Emulation, imitation, over-imitation and the scope of culture for child and chimpanzee

Abstract

We describe our recent studies of imitation and cultural transmission in chimpanzees and children, which question late twentieth-century characterizations of children as imitators, but chimpanzees as emulators. As emulation entails learning only about the results of others' actions, it has been thought to curtail any capacity to sustain cultures. Recent chimpanzee diffusion experiments have by contrast documented a significant capacity for copying local behavioural traditions. Additionally, in recent 'ghost' experiments with no model visible, chimpanzees failed to replicate the object movements on which emulation is supposed to focus. We conclude that chimpanzees rely more on imitation and have greater cultural capacities than previously acknowledged. However, we also find that they selectively apply a range of social learning processes that include emulation. Recent studies demonstrating surprisingly unselective 'over-imitation' in children suggest that children's propensity to imitate has been underestimated too. We discuss the implications of these developments for the nature of social learning and culture in the two species. Finally, our new experiments directly address cumulative cultural learning. Initial results demonstrate a relative conservatism and conformity in chimpanzees' learning, contrasting with cumulative cultural learning in young children. This difference may contribute much to the contrast in these species' capacities for cultural evolution.

Figure 1.

A taxonomy of imitative and emulative learning processes. Here, senses of emulation distributed through the social learning literature are distinguished and fall under the headings of object movement re-enactment, end-state emulation and affordance learning. Simpler forms of social learning, such as stimulus enhancement, are omitted here (see Whiten et al. 2004 for a full taxonomy), as are related forms of social influence, such as contagion (see Whiten & Ham 1992). For further explanation, see text, particularly §2b.

Figure 2.

Transmission of alternative foraging techniques within and across groups of chimpanzees (after Whiten et al. 2007). (a) Stab technique applied to foraging box, (b) alternative slide technique, (c) spread of stab technique (dark grey bars) within group B1, followed by spread across groups B2 and B3, and (d) spread of slide technique (light grey bars) within and across groups B4–B6. Each group was able to watch the performance of the preceding group through large windows. Fidelity of transmission was high.

Figure 3.

A simple model of tradition and adjacent learning zones. The tradition zone (2) is proposed to lie between two thresholds of task complexity as experienced by the species of interest. Below the first threshold, all or most individuals can master the task by their own efforts. Above the higher threshold, the task is beyond the species' capability. In the part of the tradition zone nearest Zone 3, only rare innovators can master the task but others may acquire it through social learning: such traditions will be relatively robust. In the part of the tradition zone near Zone 1, traditions may be relatively short-lived as more individual-level learning occurs. The transition between Zones 1 and 2 will therefore be graded.

Figure 4.

Matching to observed scenarios in full model versus ghost conditions (adapted from Hopper et al. 2008). Mean proportion (+s.e.) of matches to direction of door slide witnessed by children (grey bars), chimpanzees (white bars) and pigeons (black bars) in active model, passive ‘model’ with ghost manipulation and full ghost (no model) conditions. Mean values and s.e. for pigeon data courtesy of Thomas Zentall (2008, personal communication).

Figure 5.

Over-imitation in young children. Percentage of children copying highly visible, causally irrelevant actions of model in three different tasks, compared with baseline performance of comparable actions (after Lyons et al. 2007, with permission). See text for discussion. Black bars, observed adult; white bars, baseline. P < 0.001.

Figure 6.

Honey-dip task. (a–d) model; (e–h) child participant. (a) Dip technique: model holds door open with one hand while dipping tool into the box. (b) Retrieval of ‘star’ rewards. (c) Poke technique: model slides the door with left hand while poking bolt with right. (d) Model levers lid open using tool. (e) Child performing ‘dip’ technique. (f) Child retrieving rewards. (g) Child performing ‘poke’ technique. (h) Child levering lid open with tool.