Social selection

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Social selection is a mode of natural selection arising from competitive and cooperative interactions among conspecifics, where traits that confer advantages in social contexts—such as gaining preferred partners for reproduction, parenting, resource access, or alliances—are favored, thereby influencing an individual's reproductive success.^[1] This process encompasses a broad range of social behaviors beyond mere survival or mating, including sibling rivalry, parental favoritism, and coalition formation, making it a unifying framework for understanding the evolution of social traits across species.^[2] The term "social selection" was first introduced by V.C. Wynne-Edwards in 1962 to describe selective forces arising from social hierarchies among group members.^[3] The concept was further formalized by evolutionary biologist Mary Jane West-Eberhard in her 1979 paper, where she extended Darwin's ideas on selection to all forms of intraspecific social competition rather than limiting it to sexual contexts.^[1] West-Eberhard argued that many exaggerated traits, such as ornaments and weapons, evolve through social selection for non-mating purposes, like securing territory or group membership, and she positioned sexual selection—Darwin's mechanism for traits favored through mate choice and competition—as merely a subset of this broader process.^[2] Subsequent work by researchers like Joan Roughgarden has further developed social selection as an alternative paradigm, emphasizing cooperative negotiations in courtship and parental roles over adversarial competition, reversing the logic of sexual selection by starting from offspring production and tracing back to social partnerships.^[4] In practice, social selection has been applied to explain diverse evolutionary phenomena, from the elaborate displays in birds and insects that signal coalition potential rather than just attractiveness, to the evolution of prosocial behaviors in primates where individuals are chosen as allies based on reliability and generosity.^[4] For instance, in species like the Laysan albatross, mutual displays during pair formation function as negotiations for equitable parental investment, highlighting how social selection promotes mutual benefits in long-term relationships.^[4] In human evolution, models of runaway social selection, proposed by Richard D. Alexander in 1990, suggest that intensifying social interactions among early hominins created feedback loops that selected for advanced cognition, language, and cultural norms, transforming humans into their own primary selective agents through eusocial-like dynamics.^[5] Overall, social selection provides a comprehensive lens for integrating social dynamics into evolutionary theory, challenging narrower views by demonstrating how preferences in everyday social interactions can drive rapid and extreme trait evolution, with implications for understanding cooperation, inequality, and cultural diversity across taxa.^[6]

Introduction

Concept Overview

Social selection is an evolutionary process whereby social behaviors and interactions influence individuals' reproductive success, encompassing both cooperative alliances and competitive dynamics that extend beyond mate acquisition to include offspring production and rearing. Unlike natural selection, which focuses on survival advantages, social selection emphasizes how traits evolve through social transactions that enhance fitness via direct ecological benefits, such as resource sharing or protection, rather than solely genetic inheritance from mating. This framework posits that social infrastructure—networks of cooperation and negotiation—underpins reproduction, allowing for diverse social roles and partnerships that optimize group-level outcomes.^[7] In contrast to sexual selection, which originates from Charles Darwin's theory and centers on competition for mates leading to traits like sexual dimorphism, social selection reverses this logic by beginning with offspring viability and tracing backward to the social coalitions that support it. Sexual selection often predicts exaggerated male traits due to intrasexual rivalry and intersexual choice, but social selection highlights scenarios where such competition is minimal, and inclusive social bonds predominate, explaining phenomena without invoking mate-focused rivalry. This distinction underscores social selection's broader scope, integrating competitive and cooperative elements within social contexts to drive evolutionary change. The concept, first formalized by Mary Jane West-Eberhard in 1979 as a broad mode of natural selection including sexual selection as a subset, was further developed by Joan Roughgarden in the early 2000s as a direct alternative to sexual selection, emphasizing cooperation over competition.^[1] A core principle of social selection, as articulated by Joan Roughgarden, involves a two-tiered evolutionary process: behavioral evolution occurs first through dynamic social interactions and transactions, followed by genetic adaptations that stabilize successful strategies. This approach draws on game theory to model how behaviors like alliance formation yield direct benefits, evolving into heritable traits over time. In monomorphic species, such as many bird species (e.g., numerous passerines), where males and females exhibit similar appearances, social selection accounts for elaborate traits like plumage or songs as signals of cooperative reliability rather than mating prowess, absent the dimorphism expected under sexual selection.^[7] The concept gained prominence through Roughgarden's 2004 book Evolution's Rainbow and 2009 book The Genial Gene, challenging traditional views by prioritizing social inclusion over competition. Social selection also relates briefly to anisogamy, the evolutionary divergence in gamete size, by framing it within cooperative social dynamics rather than competitive origins.

