scholarly journals Group and individual selection during evolutionary transitions in individuality: meanings and partitions

2020 ◽  
Vol 375 (1797) ◽  
pp. 20190364 ◽  
Author(s):  
Deborah E. Shelton ◽  
Richard E. Michod
Keyword(s):  
Group Selection ◽  
Contextual Analysis ◽  
Price Equation ◽  
Individual Selection ◽  
Evolutionary Transition ◽  
Theme Issue ◽  
Heritable Variation ◽  
Selection Models ◽  
Evolutionary Transitions ◽  
Multi Level

The Price equation embodies the ‘conditions approach’ to evolution in which the Darwinian conditions of heritable variation in fitness are represented in equation form. The equation can be applied recursively, leading to a partition of selection at the group and individual levels. After reviewing the well-known issues with the Price partition, as well as issues with a partition based on contextual analysis, we summarize a partition of group and individual selection based on counterfactual fitness, the fitness that grouped cells would have were they solitary. To understand ‘group selection’ in multi-level selection models, we assume that only group selection can make cells suboptimal when they are removed from the group. Our analyses suggest that there are at least three kinds of selection that can be occurring at the same time: group-specific selection along with two kinds of individual selection, within-group selection and global individual selection. Analyses based on counterfactual fitness allow us to specify how close a group is to being a pseudo-group, and this can be a basis for quantifying progression through an evolutionary transition in individuality (ETI). During an ETI, fitnesses at the two levels, group and individual, become decoupled, in the sense that fitness in a group may be quite high, even as counterfactual fitness goes to zero. This article is part of the theme issue ‘Fifty years of the Price equation’.

scholarly journals Identifying Causes of Social Evolution: Contextual Analysis, the Price Approach, and Multilevel Selection

2021 ◽  
Vol 9 ◽  
Author(s):  
Christoph Thies ◽  
Richard A. Watson
Keyword(s):  
Kin Selection ◽  
Causal Structure ◽  
Multilevel Selection ◽  
Contextual Analysis ◽  
Price Equation ◽  
Evolutionary Transitions ◽  
Selection Theory ◽  
Individual Fitness ◽  
Multilevel Selection Theory ◽  
The Individual

Kin selection theory and multilevel selection theory are distinct approaches to explaining the evolution of social traits. The latter claims that it is useful to regard selection as a process that can occur on multiple levels of organisation such as the level of individuals and the level of groups. This is reflected in a decomposition of fitness into an individual component and a group component. This multilevel view is central to understanding and characterising evolutionary transitions in individuality, e.g., from unicellular life to multicellular organisms, but currently suffers from the lack of a consistent, quantifiable measure. Specifically, the two major statistical tools to determine the coefficients of such a decomposition, the multilevel Price equation and contextual analysis, are inconsistent and may disagree on whether group selection is present. Here we show that the reason for the discrepancies is that underlying the multilevel Price equation and contextual analysis are two non-equivalent causal models for the generation of individual fitness effects (thus leaving different “remainders” explained by group effects). While the multilevel Price equation assumes that the individual effect of a trait determines an individual's relative success within a group, contextual analysis posits that the individual effect is context-independent. Since these different assumptions reflect claims about the causal structure of the system, the correct approach cannot be determined on general theoretical or statistical grounds but must be identified by experimental intervention. We outline interventions that reveal the underlying causal structure and thus facilitate choosing the appropriate approach. We note that kin selection theory with its focus on the individual is immune to such inconsistency because it does not address causal structure with respect to levels of organisation. In contrast, our analysis of the two approaches to measuring group selection demonstrates that multilevel selection theory adds meaningful (falsifiable) causal structure to explain the sources of individual fitness and thereby constitutes a proper refinement of kin selection theory. Taking such refined causal structure into account seems indispensable for studying evolutionary transitions in individuality because these transitions are characterised by changes in the selection pressures that act on the respective levels.

scholarly journals The Price equation as a bridge between animal breeding and evolutionary biology

2020 ◽  
Vol 375 (1797) ◽  
pp. 20190360 ◽  
Author(s):  
P. Bijma
Keyword(s):  
Evolutionary Biology ◽  
Genetic Effect ◽  
Price Equation ◽  
Response To Selection ◽  
Theme Issue ◽  
Heritable Variation ◽  
Indirect Genetic Effect ◽  
Trait Distribution ◽  
The Social ◽  
Genetic Standard Deviation

The genetic response to selection is central to both evolutionary biology and animal and plant breeding. While Price's theorem (PT) is well-known in evolutionary biology, most breeders are unaware of it. Rather than using PT, breeders express response to selection as the product of the intensity of selection ( i ), the accuracy of selection ( ρ ) and the additive genetic standard deviation ( σ A ); R = iρσ A . In contrast to the univariate ‘breeder's equation’, this expression holds for multivariate selection on Gaussian traits. Here, I relate R = iρσ A to PT, and present a generalized version, R = i w ρ A , w σ A , valid irrespective of the trait distribution. Next, I consider genotype–environment covariance in relation to the breeder's equation and PT, showing that the breeder's equation may remain valid depending on whether the genotype–environment covariance works across generations. Finally, I consider the response to selection in the prevalence of an endemic infectious disease, as an example of an emergent trait. The result shows that disease prevalence has much greater heritable variation than currently believed. The example also illustrates that the indirect genetic effect approach moves elements of response to selection from the second to the first term of PT, so that changes acting via the social environment come within the reach of quantitative genetics. This article is part of the theme issue ‘Fifty years of the Price equation’.

