were associated with the reward. However, females, but not males, showed a different response, preferring the higher-value token. This may indicate that they learned to prefer one token over the other rather than to associate the tokens with their specific rewards. This sex difference parallels previous findings of greater reciprocity in female brown capuchins than in males.
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de Waal, F. B. M. (2005). A century of getting to know the chimpanzee. Nature, 437(7055), 56–59.
Abstract: A century of research on chimpanzees, both in their natural habitat and in captivity, has brought these apes socially, emotionally and mentally much closer to us. Parallels and homologues between chimpanzee and human behaviour range from tool-technology and cultural learning to power politics and intercommunity warfare. Few behavioural domains have remained untouched by this increased knowledge, which has dramatically challenged the way we view ourselves. The sequencing of the chimpanzee genome will no doubt bring more surprises and insights. Humans do occupy a special place among the primates, but this place increasingly has to be defined against a backdrop of substantial similarity.
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