Historical Development

The concept of social selection traces its early roots to the work of entomologist Mary Jane West-Eberhard, who in 1979 highlighted social competition as a driver of evolutionary change in insect societies, distinguishing it from mate-focused sexual selection by emphasizing contests over resources like food and nesting sites. West-Eberhard expanded this framework in 1983, proposing that social selection fosters rapid phenotypic divergence and speciation through non-mating interactions, particularly in social insects where cooperative and competitive behaviors shape trait evolution.^[8] Building on these foundations, evolutionary biologist Joan Roughgarden formalized social selection as a direct alternative to sexual selection in the mid-2000s, critiquing Darwinian emphasis on intrasexual rivalry and intersexual choice. In her 2004 book Evolution's Rainbow, Roughgarden argued that diverse reproductive strategies, including cooperation and same-sex behaviors, better explain variation in nature than traditional sexual selection narratives. She advanced this in key papers from 2004 to 2006, culminating in a provocative 2006 Science review co-authored with Meeko Oishi and Erol Akçay, which reframed reproduction as a cooperative social process governed by partner choice for mutual benefits rather than adversarial mating competitions.^[9] Roughgarden synthesized these ideas in her 2009 book The Genial Gene, positing social selection as a paradigm shift toward viewing evolution through the lens of transactional alliances and prosocial traits. The 2006 Science paper ignited immediate controversy within the evolutionary biology community, prompting ten critical letters from leading researchers, including Tim Clutton-Brock, Marlene Zuk, and Richard Prum, who charged the authors with oversimplifying sexual selection's empirical support, ignoring mate choice evidence, and failing to provide a viable replacement mechanism. These responses, published in the same journal, underscored tensions between established sexual selection orthodoxy and emerging social frameworks but also amplified discourse on reproductive evolution. Post-2006, Roughgarden mounted defenses and refinements, notably in a 2012 Philosophical Transactions of the Royal Society B paper that reconciled social selection with indirect fitness theory via game-theoretic equations modeling inclusive fitness gains from social partnerships. This integration addressed critics by linking social selection to kin selection principles without relying on sexual conflict. Recent expansions have applied the concept to human evolution, as in a 2022 Frontiers in Ecology and Evolution article by Bernard Crespi and Mark Flinn, which elaborates Richard Alexander's 1990 model of runaway social selection, where escalating within-group competitions for status and alliances drove cognitive and behavioral traits in hominins.^[5]

Theoretical Foundations

Genetic Principles

Social selection contributes to the maintenance of genetic diversity by favoring cooperative alliances among individuals, which allow for the persistence of varied genotypes through mutual benefits rather than through zero-sum parasitic competitions that might erode variability. In this framework, social interactions enable the formation of reproductive teams or coalitions that distribute reproductive efforts, thereby buffering against environmental fluctuations and preserving a broader genetic portfolio across populations. This contrasts with competitive dynamics, where arms races could lead to fixation of singular advantageous traits, reducing overall diversity. The evolution of anisogamy under social selection arises from social competition among hermaphroditic individuals, where indirect reciprocity promotes differentiation in gamete sizes to optimize fertilization success through cooperative contact rather than gametic conflict. Starting from a hermaphroditic baseline—prevalent in most species, particularly basal lineages like marine invertebrates and early plants—social selection drives the separation into distinct sexes only when specific conditions, such as resource scarcity, necessitate specialized roles to enhance reproductive efficiency and alliance stability.^[10] For instance, in resource-limited environments, dividing gamete production allows for reciprocal investments that sustain population viability without the inefficiencies of universal hermaphroditism. Social selection integrates with indirect fitness concepts by adapting Hamilton's rule, rB > C, where r is genetic relatedness, B the benefit to recipients, and C the cost to the actor, to account for social benefits in multi-individual interactions beyond strict kin. Extensions incorporate feedback from mutualistic partnerships (kith selection) or synergistic trait matching (kind selection), yielding conditions like \beta_{WP.P'} + \beta_{WP'.P} \beta_{P'P} > 0 for neighbor-modulated fitness effects, where \beta terms represent partial regression coefficients for social influences on fitness and phenotypes. This adaptation highlights how cooperative social structures amplify indirect fitness gains in diverse groups.

