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Collective cognition in animal groups

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The remarkable collective action of organisms such as swarming ants, schooling fish and flocking birds has long captivated the attention of artists, naturalists, philosophers and scientists. Despite a long history of scientific investigation, only now are we beginning to decipher the relationship between individuals and group-level properties. This interdisciplinary effort is beginning to reveal the underlying principles of collective decision-making in animal groups, demonstrating how social interactions, individual state, environmental modification and processes of informational amplification and decay can all play a part in tuning adaptive response. It is proposed that important commonalities exist with the understanding of neuronal processes and that much could be learned by considering collective animal behavior in the framework of cognitive science.

Introduction

It is little wonder that the behavior of animal groups, such as schools of fish, flocks of birds or swarms of insects has been associated with the concept of having a ‘collective mind’ [1]. Grouping individuals often have to make rapid decisions about where to move or what behavior to perform, in uncertain and dangerous environments. Decision-making by individuals within such aggregates is so synchronized and intimately coordinated that it has previously been considered to require telepathic communication among group members or the synchronized response to commands given, somehow, by a leader 2, 3.

In fact, individuals base their movement decisions on locally acquired cues such as the positions, motion, or change in motion, of others [2], making the collective response all the more remarkable. Each organism typically has only relatively local sensing ability (further limited in large aggregates by crowding). Groups are, therefore, often composed of individuals that differ with respect to their informational status and individuals are usually not aware of the informational state of others, such as whether they are knowledgeable about a pertinent resource, or of a threat 1, 2, 4, 5.

Recent studies have begun to elucidate how the repeated interactions among grouping animals scale to collective behavior, and have revealed, remarkably, that collective decision-making mechanisms across a wide range of animal group types, from insects to birds (and even among humans in certain circumstances) seem to share similar functional characteristics 2, 4, 5. Furthermore, at a certain level of description, collective decision-making by organisms shares essential common features with mechanisms of decision-making within the brain 1, 6. Although many details differ, there is good reason for increased communication between researchers interested in collective animal behavior and those in cognitive science.

Section snippets

Collective motion

It is usually not possible to scale reliably from individual to group behavior through verbal argument alone. Consequently, considerable progress in revealing the principles of collective behavior has been made using mathematical modeling techniques, such as computer simulation (Box 1). Some of the earliest theoretical approaches were inspired by particle physics 2, 7. These introduced the influential concept of using equations to characterize individual movements and interactions (as ‘social

Feedback processes

The social context created by highly integrated behavior strongly affects the way information is acquired, transmitted and processed by group members. Specifically, it can facilitate the collective amplification and damping of information and, thus, the adaptive tuning of collective behavior in response to external stimuli and/or internal state.

Alignment among individuals (a tendency to move in the same direction as near-neighbors, Box 1), for example, can enable information about a change in

Group size and collective decision-making

Group size can also have an important role in decision-making. If individuals have access to the same information, but it is inaccurately represented or processed, then averaging response with others (as is inherent in many schooling or flocking strategies; Box 1), will improve the decisions of the group-members. This can enable individuals to avoid the time costs associated with temporal integration and has sometimes been referred to as ‘the many-wrongs hypothesis’ [29] or ‘the wisdom of the

Leadership and coming to a consensus decision

Although leadership is not a pre-condition for group coordination it does frequently emerge in animal groups 2, 4, 31 such as when only relatively few ‘informed’ individuals have salient information [31]. Using computational modeling, Couzin et al. [31] revealed that information transfer within groups requires neither individual recognition nor signaling. If relatively few informed individuals bias grouping tendency with a desired direction of travel (such as towards a resource or away from a

Collective cognition through environmental modification: foraging ants

In highly related grouping organisms, such as the social insects (e.g. ants, bees, wasps etc.), collective cognition can be particularly sophisticated because individual behavior and interactions have evolved to benefit the colony reproductive success (thus reducing inter-individual conflict), a functional integration so tight that they have been termed ‘super-organisms’ [36]. This is exemplified by ant species that use chemical pheromone trails to coordinate foraging activities [36].

By

Finding a new home

In addition to selecting among potential food sources, social insects need to choose where to live. This process has been studied extensively in two, apparently very different, organisms; a species of small ant, Temnothorax albipennis, which lives in colonies of between ∼50 to 200 individuals in naturally weathered cracks in rocks (these ants are similar to those shown in Box 2, Figure I), and the honeybee, Apis mellifera, which typically lives in colonies of tens of thousands of individuals

Conclusions and future research

Through collective action, animals of many species can enhance their capacity to detect and respond to salient features of the environment. Interactions with others can enable individuals to circumvent their own cognitive limitations, giving them access to context-dependent and spatially and temporally integrated information. This can result in more accurate decision-making even in the face of distractions and uncertainty. Collective behavior allows access to important higher-order

Acknowledgements

I.D.C. gratefully acknowledges support from a Searle Scholar Award and also a DARPA grant #HR001–05–1-0057 to Princeton University. Insightful suggestions from three anonymous referees much improved the manuscript. Sepideh Bazazi, Adrian De Froment, Vishwesha Guttal, Christos Ioannou, Yael Katz, Liliana Salvador and Allison Shaw provided valuable feedback.

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