How Nature can Help in Decision Making

Strategies from social animals for consensus decision making

In my previous blogpost “Who’s the boss?” I introduced the challenge around decision making when developing a starfish-like organization structure.

Though a Google Scholar search a found a handful of great articles discussing how social organisms make decisions. Today I’ll discuss the paper Consensus decision making in animals by Conradt & Roper.

The focus of this paper is on consensus decision-making and places different strategies of social animals into a coherent framework. This framework is based on the degree of communication (global vs. local) and conflict of interest.

An important aspect of consensus decisions is that all members abide by the decision outcome, not that all contribute to it. There are three theoretical possibilities concerning the identity of the decision makers:

i) All group members (equally shared decision): consensus is usually reached via a quorum (i.e. a majority, sub-majority or super-majority of members) or by averaging over all the ‘votes’

Examples: Agreements about travel routes in navigating birds [changing mechanism depending on experience of birds]; activity timing and travel destinations in small groups of birds, fish and mammals

ii) Particular subsets of group members (partially shared decision)

Examples: Agreements about travel routes in navigating birds [changing mechanism depending on experience of birds]; Nest choice in honey bees;

iii) The dominant animal (unshared decision): Coercion by a dominant individual is unlikely to work in practice because of the inability of a dominant animal to force a consensus decision, either because it is physically unable to do so, particularly in large groups, or because it would not gain sufficiently to outweigh the costs of coercion.

For example, if a group of animals has to decide between two alternatives, of which one is better for the whole group, and each member has a probability of 0.75 of correctly identifying the better alternative, an unshared decision made by one dominant individual would be wrong with a probability of 0.25. However, if an equally shared consensus decision is made, with a simple majority constituting a quorum, the probability of choosing the ‘wrong’ alternative is 0.16 for a group with three members, 0.10 with five members, 0.07 with seven members, and so on.

A first discriminator for consensus decision-making is the degree of conflict of interest between all member, as this determines the exchange of decision-related information between group members, the degree of cooperation during decision making and the fitness consequences of the decision outcome to individual members. The lower the conflict of interest, the easier to obtain an equally shared decision. To minimize conflict, the goal (e.g. finding the best nest site, or taking the fastest travel route) should be similar for all group members. When conflict becomes too large, this can result in segregation of the group: e.g. conflicts between the sexes about activity budgeting in red deer groups are so large that they lead to intersexual social segregation.

A second discriminator is the degree of communication. Direct (“global”) communication is crucial to allow complex ‘negotiating’ behaviours and coalitions. If global communication is not possible, social organisms use self-organizing rules. These are behavioural rules that individuals can follow using only local information, and which result in an organized group behaviour without the need for global control.

The possibility of information sharing, leading to a more accurate decision outcome, can result in fitness advantages to consensus decision makers. However, the speed with which a consensus decision should be made depend on the number of group members and the number of decision makers. Groups might have to adjust the number of decision makers so as to optimize a tradeoff between speed and accuracy.

I found this framework very helpful in categorizing different decision-making scenarios. Next blog post will cover one or two in-depth examples of social organisms, but in the meantime, if you’d like to read more on this topic, here are some of my favorite readings:

• Norton, G.W. (1986) Leadership decision processes of group movement in yellow baboons. In Primate Ecology and Conservation (Else, J.G. and Lee, P.C., eds), pp. 145–156, Cambridge University Press
• List, C. (2004) Democracy in animal groups: a political science perspective. Trends Ecol. Evol. 19, 168–169
• Couzin, I.D. and Krause, J. (2003) Self-organization and collective behavior in vertebrates. Adv. Stud. Behav. 32, 1–75
• Franks, N. R. et al. (2003) Strategies for choosing between alternatives with different attributes: exemplified by house-hunting ants. Anim. Behav. 65, 215–223
• Franks, N.R. et al. (2002) Information flow, opinion polling and collective intelligence in house-hunting social insects. Philos. Trans. R. Soc. Lond. B Biol. Sc. 357, 1567–1583
• Franks, N.R. et al. (2003) Speed versus accuracy in collective decision- making. Proc. R. Soc. Lond. B Biol. Sci. 270, 2457–2463
• Leca, J.B. et al. (2003) Distributed leadership in semifree-ranging white-faced capuchin monkeys. Anim. Behav. 66, 1045–1052

Thanks for those who already contacted me, but I’d like to hear from more startups who think decision-making is a (daily) challenge.

Let’s connect!