Behavioral Principles

Social selection operates through behavioral mechanisms where individuals engage in social transactions, exchanging aid such as grooming or territory defense to secure reproductive opportunities and form alliances that enhance survival and fitness. These interactions prioritize cooperative exchanges over solitary efforts, allowing groups to optimize resource allocation and parental care. For instance, in cooperative breeding systems, individuals trade assistance in offspring rearing for access to mating within the group.^[11] The process follows a two-tiered evolutionary framework, in which behaviors evolve rapidly through learning, cultural transmission, and individual plasticity before exerting selective pressure on underlying genes. This initial behavioral tier enables quick adaptations to social environments, such as forming temporary coalitions for mutual benefit, which then reinforce genetic predispositions over generations. Genetic reinforcement of these behaviors occurs subsequently, stabilizing traits that support ongoing social dynamics. In social selection, traits evolve amid a balance of competition and cooperation, where displays and ornaments signal reliability for coalition partnerships rather than solely for mate attraction. Social competition arises in contests for alliance positions, but cooperation predominates as individuals prefer partners who contribute to group stability, such as through shared vigilance or foraging. This shifts emphasis from intrasexual rivalry to inter-individual negotiations that foster prosocial traits advantageous in group settings.^[11] Behaviors in social selection emerge from matrices of social states, representing the intersection of genetic predispositions with varying social environments, such as dominance hierarchies where rank influences access to resources and mates. In these matrices, an individual's actions—aggressive or affiliative—depend on its genetic baseline and the prevailing social context, leading to emergent patterns like hierarchical stability or fluid alliances. For example, in dominance structures, subordinate individuals may employ submissive signals to avoid conflict and gain indirect reproductive benefits through group tolerance. A representative example is observed in bonobos (Pan paniscus), where same-sex pairings, including homosexual interactions, serve as social bonding mechanisms to reduce tension and secure access to group resources and mating opportunities. These behaviors strengthen female coalitions, enhancing collective defense and foraging success, thereby illustrating how non-reproductive social exchanges underpin evolutionary fitness.

Key Models

Portfolio Hypothesis

The portfolio hypothesis, proposed by Joan Roughgarden, posits that sexual reproduction persists because it generates a diverse "portfolio" of genetic combinations among offspring, thereby buffering populations against unpredictable environmental variability, in contrast to asexual reproduction which produces genetically identical clones vulnerable to uniform threats. Under social selection, this diversity arises from cooperative mating interactions that promote recombination, ensuring that not all offspring share the same vulnerabilities and increasing overall reproductive success in fluctuating conditions. The mathematical foundation of the hypothesis relies on probability models demonstrating that genetic diversity reduces variance in fitness outcomes. For instance, the variance in fitness across a portfolio of genotypes can be expressed as \text{Var}(F) = \sum p_i (1 - p_i), where p_i represents the frequency of the i-th allele; this formulation highlights how heterozygosity and recombination lower the risk of total reproductive failure compared to clonal uniformity. Unlike the Red Queen hypothesis, which emphasizes an endless arms race against parasites driving sexual reproduction, the portfolio hypothesis under social selection prioritizes cooperative gene mixing for stability rather than perpetual conflict and parasitism. An illustrative example is a population of dandelions employing mixed mating strategies, where sexual reproduction yields a varied array of seeds resilient to diverse environmental stresses, such as varying soil conditions or herbivore pressures, outperforming purely asexual clones in heterogeneous habitats. Empirical support comes from studies on plants showing that social cues, like pollen competition and neighbor density, influence mixed mating systems to maintain genetic diversity and enhance population resilience. Similarly, in invertebrates such as social insects, genetic diversity modulated by social recognition cues during mating promotes cooperative colony structures and reduces inbreeding depression, aligning with portfolio benefits. Roughgarden elaborated on this hypothesis in her 2009 book The Genial Gene: Deconstructing Darwinian Selfishness, integrating it into a broader framework of social selection.

