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Spontaneous prosocial choice by chimpanzees. Horner et al. Background - Altruism. Altruism commonly seen in humans Chimps closest biological relative Contradiction between observational and experimental studies Altruistic or empathetic behaviors seen observationally (sharing food)

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Presentation Transcript
background altruism
Background - Altruism
  • Altruism commonly seen in humans
  • Chimps closest biological relative
  • Contradiction between observational and experimental studies
    • Altruistic or empathetic behaviors seen observationally (sharing food)
    • Lack of consistent evidence for prosocial behavior in controlled experimental conditions
  • Two primary altruistic experimental methods
    • Giving Assistance Tests (GAT)
    • Prosocial Choice Tests (PCT)
background giving assistance tests
Background - Giving Assistance Tests
  • Choice between giving help or doing nothing
    • Giving an out-of-reach object for a human or conspecific
    • Provided a conspecific with a needed tool
  • Bonobos in particular show prosocial tendencies in GAT
  • Communication greatly increases chance of receiving needed help
    • Children similarly generally grant help only to vocal partners
background prosocial choice tests
Background - Prosocial Choice Tests
  • Subject chooses between two outcomes that are identical to self
    • One choice rewards only self, the other rewards self and a peer
  • Chimps have not shown consistent preference for the prosocial choice
  • However other monkeys (e.g. capuchin monkeys) have shown prosocial preference
background current study
Background – Current Study
  • Confounding factors may be responsible for lack of significant results
    • Complex testing apparatus
    • Distracting rewards
    • Limited contact between subject and partners
  • Horner et al.’s goal: reduce these extra factors
methods overview
Methods - Overview
  • Subject chooses a token from the bucket
  • Tokens represent either selfish or prosocial choice
  • Food given to either just subject, or both subject and partner, based on token
methods participants
Methods - Participants
  • 7 Adult female chimpanzees (6 in data)
  • All members of a long-established 12 chimp living group
  • All experienced in a token exchange program
  • Each chimp was tested with three different partners
    • One with a significantly affiliative relationship
    • One with a significantly negative relationship
    • One with a neutral relationship
  • Each subject given a preference tests, to control for any color preference in the tokens
methods contingency training
Methods – Contingency Training
  • Two participants were chosen and randomly designated as either the actor or the partner
  • Actor given a set of 10 tokens, 5 selfish and 5 prosocial (distinguished by differing color)
  • Experimenter requested them back one-by-one
  • Actor rewarded when giving any token back, partner rewarded when prosocial token given back
methods pct
Methods - PCT
  • Subject given tub filled with 30 tokens, 15 of each
  • Hands a token to experimenter, who puts token on easily visible platform, and replaces token in tub
  • Experimenter gives banana treat, wrapped in a noisy paper wrapping, to either the subject or the subject and partner
  • Partner can be easily seen and heard
methods control trials
Methods – Control Trials
  • Subjects were run through experiment again, with identical procedures until the PCT, including preference test and contingency training
    • A new color scheme selected for tokens
  • PCT the same, except for the lack of a partner
    • If a prosocial token chosen, experimenter still pretends to give a food reward to an imaginary partner
  • Prosocialv.s. selfish token
    • Bias towards prosocial choice
  • No partner control group
    • chimps choose randomly
  • Found no correlation for choices based off of previous behavior when roles were reversed
  • High ranking chimps found to be more prosocial than subordinate apes
  • No significant difference between related individuals vs. non related
  • No correlation between prosocial behavior and outside affiliation (grooming pairs)
results actor partner interactions
Results- Actor/partner interactions
  • Chimps interacted frequently
  • Behavior of partner categorized as:
    • Neutral
    • Attention-getting
    • Direct requests and pressure (DRP)
    • Partners engaged in the non-neutral behaviors more often following selfish choices by the actor
results actor partner interactions2
Results- Actor/partner interactions
  • Actors acted prosocial towards neutral partners, and even more prosocial towards attention-getting partners
  • Actors did not act differently from chance level for DRP partners
  • Chimps favor the prosocial option
  • Factors such as kinship, affiliation, dominance rank or reciprocity have no effects
  • Matches what chimps do in the wild when sharing a common goal
  • However, this study does have different results than other studies done in a lab
  • They believe this was due to
    • Close proximity
    • Wrapping the treats in paper
    • Avoiding complex apparatuses
    • Results also differ from popular suggestion that prosocial choices happen more often between related monkeys
    • They do acknowledge that chimps could be acting on reciprocity for events happening outside of the experiment
  • How do you think this could be controlled for?