scholarly journals The problem with the Price equation

2020 ◽  
Vol 375 (1797) ◽  
pp. 20190355 ◽  
Author(s):  
Matthijs van Veelen
Keyword(s):  
Group Selection ◽  
Social Evolution ◽  
Linear Models ◽  
Fitness Function ◽  
Regression Coefficients ◽  
Price Equation ◽  
Theme Issue

In this paper, I will argue that the generality of the Price equation comes at a cost, and that is that the terms in it become meaningless. There are simple linear models that can be written in a Price equation-like form, and for those the terms in them have a meaningful interpretation. There are also models for which that is not the case, and in general, when no assumptions on the shape of the fitness function are made, and all possible models are allowed for, the regression coefficients in the Price equation do not allow for a meaningful interpretation. The failure to recognize that the Price equation, although general, only has a meaningful interpretation under restrictive assumptions, has done real damage to the field of social evolution, as will be illustrated by looking at an application of the Price equation to group selection. This article is part of the theme issue ‘Fifty years of the Price equation’.

scholarly journals The Price equation and the unity of social evolution theory

2020 ◽  
Vol 375 (1797) ◽  
pp. 20190362 ◽  
Author(s):  
Jussi Lehtonen
Keyword(s):  
Group Selection ◽  
Social Evolution ◽  
Causal Structure ◽  
Mathematical Structure ◽  
Price Equation ◽  
Alternative Formulation ◽  
Evolution Theory ◽  
Weak Selection ◽  
Theme Issue ◽  
Modelling Methods

The Price equation has been entangled with social evolution theory from the start. It has been used to derive the most general versions of kin selection theory, and Price himself produced a multilevel equation that provides an alternative formulation of social evolution theory, dividing selection into components between and within groups. In this sense, the Price equation forms a basis for both kin and group selection, so often pitted against each other in the literature. Contextual analysis and the neighbour approach are prominent alternatives for analysing group selection. I discuss these four approaches to social evolution theory and their connections to the Price equation, focusing on their similarities and common mathematical structure. Despite different notations and modelling traditions, all four approaches are ultimately linked by a common set of mathematical components, revealing their underlying unity in a transparent way. The Price equation can similarly be used in the derivation of streamlined, weak selection social evolution modelling methods. These weak selection models are practical and powerful methods for constructing models in evolutionary and behavioural ecology; they can clarify the causal structure of models, and can be easily converted between the four social evolution approaches just like their regression counterparts. This article is part of the theme issue ‘Fifty years of the Price equation’.

scholarly journals Identifying causes of social evolution: The Price approach, contextual analysis, and multilevel selection

2020 ◽  
Author(s):  
Christoph Thies ◽  
Richard A. Watson
Keyword(s):  
Kin Selection ◽  
Group Selection ◽  
Causal Structure ◽  
Multilevel Selection ◽  
Contextual Analysis ◽  
Price Equation ◽  
Selection Theory ◽  
Individual Fitness ◽  
Multilevel Selection Theory ◽  
The Individual

AbstractKin selection theory and multilevel selection theory are different approaches to explaining the evolution of social traits. The latter claims that it is useful to regard selection as a process that can occur on multiple levels of organisation such as the level of individuals and the level of groups. This is reflected in a decomposition of fitness into an individual component and a group component. However, the two major statistical tools to determine the coefficients of such a decomposition, the multilevel Price equation and contextual analysis, are inconsistent and may disagree on whether group selection is present. Here we show that the reason for the discrepancies is that underlying the multilevel Price equation and contextual analysis are two nonequivalent causal models for the generation of individual fitness effects (thus leaving different ‘remainders’ explained by group effects). While the multilevel Price equation assumes that the individual effect of a trait determines an individual’s relative success within a group, contextual analysis posits that the individual effect is context-independent. Since these different assumptions reflect claims about the causal structure of the system, the correct approach cannot be determined on general theoretical or statistical grounds but must be identified by experimental intervention. We outline interventions that reveal the underlying causal structure and thus facilitate choosing the appropriate approach. We note that the reductionist viewpoint of kin selection theory with its focus on the individual is immune to such inconsistency because it does not address causal structure with respect to levels of organisation. In contrast, our analysis of the two approaches to measuring group selection demonstrates that multilevel selection theory adds meaningful (falsifiable) causal structure to explain the sources of individual fitness and thereby constitutes a proper refinement of kin selection theory.

scholarly journals Conflict and cooperation in eukaryogenesis: implications for the timing of endosymbiosis and the evolution of sex