IR Model of Anisogamy

The IR model of anisogamy, developed by Priya Iyer and Joan Roughgarden, is a population genetic framework that simulates the transition from hermaphroditic isogamy to gamete dimorphism through ecological mechanisms within the context of social selection. In this model, hermaphroditic individuals initially produce equal-sized gametes but evolve specialization—producing either numerous small gametes (proto-sperm) or fewer large gametes (proto-eggs)—as adaptations that increase gamete encounter rates and enhance zygote fitness, particularly in environments with high zygote mortality or low growth rates, such as external fertilization.^[12] The model assumes starting conditions of isogamy with equal gamete investment at a single locus coding for both sperm and egg sizes, without relying on gametic conflict. A key aspect is the use of a Vance survival function to model zygote fitness based on size, where fitness increases with larger zygotes to promote encounter rates and survival; anisogamy emerges via fixation of a single allele under disruptive selection favoring dimorphism for mobility (small gametes) and viability (large gametes). Under these dynamics, the model derives that a 1:1 sex ratio (or gamete production ratio) evolves only if ecological conditions balance strategies equally; otherwise, disruptive selection drives dimorphism.^[12] Published in 2008, the model has been validated against empirical patterns in Volvocales (green algae), where anisogamy aligns with high zygote mortality and isogamy with lower mortality/higher growth, consistent with predictions for enhanced fertilization success.^[12] Social state matrices serve as a key analytical tool in social selection theory, providing a structured framework to predict individual behaviors and group outcomes by mapping the interplay between genetic predispositions and prevailing social conditions. These matrices are constructed as two-dimensional grids, with rows typically representing distinct genetic states—such as high or low expression of genes associated with traits like aggression or cooperation—and columns denoting variations in social states, including factors like group size, resource distribution, or interaction density. The cells within the matrix then specify predicted behavioral responses, such as shifts in foraging patterns, mating alliances, or conflict resolution strategies, arising from the specific genetic-social intersection. In practical applications, social state matrices illuminate how social selection favors adaptive behaviors in complex group settings. For instance, in social insects like ants, a matrix might demonstrate that individuals with cooperative genetic predispositions engage in collective foraging when group sizes are large, enhancing overall colony efficiency through division of labor, whereas smaller groups with aggressive genotypes lead to solitary scavenging. Similarly, in avian systems, matrices model parental time allocations at nests, showing how genetic factors influence divisions between guarding duties and food provisioning to optimize offspring survival. These representations highlight social selection's emphasis on cooperative equilibria over competitive dominance. The evolutionary dynamics of social state matrices incorporate feedback loops where social interactions reshape genetic frequencies across generations. Matrices evolve through social feedback mechanisms, with state transitions governed by the probability P_{ij} = f(g_i, s_j), where g_i denotes the genotype in row i, s_j the social factor in column j, and f a function capturing interaction outcomes, such as payoff adjustments from cooperative exchanges. This formulation allows tracking of how genetic variants propagate under varying social pressures, often via population-genetic models that simulate allele frequency changes. Joan Roughgarden's 2009 analysis integrates social state matrices with transactional models of social selection to forecast alliance formation in reproductive contexts. By incorporating side payments—such as resource sharing or extra-pair contributions—matrices adjust payoff structures to converge on Nash bargaining solutions, predicting stable coalitions that maximize collective fitness, as seen in pairings stabilized by mutual benefits rather than rivalry. This approach briefly references reproductive transactions as exchange-based interactions that underpin matrix predictions, without delving into their broader behavioral principles. Simulations of social state matrix dynamics provide empirical support for the emergence of stable strategies under iterated social interactions. In computational models, initial random payoff assignments evolve through repeated rounds, yielding matrices where mutual cooperation becomes a robust Nash equilibrium, demonstrating how social selection sustains prosocial behaviors over generations even amid genetic variation. These results underscore the matrices' utility in revealing long-term evolutionary stability without relying on individualistic competition.

