Collaboration encourages equal sharing in children but not in chimpanzees

Journal name:
Nature
Volume:
476,
Pages:
328–331
Date published:
DOI:
doi:10.1038/nature10278
Received
Accepted
Published online

Humans actively share resources with one another to a much greater degree than do other great apes, and much human sharing is governed by social norms of fairness and equity1, 2, 3. When in receipt of a windfall of resources, human children begin showing tendencies towards equitable distribution with others at five to seven years of age4, 5, 6, 7. Arguably, however, the primordial situation for human sharing of resources is that which follows cooperative activities such as collaborative foraging, when several individuals must share the spoils of their joint efforts8, 9, 10. Here we show that children of around three years of age share with others much more equitably in collaborative activities than they do in either windfall or parallel-work situations. By contrast, one of humans’ two nearest primate relatives, chimpanzees (Pan troglodytes), ‘share’ (make food available to another individual) just as often whether they have collaborated with them or not. This species difference raises the possibility that humans’ tendency to distribute resources equitably may have its evolutionary roots in the sharing of spoils after collaborative efforts.

At a glance

Figures

  1. Child study tasks.
    Figure 1: Child study tasks.

    a, Apparatus from study 1 with reward relocation mechanism as used in the collaboration condition (180cm×60cm×15 cm; adapted from studies with chimpanzees29, 30). In the collaboration condition, children had to pull both ends of the rope simultaneously to move the board towards the access holes in the front of the enclosure (solid arrow). Initially, two toys (marbles) were on each side (as shown), but as the children pulled the board closer, the black barriers slipped out such that one marble rolled to the other end, resulting in a 3:1 reward distribution (moving from right to left in this example; dashed arrow). b, In the no-work condition, the board was already in the front part of the apparatus, with no attached rope, when children approached it (same reward distribution, of 3:1). c, In studies 2 and 3, children had to move a block closer to move the marbles such that they would roll in front of the access holes. In the collaboration condition, children had to pull a single, long rope simultaneously to move a large block closer (solid arrow), moving four marbles at once, which then rolled towards the respective access holes (in this example, three marbles rolled to the left and one marble rolled to the right; dashed arrows). d, In the parallel-work condition, two smaller blocks (each with a rope attached) could be pulled individually, one by each child, causing the respective marbles to move and roll down the ramps. e, The no-work condition, without any work but with the same reward distribution, 3:1.

  2. Rates of equal shares.
    Figure 2: Rates of equal shares.

    a, In study 1, children in both age groups shared more often in the collaboration condition than in the no-work condition (F(1, 22) = 21.85, P<0.001). This was true even if only the results of the first trial in both conditions were used for the analysis (McNemar test, n1,0 = 0 (number of dyads sharing in the no-work condition but not in the collaboration condition), n0,1 = 6 (number of dyads sharing in the collaboration condition but not in the no-work condition), P = 0.03). b, In study 2, three-year-olds, but not two-year-olds, shared differently in the three conditions (significant age × condition interaction, F(2, 66) = 5.26, P = 0.008; main effect of condition, F(2, 66) = 12.87, P<0.001). Three-year-olds shared significantly more often in the collaboration condition than in either of the other two conditions (post hoc Scheffé tests, both P<0.05). The difference between the parallel-work and no-work conditions approached significance (P = 0.06). c, In study 3, children shared significantly more often in the collaboration condition as compared with the parallel-work condition (χ2(d.f. = 1,n = 24) = 6.0, P = 0.039). d, Across studies 4–6, chimpanzees did not share differently in the collaboration and control (no-work) conditions. See main text and Supplementary Information for details and additional analyses. Error bars, s.e.m.

  3. Chimpanzee study task.
    Figure 3: Chimpanzee study task.

    The apparatus was mounted in a booth between testing rooms. Two chimpanzees located in adjacent rooms (partition mesh not shown) had to pull the two ends of the rope simultaneously to move the upper-level platform in front of the access holes. During the movement, one of the unlucky individual’s rewards (grapes) fell onto the lower, see-saw, level and rolled to the lucky chimpanzee’s side. In the picture, the sliding platform (upper level) has been pulled almost to the front. This movement has caused one side of the platform to tilt, causing one grape from the right (initial location represented by the grape drawn in white) to roll to the left, falling through a hole and landing on the see-saw mechanism below. The see-saw could then be tilted by the chimpanzees (manner dependent on study and condition).

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Author information

Affiliations

  1. Max Planck Institute for Evolutionary Anthropology, Department of Developmental and Comparative Psychology, Deutscher Platz 6, 04103 Leipzig, Germany

    • Katharina Hamann &
    • Michael Tomasello
  2. Harvard University, Department of Psychology, 33 Kirkland St, Cambridge, Massachusetts 02138, USA

    • Felix Warneken
  3. Michigan State University, Department of Zoology, East Lansing, Michigan 48824-1115, USA

    • Julia R. Greenberg

Contributions

K.H., F.W., J.R.G. and M.T. designed the study and wrote the paper. K.H. and J.R.G. conducted the studies and analysed the data. F.W. supervised the research.

Competing financial interests

The authors declare no competing financial interests.

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Supplementary information

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  1. Supplementary Information (543K)

    The file contains Supplementary Methods, Results and Data for 6 case studies, Supplementary Figures 1-6 with legends, Supplementary Table 1 and additional references.

Additional data