Individual and social discounting in a viscous population

Sozou, Peter D.

doi:10.1098/rspb.2009.0401

Cited by 20 publications

(32 citation statements)

References 36 publications

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“…These analyses demonstrate that scaled relatedness will in general decrease with group size (e.g. Aoki, 1982;Taylor, 1992;Taylor & Irwin, 2000;Roze & Rousset, 2004;Gardner & West, 2006;Lehmann, Perrin & Rousset, 2006;Johnstone & Cant, 2008;Sozou, 2009;Gardner, 2010;Ohtsuki, 2010;Van Dyken, 2010;Bao & Wild, 2012;Kuijper & Johnstone, 2012;Rodrigues & Gardner, 2012;Van Dyken & Wade, 2012). It is worth noting here that the size of the breeding group (deme) in island models may not be the same as the size of the social group in which helping interactions occur.…”

Section: (2) Lattice Models and Other Variations Of The Baseline Groumentioning

confidence: 89%

When is bigger better? The effects of group size on the evolution of helping behaviours

Powers

Lehmann

2016

Biological Reviews

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Understanding the evolution of sociality in humans and other species requires understanding how selection on social behaviour varies with group size. However, the effects of group size are frequently obscured in the theoretical literature, which often makes assumptions that are at odds with empirical findings. In particular, mechanisms are suggested as supporting large-scale cooperation when they would in fact rapidly become ineffective with increasing group size. Here we review the literature on the evolution of helping behaviours (cooperation and altruism), and frame it using a simple synthetic model that allows us to delineate how the three main components of the selection pressure on helping must vary with increasing group size. The first component is the marginal benefit of helping to group members, which determines both direct fitness benefits to the actor and indirect fitness benefits to recipients. While this is often assumed to be independent of group size, marginal benefits are in practice likely to be maximal at intermediate group sizes for many types of collective action problems, and will eventually become very small in large groups due to the law of decreasing marginal returns. The second component is the response of social partners on the past play of an actor, which underlies conditional behaviour under repeated social interactions. We argue that under realistic conditions on the transmission of information in a population, this response on past play decreases rapidly with increasing group size so that reciprocity alone (whether direct, indirect, or generalised) cannot sustain cooperation in very large groups. The final component is the relatedness between actor and recipient, which, according to the rules of inheritance, again decreases rapidly with increasing group size. These results explain why helping behaviours in very large social groups are limited to cases where the number of reproducing individuals is small, as in social insects, or where there are social institutions that can promote (possibly through sanctioning) large-scale cooperation, as in human societies. Finally, we discuss how individually devised institutions can foster the transition from small-scale to large-scale cooperative groups in human evolution.

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Section: (2) Lattice Models and Other Variations Of The Baseline Groumentioning

confidence: 89%

When is bigger better? The effects of group size on the evolution of helping behaviours

Powers

Lehmann

2016

Biological Reviews

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“…As discussed in Section 1, the discount rate decreases in childhood. In adulthood, on the other hand, while still empirically inconclusive, Trostel and Taylor [28] and Read and Read [29] found that the discount rate increases with senescence 12 . The present study focuses on the biological discount rate ignoring the effect of social factors such as education, and may overestimate the discount rate in adulthood in modern human populations.…”

Section: Time Preferencementioning

confidence: 99%

“…evolutionary origin of time preference. More recently, technical similarities for studying aging in bio-demography and the intertemporal allocation in economics have allowed biologists, demographers and economists to enter this hybrid field, leading to the examination of how the time-discounting behavior relates to senescence (Sozou and Seymour [9]) and to intergenerational transfers (Chu et al [10]), why it is hyperbolic (Robson and Samuelson [11]), the rationale for social discounting (Sozou [12]), how it depends on age (Kageyama [13]), and how it relates to extrinsic mortality (Chowdhry [14]) 3 . To investigate the impatience of children, the present study follows this literature and extends Kageyama [13] by incorporating childhood, i.e., the growth period to maturity.…”

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confidence: 99%

Why Are Children Impatient? Evolutionary Selection of Preferences

Kageyama¹

2013

TEL

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This study aims to explain why children are impatient. Using a biological framework called the life history theory, the study investigates the evolutionary root of time preference, paying particular attention to childhood. The results show that the biologically endowed rate of time preference is equal to the mortality rate not only in adulthood but also in childhood, reflecting the change in the biological value of survival. Mortality is the baseline for time preference through the entire course of life. These results are consistent with the findings in previous empirical and experimental studies that the discount rate is U-shaped in age, and account for why young children, in particular, are impatient. In addition, the difference in time preference between adults and children provides a biological explanation for the parent-offspring conflict, in which the higher discount rate among children causes parents and their children to disagree over intertemporal allocation of resources in collective decision-making particularly within the household.

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“…Grafen 1984; Taylor 1992; Queller 1994; Taylor & Irwin 2000; West et al. 2007; Grafen & Archetti 2008; Johnstone & Cant 2008; Sozou 2009).…”

Section: Evolutionary Equilibrium Under the Joint Action Of Natural Sunclassified

“…Individuals not only may discount future rewards to self, or to their offspring, but are also likely to discount future rewards to other individuals living in their group or in other groups from the population. Social discounting involves applying a diminishing weight to group‐wide future benefits (Sozou 2009). As most natural populations tend to be spatially structured (Clobert et al.…”

Section: Introductionmentioning

confidence: 99%

The evolution of social discounting in hierarchically clustered populations

Lehmann

Rousset

2011

Molecular Ecology

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The expression of a social behaviour may affect the fitness of actors and recipients living in the present and in the future of the population. When there is a risk that a future reward will not be experienced in such a context, the value of that reward should be discounted; but by how much? Here, we evaluate social discount rates for delayed fitness rewards to group of recipients living at different positions in both space and time than the actor in a hierarchically clustered population. This is a population where individuals are grouped into families, families into villages, villages into clans, and so on, possibly ad infinitum. The group-wide fitness effects are assumed to either increase or decrease the fecundity or the survival of recipients and can be arbitrarily extended in space and time. We find that actions changing the survival of individuals living in the future are generally more strongly discounted than fecundity-changing actions for all future times and that the value of future rewards increases as individuals live longer. We also find that delayed fitness effects may not only be discounted by a constant factor per unit delay (exponential discounting), but that, as soon as there is localized dispersal in a population, discounting per unit delay is likely to fall rapidly for small delays and then slowly for longer delays (hyperbolic discounting). As dispersal tends to be localized in natural populations, our results suggest that evolution is likely to favour individuals that express present-biased behaviours and that may be time-inconsistent with respect to their groupwide effects.

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Individual and social discounting in a viscous population

Cited by 20 publications

References 36 publications

When is bigger better? The effects of group size on the evolution of helping behaviours

When is bigger better? The effects of group size on the evolution of helping behaviours

Why Are Children Impatient? Evolutionary Selection of Preferences

The evolution of social discounting in hierarchically clustered populations

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