Applications and Examples

In Non-Human Species

In social insects such as honeybees (Apis mellifera), worker sterility has evolved through mechanisms of social selection that emphasize alliance benefits and cooperative dynamics beyond kin selection alone. Workers forgo personal reproduction to support the queen and colony, gaining indirect fitness through enhanced group survival and resource allocation, where greenbeard genes—selfish genetic elements promoting recognition and cooperation among carriers—drive runaway social selection leading to increased sterility as a cooperative trait. This process aligns reproductive interests within the colony, with workers exchanging labor for inclusive benefits, as modeled in theoretical frameworks showing how such social transactions stabilize eusociality.^[13] In reptiles, parthenogenetic whiptail lizards (Cnemidophorus spp., such as C. uniparens) exemplify social selection through homosexual behaviors that function as social transactions for territory maintenance and reproductive stimulation, despite the absence of males. All-female populations engage in pseudocopulation and courtship rituals, where dominant individuals mount subordinates, triggering hormonal shifts (e.g., estradiol for receptive roles, progesterone for mounting) that increase ovulation rates—females with partners lay 2.6 egg batches compared to 0.9 alone—enhancing overall reproductive output and group cohesion for resource defense. These interactions form pair bonds that improve survival in arid habitats, illustrating how social alliances, rather than genetic exchange, drive behavioral evolution in monomorphic species.^[14] Among fish, social selection manifests in hermaphroditic shifts driven by competition for mates and territories in species like gobies (Paragobiodon echinocephalus) and anglerfish (Ceratiidae family). In coral reef gobies, bidirectional sex changes occur based on social cues, such as the removal of a dominant individual, allowing subordinates to transition from female to male (or vice versa) to form monogamous pairs and secure breeding sites, with ~80% of juveniles initially maturing as females to optimize pair formation and egg care by males. Similarly, deep-sea anglerfish exhibit extreme sexual parasitism, where dwarf males fuse to larger females as permanent sperm sources, a polyandrous strategy selected for efficient resource exchange in sparse environments, with over 100 species showing this dimorphism that prioritizes social integration over individual mating contests. These cases highlight how social hierarchies and partnerships shape gender plasticity for reproductive access.^[14] In birds, monomorphic species like ostriches (Struthio camelus) demonstrate social selection via female coalitions that negotiate egg-laying access in communal nests. Dominant females pair with territorial males and place their eggs centrally for better incubation, while subordinates contribute peripheral eggs, forming alliances that dilute predation risk and share parental duties, with males incubating up to 50 eggs from multiple females. These coalitions enhance chick survival through synchronized hatching and collective defense, where social status determines reproductive priority without strong sexual dimorphism, underscoring alliance benefits in cooperative breeding systems.^[14] A 2023 study on wild baboons (Papio cynocephalus) in the Amboseli ecosystem provides empirical evidence of social selection operating through grooming networks, revealing heritable components (h² = 0.22 for grooming given) and indirect genetic effects (IGEs) that account for 2% of variance in dyadic interactions. Among 224 adult females across 1983–2017, grooming was influenced by rank, age, kinship (e.g., mother-daughter pairs groom 1.67 times more), and group size, with positive genetic correlations between direct and indirect effects (r = 0.74), indicating that social partners' genotypes shape behavior and fitness via network position. This quantitative genetic analysis supports social selection as a driver of affiliative traits, doubling total heritability estimates when IGEs are included.^[15]

