A deeper understanding of the evolution of cooperation will come from investigations of what animals know about working together. A study with Asian elephants now adds to the literature on the subject.
We are cooperating right now. You are sharing in a communicative venture that is the product of two authors coordinating their views on a scientific joint effort, mediated by an editor and a publishing team. This is no small feat; it is the result of the evolution of complex cognition that might be uniquely human. But there is increasing evidence that the evolutionary roots of cognitively rich cooperation may be found in our closest relatives, chimpanzees and bonobos. In research reported in the Proceedings of the National Academy of Sciences1, Plotnik et al. propose that elephants (which are only very distantly related to humans) can cooperate as cleverly as these great apes. Such an independently evolved case could help us identify the evolutionary pressures that shape intelligent minds.
Plotnik and colleagues required pairs of elephants to work together using a procedure developed by primate researchers2, scaled to elephantine proportions. A single rope was threaded through a platform baited with food. Pulling one end with its trunk resulted in the elephant getting the rope but not the platform. It took two elephants pulling together to succeed.
Plotnik et al. did not stop there — nor did the elephants. The animals had to learn to wait for their partner when they were not released together. And if the partner had no access to the rope, the test subject did not pull at all. Two of the elephants found their own solutions to the problem posed by Plotnik's team, one by placing her foot on her rope end and letting her partner pull, the other by waiting at the starting gate for his partner before approaching the platform.
Plotnik et al. conclude that elephants (Fig. 1), like chimpanzees2,3 and unlike birds4, may understand the role of the partner in a cooperative enterprise. Elephants (and most chimpanzees) did not perform perfectly: at first, when their partner was delayed, they pulled their end of the rope regardless. Similarly, rooks (a member of the crow family) spontaneously pulled in the platform in pairs, but did not wait for their partner. But when the delay was built in gradually (a procedure not used with the birds), both chimpanzees and elephants quickly learned not to pull until the partner was there, and in the case of the elephants, only when the partner could reach his end of the rope.
This overt cooperation need not, however, require any special social cognition. Instead, the elephants might have learned to pick up on the cues in the environment that meant pulling would be worthwhile (the sight of another elephant with the rope 'in-trunk', or the feeling of tension in the rope), just as we might wait for a traffic light and coordinate our behaviour with it to our advantage. The elephants certainly made strikingly few errors, but they live in a conservation centre and have been trained to perform log-hauling, painting and even music-making for visitors. As such, they are trained to be trainable. Future tests, such as seeing how readily the elephants can learn to wait for a non-social cue, such as a green light, are needed to distinguish between what the authors refer to as “a well-developed propensity toward partner-oriented, deliberate cooperation” and a more general propensity to learn quickly.
Nevertheless, elephants and chimpanzees learned to wait with comparable ease, so are the authors right to claim that their cooperative skills are on a par? An important finding yet to be explored in elephants is that chimpanzees bring about the opportunity to cooperate by recruiting their partner, going beyond a learned recognition of favourable conditions.
In the 1930s, Crawford showed5 that if one chimpanzee was given such a glut of bananas as to be uninterested in the task, the other would attempt to engage her, for example by pulling on her hand. In one more recent study2, a chimpanzee recruited a human experimenter (but not another chimpanzee) by leading him to the apparatus. In another3, the researchers taught the chimpanzees to wait, but then required the animals to remove a bolt to release a partner when one was needed. This they did. The chimpanzees had not simply learned to wait to pull until their group mate had the rope in reach, but they had grasped the causal role of the partner. The ability to rapidly transfer knowledge learned in one context to perform a new behaviour is a useful test of cognitive flexibility.
Chimpanzees seem to know enough about their group mates to be able to use them as social tools. There is no evidence yet that elephants do. However, this might reflect the alien nature, to a human observer, of elephant communication. Plotnik and colleagues stress that it will take time to decode their low-pitched calls and subtle positional cues. Another new study6 describes how elephants led by mature females, but not younger ones, bunch around their young when they hear a male lion's roar. But these authors could not discern how the elephants coordinated their defensive stance.
Plotnik et al.1 have broadened our appreciation of how different animals cooperate. Testing the world's largest land animal was a mammoth undertaking, but by adapting experimental techniques used on other species, notably primates, they have allowed direct comparisons to be made. To see how evolution shapes minds for cooperation, future work should compare closely related species that have different social systems. Perhaps a propensity to 'tune-in' to another's behaviour is an adaptation to social living more generally, and need not require large brains. Even some fish, with their small brains, are able to coordinate their hunting efforts7. Further research on various creatures great and small will help us learn about how animals — including humans — understand and coordinate with each other.
Plotnik, J. M., Lair, R., Suphachoksahakun, W. & de Waal, F. B. M. Proc. Natl Acad. Sci. USA 108, 5116–5121 (2011).
Hirata, S. & Fuwa, K. Primates 48, 13–21 (2007).
Melis, A. P., Hare, B. & Tomasello, M. Science 311, 1297–1300 (2006).
Seed, A. M., Clayton, N. S. & Emery, N. J. Proc. R. Soc. B 275, 1421–1429 (2008).
Crawford, M. P. Comp. Psychol. Monogr. 14, 1–88 (1937).
McComb, K. et al. Proc. R. Soc. B doi:10.1098/rspb.2011.0168 (2011).
Bshary, R., Hohner, A., Ait-el-Djoudi, K. & Fricke, H. PLoS Biol. 4, e431 (2006).
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