2015 ◽  
Author(s):  
Arunas L Radzvilavicius ◽  
Neil W Blackstone
Keyword(s):  
Cell Fusion ◽  
Mitochondrial Gene ◽  
Evolutionary Process ◽  
Eukaryotic Cell ◽  
Evolutionary Transition ◽  
Evolutionary Transitions ◽  
Conflict And Cooperation ◽  
Conflict Mediation ◽  
Considerable Debate ◽  
History Of

The complex eukaryotic cell is a result of an ancient endosymbiosis and one of the major evolutionary transitions. The timing of key eukaryotic innovations relative to the acquisition of mitochondria remains subject to considerable debate, yet the evolutionary process itself might constrain the order of these events. Endosymbiosis entailed levels-of-selection conflicts, and mechanisms of conflict mediation had to evolve for eukaryogenesis to proceed. The initial mechanisms of conflict mediation were based on the pathways inherited from prokaryotic symbionts and led to metabolic homeostasis in the eukaryotic cell, while later mechanisms (e.g., mitochondrial gene transfer) contributed to the expansion of the eukaryotic genome. Perhaps the greatest opportunity for conflict arose with the emergence of sex involving whole-cell fusion. While early evolution of cell fusion may have affected symbiont acquisition, sex together with the competitive symbiont behaviour would have destabilised the emerging higher-level unit. Cytoplasmic mixing, on the other hand, would have been beneficial for selfish endosymbionts, capable of using their own metabolism to manipulate the life history of the host. Given the results of our mathematical modelling, we argue that sex represents a rather late proto- eukaryotic innovation, allowing for the growth of the chimeric nucleus and contributing to the successful completion of the evolutionary transition.

scholarly journals The order of trait emergence in the evolution of cyanobacterial multicellularity

2019 ◽  
Author(s):  
Katrin Hammerschmidt ◽  
Giddy Landan ◽  
Fernando Domingues Kümmel Tria ◽  
Jaime Alcorta ◽  
Tal Dagan
Keyword(s):  
Division Of Labor ◽  
Phenotypic Trait ◽  
Evolutionary Transition ◽  
Evolutionary Transitions ◽  
Differentiated Cells ◽  
Labor Theory ◽  
Significant Events ◽  
Reproductive Life ◽  
History Of ◽  
Multicellular Organisms

AbstractThe transition from unicellular to multicellular organisms is one of the most significant events in the history of life. Key to this process is the emergence of Darwinian individuality at the higher level: groups must become single entities capable of reproduction for selection to shape their evolution. Evolutionary transitions in individuality are characterized by cooperation between the lower level entities and by division of labor. Theory suggests that division of labor may drive the transition to multicellularity by eliminating the trade-off between two incompatible processes that cannot be performed simultaneously in one cell. Here we examine the evolution of the most ancient multicellular transition known today, that of cyanobacteria, where we reconstruct the sequence of ecological and phenotypic trait evolution. Our results show that the prime driver of multicellularity in cyanobacteria was the expansion in metabolic capacity offered by nitrogen fixation, which was accompanied by the emergence of the filamentous morphology and succeeded by a reproductive life cycle. This was followed by the progression of multicellularity into higher complexity in the form of differentiated cells and patterned multicellularity.Significance StatementThe emergence of multicellularity is a major evolutionary transition. The oldest transition, that of cyanobacteria, happened more than 3 to 3.5 billion years ago. We find N2 fixation to be the prime driver of multicellularity in cyanobacteria. This innovation faced the challenge of incompatible metabolic processes since the N2 fixing enzyme (nitrogenase) is sensitive to oxygen, which is abundantly found in cyanobacteria cells performing photosynthesis. At the same time, N2-fixation conferred an adaptive benefit to the filamentous morphology as cells could divide their labour into performing either N2-fixation or photosynthesis. This was followed by the culmination of complex multicellularity in the form of differentiated cells and patterned multicellularity.

Group selection models with population substructure based on social interaction networks

1988 ◽  
Vol 77 (4) ◽  
pp. 427-433 ◽  
Author(s):  
James M. Cheverud ◽  
B. Diane Chepko-Sade ◽  
Malcolm M. Dow ◽  
Donald S. Sade
Keyword(s):  
Social Interaction ◽  
Group Selection ◽  
Interaction Networks ◽  
Population Substructure ◽  
Selection Models

Cooperation in a Larger World

2021 ◽  
pp. 93-123
Author(s):  
Kim Sterelny
Keyword(s):  
Social Life ◽  
Group Selection ◽  
Spatial Scales ◽  
Social World ◽  
Intergroup Conflict ◽  
Great Ape ◽  
Residential Group ◽  
Positive Account ◽  
Multi Level ◽  
Human Social Life

This chapter has three aims. First: it presents a positive account of the origins of multi-level society in human social life, for even the simplest forager bands are nested units in larger communities, and those bands are open, with quite free movement in and out, and with individuals having social allies in other bands. This makes possible cooperation in various guises at larger social and spatial scales. Great ape bands, and hence very likely early hominin bands, were closed, with an individual’s residential group being his/her whole social world. Second, it introduces the reader to group selection models of the evolution of human cooperation. Third, it argues against the view that human social life in the Pleistocene was structured by regular intergroup conflict and by its permanent threat.

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