In Human Evolution and Prosociality

Social selection has played a pivotal role in human evolution by favoring traits that enhance social status and cooperation within groups. In his seminal 1989 model, Richard D. Alexander proposed a runaway process where intense competition for social status among early humans drove the expansion of brain size, enabling more sophisticated social strategies and fostering cooperative behaviors essential for group survival.^[16] This mechanism posits that individuals who excelled in navigating social alliances and competitions gained advantages in resource access and mating, amplifying selection pressures on cognitive and prosocial capacities over time. A 2022 review elaborates on this, identifying six arenas of runaway social selection—including status displays and altruism—that contributed to the unique cognitive and social complexity of Homo sapiens.^[5] Prosocial traits such as altruism and partner choice have evolved primarily through social selection, as these behaviors signal reliability and facilitate inclusion in cooperative groups. Randolph M. Nesse's 2016 target article in Behavioral and Brain Sciences argues that self-interested choices for prosocial partners create strong selective pressures, potentially leading to runaway dynamics where extreme generosity becomes advantageous for reputation and alliance formation.^[6] This process explains the prevalence of costly helping behaviors in humans, as they enhance an individual's value in social networks beyond immediate kin. Modern experimental studies, such as those using economic games, demonstrate that reputation management drives prosocial actions, with participants cooperating more when observed by potential partners.^[17] Social selection also underpins the cultural origins of human cooperation by favoring the transmission of norms that promote group cohesion, integrating with gene-culture coevolution dynamics. Cultural practices emphasizing reciprocity and fairness are selected because they improve group productivity and individual fitness through enhanced social bonds. A 2009 PNAS study highlights how cultural evolution provides broader scope for prosociality than genetic changes alone, as norms propagate rapidly and reinforce genetic predispositions for empathy and fairness.^[18] Fossil evidence from Homo sapiens sites, dating back approximately 300,000 years, shows increasing indicators of social complexity—such as shared tool technologies—aligning with this selective trajectory toward culturally mediated cooperation, with later evidence of burial practices around 100,000 years ago. The 2022 Frontiers review further connects these runaway processes to human displays of value and altruism, underscoring their role in cultural persistence.^[5]

Criticism and Debates

Critiques of Core Theory

One prominent set of critiques emerged in 2006 following Joan Roughgarden's review article proposing social selection as a replacement for sexual selection, prompting ten letters from forty evolutionary biologists published in Science. These critics, including Kate Lessells, argued that Roughgarden's formulation conflates sexual selection with broader social interactions, effectively redefining sexual selection under a new name rather than offering a genuine alternative. They further accused the theory of anthropomorphism, particularly in its portrayal of mating as cooperative "contracts" or "negotiations" akin to human economic transactions, which imposes undue human-like intentionality on animal behaviors. For instance, Troy Day, David Houle, and Locke Rowe contended that Roughgarden's use of game-theoretic models to emphasize cooperation merely restates existing evolutionary game theory concepts, such as those in Axelrod and Hamilton (1981), without advancing novel insights into mate choice dynamics.^[19] Empirical challenges highlight significant gaps in quantitative validation of social selection. Critics noted a lack of rigorous testing, with Roughgarden's examples—such as elaborate bird songs—more parsimoniously explained by traditional sexual selection mechanisms like female choice for genetic quality or runaway processes, rather than cooperative social partnering. Tommaso Pizzari pointed out that the supplementary materials in Roughgarden's review contained misrepresentations in all 17 cited cases, including overlooked evidence from comparative studies linking traits like testis size to promiscuity, which supports intrasexual competition central to sexual selection. This absence of predictive, falsifiable models has left social selection empirically underdeveloped compared to the extensive data supporting sexual selection paradigms. Theoretically, detractors argue that social selection overemphasizes cooperation at the expense of inherent conflicts in reproduction, neglecting key processes like intrasexual rivalry and Fisher's runaway selection that drive exaggerated traits. David Shuker described it as "sexual selection in disguise," where game-theoretic payoffs ultimately align with differential reproductive success based on competitive mating advantages, not purely social alliances. More recent analyses, such as Roberta Millstein's 2010 review, reinforce this by critiquing the theory's reliance on pre-1970s evolutionary assumptions about fixed sex roles and cooperation, which fail to integrate modern understandings of genetic conflict and variable parental investment.^[20] In 2019, Randolph Nesse questioned the proposed distinction between social selection and natural selection, arguing in his book that social processes shaping traits like competitive altruism are subsumed under natural selection's umbrella, rendering social selection redundant as a separate framework.

