Group decisions in humans and animals: a survey

Abstract

Humans routinely make many decisions collectively, whether they choose a restaurant with friends, elect political leaders or decide actions to tackle international problems, such as climate change, that affect the future of the whole planet. We might be less aware of it, but group decisions are just as important to social animals as they are for us. Animal groups have to collectively decide about communal movements, activities, nesting sites and enterprises, such as cooperative breeding or hunting, that crucially affect their survival and reproduction. While human group decisions have been studied for millennia, the study of animal group decisions is relatively young, but is now expanding rapidly. It emerges that group decisions in animals pose many similar questions to those in humans. The purpose of the present issue is to integrate and combine approaches in the social and natural sciences in an area in which theoretical challenges and research questions are often similar, and to introduce each discipline to the other's key ideas, findings and successful methods. In order to make such an introduction as effective as possible, here, we briefly review conceptual similarities and differences between the sciences, and provide a guide to the present issue.Keywords: collective decisions; communal decisions; conflict resolution; cooperation; information sharing; social behaviour GENERAL BACKGROUNDHumans usually live in highly sophisticated societies. This implies that many important decisions are made not by individuals acting alone, but by groups of individuals acting collectively. Group decisions in humans range from small-scale decisions, such as those taken by groups of relatives, friends or colleagues, to large-scale decisions, such as nation-wide democratic elections and international agreements. Clearly, human societies cannot function without group decisions, and some of the most pressing problems facing humanity result from failures to reach a group consensus (e.g. the signing of the Kyoto treaty on controlling greenhouse gas emissions). Group decision making has been a central topic in all of the social sciences for millennia (e.g. Plato: The Republic 360 BC). Nevertheless, many questions remain open, particularly how conflicting interests and the sharing of dispersed information are actually, and should be, in principle, reconciled so as to facilitate cooperation and to reach outcomes that meet various optimality criteria. These are some of the fundamental questions of social choice theory (e.g. Arrow 1951Arrow /1963Austen-Smith & Banks 1999Sen 1999;Dryzek & List 2003). A large number of animal species also live in groups (Krause & Ruxton 2002), some of which can be very complex (e.g. eusocial bees, wasps, ants, termites and mole rats). Group decision making is just as important for social animals as it is for us (see Conradt & Roper 2005 for a review). Dispersing swarms of bees and ants collectively choose new nest sites on which their survival depends (Seeley & Buhrman 1999;Visscher 2007;Visscher & Seele...

Decision accuracy in complex environments is often maximized by small group sizes

“…Each individual's voting strategy is to choose the low correlation cue with probability p and the high correlation cue with probability 1 2 p and to vote for the option indicated by that cue. Majority consensus determines the collective decision [15,18,38,39].…”

“…Collective intelligence also has wide applicability in human decision-making, including law-making bodies, prediction markets and corporations. While there is growing evidence that the wisdom of crowds leads to substantially improved decision accuracy [16][17][18][19][20]62], it is still not well understood how it operates in complex, real-world conditions. For example, how social information is shared between group members can affect the resulting decision accuracy [40] and can often undermine the wisdom of crowds by improving confidence in the collective decision without improving its accuracy [63].…”

“…A further reduction of uncertainty may be achieved by incorporating social cues into the decision-making process [4,[6][7][8][9][10][11][12][13][14][15]. It has been suggested that by pooling imperfect estimations, groups may achieve increased decision accuracy, the so-called wisdom of crowds [16][17][18][19][20][21].…”

“…Theoretical and empirical work has shown that the social interaction rules adopted by many organisms effectively integrate the opinions of the group, such that the resulting collective decision often closely mirrors the majority opinion [15,18,[22][23][24]38,39]. Consequently, although they may lack the capacity for numerosity (the ability to explicitly count or tally), or to explicitly cast a 'vote', organisms such as schooling fish do effectively perform majority consensus decision-making through their employment of simple and local social interactions [15,[22][23][24]39].…”

How institutions shaped the last major evolutionary transition to large-scale human societies

“…Thus, although each individual should be expected to try to craft institutional rules that benefit itself, the egalitarian social structure would have prevented any one individual from being able to benefit itself too much at the expense of the rest of the group. Consequently, the political game form was likely to take the shape of a mechanism that aggregated the preferences of all group members [58] without resulting in too much dissent.…”