Gorilla Research at the Cognitive Evolution Lab
Next to the chimpanzees and the bonobos, gorillas are our closest living relatives. Thus, they provide a unique opportunity to explore how the human mind evolved, and to test the idea that we both evolved from an ape-like mind, and then deviated from this mind in important ways. We are fortunate to be able to work with a gorilla population and the terrific staff at the Franklin Park Zoo.
We are currently involved in two main projects with this gorilla population:
1) Economic decision-making, and 2) the perception of intentional and goal-directed actions.
1) Economic decision-making
It is clear that humans engage in a wide variety of computations when they evaluate whether the distribution of resources is fair, whether they should take an immediate but small reward or wait for a larger one in the future, and whether they should engage in risky behavior to maximize potential gains or go for a safe bet that is less profitable but secure. What is less clear, but currently of great interest in the study of comparative cognition, is the extent to which these capacities are shared with other animals.
We are building on the successes of recent studies of chimpanzees and capuchin monkeys in studying these phenomena to extend the comparative approach to gorillas. There are two reasons to take this perspective. First, given how little we know about economic decision-making in animals, quantitative empirical studies are sorely needed. Second, and more significantly, if we want to understand how economic decision-making evolved, and in particular, the selection pressures that shaped these capacities, a broad comparative perspective is necessary, exploring species living in similar and different socioecological conditions. Unlike the chimpanzees, who live in large fission-fusion societies, or the capuchins, who live in stable multi-male and multi-female societies, gorillas live in small harem societies. Gorillas are largely terrestrial, whereas chimpanzees combine terrestrial and arboreal living, and capuchins are largely arboreal. Further, whereas chimpanzees and capuchins are omnivorous and use tools in the wild, gorillas primarily forage on plant matter, and have rarely been seen using tools in the wild. These social and ecological differences may well play a role in sculpting their psychology, and in particular, in guiding their economic choices. To this end, we are currently running experiments looking at their capacity to delay gratification, to avoid or engage in risky decisions, and to distinguish between intentional and accidental outcomes.
2) Perception of intentional and goal-directed action
When someone moves, and we notice their movements, our brains immediately run a computation that provides meaning to such movements. That is, we don't simply see body parts moving in some coordinated fashion, we see an individual with presumed goals and intentions. Over the past decade, studies of human and monkey brain function have revealed a system that provides meaning to action by mirroring. Specifically, one way in which we see, and other primates appear to understand, another's actions is by simulating what we would do. Thus, on this view, action and perception of action are one and the same.
We are running experiments with gorillas to better understand how they perceive actions, and specifically, which features of an action they use to decide what the actor intends, and what his or her goal is. For example, if an actor grasps one of two containers, do gorillas perceive this as goal-directed and communicative, and fundamentally different from an actor who merely flops his hand onto a container? Do gorillas appreciate that some actions that might initially appear irrational gain rationality when environmental constraints are considered? For example, though it may initially appear bizarre for someone to use his knee to point at a container, this oddness disappears once we see that the person has his hands full.
Relevant references:
Buttelmann, D., Carpenter, M., McCall, J., & Tomasello, M. (2007). Enculturated chimpanzees imitate rationality. Developmental Science 10(4), F31-F38.
Range, F., Viranyi, Z., & Huber, L. (2007). Selective imitation in domestic dogs. Current Biology, 17, 1-5.
Rizzolatti, G., Fadiga, L., Fogassi, L., & Gallese, V. (1999). Resonance behaviors and mirror neurons. Archives Italiennes de Biologie, 137.
Wood, J.N., Glynn, D.D., & Hauser, M.D. (2008). Rhesus monkeys' understanding of actions and goals. Social Neuroscience, 3, 60-68.
Wood, J.N., Glynn, D.D., & Hauser, M.D. (2007). The uniquely human capacity to throw evolved from a non-throwing primate: an evolutionary dissociation between action and perception. Biology Letters, 3, 360-364.
Wood, J.N., Glynn, D.D., Phillips, B.C., & Hauser, M.D. (2007). The perception of rational, goal-directed human action in nonhuman primates. Science, 317, 1402-1405.