Responses and Alternative Views

In response to early criticisms of her 2006 proposal, Joan Roughgarden and collaborators published replies in Science that defended social selection as a distinct alternative to sexual selection, emphasizing cooperative game-theoretic models where reproductive success arises from mutual ecological benefits rather than competitive mate acquisition. These responses highlighted social selection's focus on offspring viability through social partnerships, positioning it as inclusive of mating dynamics but broader in scope, extending to non-mating social interactions that enhance survival and reproduction.^[21] Between 2006 and 2009, Roughgarden further clarified this distinction in subsequent publications and her book The Genial Gene, arguing that social selection subsumes elements of sexual selection while rejecting its core assumption of inherent sexual conflict, instead prioritizing transactional cooperation among individuals of any sex or orientation.^[22] Building on these foundations, Bruce Lyon and Robert Montgomerie integrated social selection into mainstream theory in their 2012 analysis, proposing it as an overarching framework—or "umbrella"—for the evolution of sexually selected traits in both males and females, where social interactions beyond reproduction drive ornamentation and weaponry.^[23] They argued that this broader social lens resolves ambiguities in Darwinian sexual selection by incorporating non-sexual competition and cooperation, supported by empirical examples from avian and mammalian species where female traits evolve via social partner preferences.^[2] More recent syntheses have formalized social selection using mathematical models of indirect genetic effects (IGEs), where an individual's genotype influences not only its own fitness but also that of social partners. A 2023 study in Science Advances demonstrated how social selection generates IGEs that accelerate adaptation and population growth in human societies, integrating these effects into quantitative equations that extend traditional natural selection frameworks without supplanting them.^[24] Alternative models, such as Randolph Nesse's 2019 hypothesis, apply social selection to human evolution by positing it as a driver of reduced reactive aggression and enhanced cooperation in tasks like hunting and warfare, without necessitating the replacement of sexual selection but rather complementing it through partner choice that favors prosocial traits.^[25] Nesse emphasized that social selection operates via preferences for cooperative individuals, fostering cultural norms and altruism in large groups. Ongoing debates reflect growing acceptance of social selection in prosociality research, where it explains cooperative behaviors in humans and other species, yet it faces resistance in traditional sexual selection fields due to perceived overlaps and challenges in empirical differentiation.^[26]

Broader Uses

In Evolutionary Biology

Social selection has been proposed as a unifying framework that encompasses sexual selection within the broader context of social competition for resources, including mates, where individuals compete through displays and behaviors that influence partner preferences. Mary Jane West-Eberhard argued that sexual selection is a specific form of social selection arising from conspecific interactions, emphasizing social response systems that drive the evolution of extreme traits via feedback between signals and receivers. This perspective highlights how mate choice and other social interactions generate selection pressures analogous to those in non-reproductive contexts, promoting traits that enhance social alliances and resource access. In the realm of altruism and kin selection, social selection provides an alternative explanation for the evolution of eusociality in insects through mechanisms like partner choice, where individuals preferentially associate with cooperative or high-quality partners, favoring traits that support group cohesion without relying solely on relatedness. For instance, in social insects such as wasps and ants, partner choice can amplify cooperative behaviors, leading to the stability of eusocial colonies by rewarding altruists with better social positions or survival benefits. Social selection also involves indirect effects, where an individual's phenotype influences the fitness of social partners, leading to heritable changes across multiple loci in structured populations. Such models reveal that social interactions generate covariance between genotypes at different loci, amplifying the role of social environments in adaptation. Links between social selection and cultural evolution appear in models by Robert Boyd and Peter Richerson, where social learning mechanisms are selected to enhance group-level fitness by allowing individuals to acquire adaptive behaviors from successful partners. In these dual-inheritance frameworks, social selection favors conformist transmission and imitation of prosocial traits, promoting cultural variants that improve collective outcomes in variable environments. This process integrates genetic and cultural inheritance, with social selection acting on learning biases that prioritize group-beneficial information. Recent extensions of social selection to human evolution emphasize runaway processes in non-cultural domains, such as cognitive and behavioral traits shaped by intergroup competition and alliance formation. These mechanisms contributed to prosociality in humans by selecting for traits that facilitate large-scale cooperation.

In Other Fields

In sociology, the concept of social selection describes how social status and stratification influence partner choice in human mate markets, often resulting in assortative mating patterns that perpetuate inequality. Research from the 2010s indicates that individuals preferentially select partners from similar socioeconomic backgrounds, with social class origins serving as a primary filter in marital decisions. For example, an analysis of British cohort data spanning 1949 to 2010 found strong persistence in assortative mating by father's social class, showing minimal weakening over six decades despite broader social changes.^[27] This process underscores how mate markets function like competitive arenas where higher-status individuals gain advantages in selecting desirable partners, reinforcing intergenerational social mobility barriers.^[28] In psychology, social selection explains conformity and ostracism within group dynamics as mechanisms for maintaining social cohesion and avoiding exclusion. Individuals adapt behaviors to align with group norms under social pressures, with emotions like shame serving as signals to conform or risk rejection. Extensions of this idea, as explored by Wrangham in 2019, link social selection to the evolution of reduced aggression in humans, positing that preferences for cooperative, non-aggressive traits in social interactions foster group stability and prosociality.^[25] This framework highlights how social selection operates through interpersonal choices, promoting traits that enhance acceptance while penalizing deviance through mechanisms like ostracism, thereby shaping psychological adaptations for group living.^[29] In economics, social selection is modeled as a market-like process that favors cooperative behaviors in interconnected networks, where individuals choose partners based on reliability and reciprocity. Studies show that in evolving networks, cooperators attract more ties, creating feedback loops that amplify prosocial outcomes over defection. For instance, integrating human social motives with network dynamics reveals that selection for cooperative partners boosts overall group cooperation, as prosocial individuals form denser, more stable connections.^[30] This analogy to economic markets emphasizes how non-random partner choices drive efficiency in resource sharing and collective action, without relying on centralized enforcement.^[31] Applications of social selection in these fields typically employ the term metaphorically, emphasizing behavioral and cultural influences rather than genetic heritability. For example, 2021 analyses of social networks demonstrate how user preferences and platform structures selectively amplify traits like trustworthiness, mimicking selection pressures in digital environments.^[32] Scholars caution against overextending the concept from its biological origins, as this risks conflating cultural processes with evolutionary imperatives and introducing pseudoscientific implications into social analyses.^[33]

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Aug 19, 2019 · On the assumption that humans benefit by cooperating in gathering, hunting, warfare and other tasks, social selection has likely been important ...
[25]
Q&A with Joan Roughgarden on the Problems with the ... - MIT Press
Feb 11, 2019 · Social selection starts with offspring production and works backwards to mating, whereas sexual selection starts with mating and implicitly ...<|control11|><|separator|>
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Social Class Origin and Assortative Mating in Britain, 1949–2010
Sep 12, 2017 · This article examines trends in assortative mating in Britain over the last 60 years. Assortative mating is the tendency for like to form a ...
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Social Class Origin and Assortative Mating in Britain, 1949–2010
Aug 7, 2025 · This paper examines trends in assortative mating in Britain over the last sixty years. Assortative mating is the tendency for like to form a ...
[28]
Runaway Social Selection for Displays of Partner Value and Altruism.
Social selection is a powerful explanation for prosociality.Randolph M. Nesse - 2016 - Behavioral and Brain Sciences 39:e47. Multilevel selection ...
[29]
Integrating social networks and human social motives to ... - PNAS
Sep 15, 2014 · ... behaviors (social influence) as well as changes in the creation, maintenance, and dissolution of network ties (social selection). Aral and ...
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Quality versus quantity of social ties in experimental cooperative ...
Nov 14, 2013 · This kind of social selection pressure can reinforce cooperation in the network, as shown by these models. However, prior theoretical work ...
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Generalized Trust and Social Selection Process - Frontiers
Social selection processes refer to the ways in which actors' characteristics (i.e., attributes and attitudes) affect network formation and changes in a given ...
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THE FALSE ALLURE OF GROUP SELECTION - Edge.org
Jun 18, 2012 · Group selection sounds like a reasonable extension of evolutionary theory and a plausible explanation of the social nature of humans.