22273718
Genetic polymorphisms between altruism and selfishness close to the Hamilton threshold rb = c
Genes that in certain conditions make their carriers altruistic are being identified, and altruism and selfishness have shown to be heritable in man. This raises the possibility that genetic polymorphisms for altruism/selfishness exist in man and other animals. Here we characterize some of the conditions in which genetic polymorphisms may occur. We show for dominant or recessive alleles how the positions of stable equilibria depend on the benefit to the recipient, b, and the cost to the altruist, c, for diploid altruists helping half or full sibs, and haplodiploid altruists helping sisters. Stable polymorphisms always occur close to the Hamilton threshold rb = c. The position of the stable equilibrium moves away 0 or 1 with both increases in c, the cost paid by the altruist, and increasing divergence from the Hamilton threshold, and alleles for selfishness can reach frequencies around 50%. We evaluate quantitative estimates of b, c and r from field studies in the light of these predictions, but the values do not fall in the regions where genetic polymorphisms are expected. Nevertheless, it will be interesting to see as genes for altruism are discovered whether they are accompanied by alternate alleles for selfishness.
2525479
The role of D4 receptor gene exon III polymorphisms in shaping human altruism and prosocial behavior
Human beings are an extraordinarily altruistic species often willing to help strangers at a considerable cost (sometimes life itself) to themselves. But as Darwin noted “… he who was ready to sacrifice his life, as many a savage has been, rather than betray his comrades, would often leave no offspring to inherit his noble nature.” Hence, this is the paradox of altruism. Twin studies have shown that altruism and other prosocial behavior show considerable heritability and more recently a number of candidate genes have been identified with this phenotype. Among these first provisional findings are genes encoding elements of dopaminergic transmission. In this article we will review the evidence for the involvement of one of these, the dopamine D4 receptor (DRD4) gene, in shaping human prosocial behavior and consider the methodologies employed in measuring this trait, specific molecular genetic findings and finally, evidence from several Gene × Environment (G × E) studies that imply differential susceptibility of this gene to environmental influences.
5793274
Epigenetic (re)programming of caste-specific behavior in the ant Camponotus floridanus
Epigenetic control of caste-specific foraging In carpenter ants, separate behavioral classes, known as castes, are determined by the epigenetic regulation of genes. Simola et al. treated ants of different castes with drugs that affected histone acetylation. Reducing histone acetylation stimulated scouting and foraging behavior. The foraging and scouting behaviors of young ants were permanently changed by directly injecting their brains with histone acetylation inhibitors. Science, this issue p. 10.1126/science.aac6633 Changes in histone acetylation explain differences in the foraging and scouting patterns of different castes of carpenter ants. INTRODUCTION Eusocial insects, such as ants, live a communal lifestyle within colonies of close genetic relatives. Colony members are organized into castes defined by behavioral and, in some species, morphological traits. This caste system allows for colonial division of labor and is a key adaptation of eusocial insects. However, there is limited understanding of the molecular regulation of caste-specific behavior and the principles underlying division of labor. In the carpenter ant Camponotus floridanus, morphologically distinct worker castes called minors and majors exhibit unique patterns of histone posttranslational modifications, including lysine acetylation regulated by CBP [cyclic adenosine monophosphate response element–binding protein (CREB) binding protein], a conserved histone acetyltransferase (HAT). RATIONALE Because chromatin regulators such as CBP have been associated with caste-specific traits, we tested whether caste-specific behavioral states in eusocial insects are functionally regulated via epigenetic mechanisms. We assessed innate differences in foraging and scouting (by the lead forager), classic altruistic behaviors of eusocial systems, between minor and major worker castes in C. floridanus. We examined whether CBP and histone deacetylases (HDACs) functionally regulate caste-specific foraging and scouting behaviors. Further, we tested whether caste-specific behavioral states may be reprogrammed through epigenomic manipulations. RESULTS C. floridanus minors and majors exhibited innate differences in foraging and scouting behaviors, with minors performing the bulk of both activities. Treatments with small-molecule inhibitors of class I and II HDAC activity (HDACi) enhanced foraging and scouting. This gain of function was suppressed by treatment with a small-molecule HAT inhibitor of CBP (HATi). Transcriptome and chromatin analyses in the brains of minors treated with HATi and HDACi revealed changes in genes linked to regions of hyperacetylated histone H3 Lys27 (a lysine targeted by CBP) near CBP binding sites. Although untreated majors rarely foraged, suppression of histone deacetylation by injection of HDACi or small interfering RNAs (siRNAs) against the HDAC-encoding gene Rpd3 into young major brains was sufficient to induce and sustain minor-like foraging and scouting for up to 50 days. Strikingly, coinjection of CBP HATi suppressed HDACi-induced foraging and scouting in majors. CONCLUSION Caste-specific foraging and scouting behaviors are tightly linked to morphology and are likely regulated epigenetically by the balance between CBP-mediated acetylation and HDAC-mediated deacetylation of histones in the ant central brain. Thus, behavioral plasticity can be manipulated in the ant C. floridanus by pharmacological and genetic tools that target chromatin regulatory enzymes to stimulate, inhibit, and reprogram behavior. These findings reveal the epigenome as a likely substrate underlying caste-based division of labor in eusocial insects. Furthermore, in light of the conserved role of CBP in learning and memory in both invertebrates and mammals, these data suggest that CBP-mediated histone acetylation may similarly facilitate the complex social interactions found in vertebrate species. An epigenetic model for division of labor. Left: Workers were injected at eclosion and tested for foraging activity. HDAC inhibition (HDACi) with chromatin drugs or siRNA enhanced foraging; HATi suppressed foraging. Right: Minor and major workers express distinct behavioral ontogenies. Minors forage earlier in life and with greater intensity than majors. HDACi in majors stimulated minor-like foraging behavior, a gain of function suppressed by HATi treatment. Eusocial insects organize themselves into behavioral castes whose regulation has been proposed to involve epigenetic processes, including histone modification. In the carpenter ant Camponotus floridanus, morphologically distinct worker castes called minors and majors exhibit pronounced differences in foraging and scouting behaviors. We found that these behaviors are regulated by histone acetylation likely catalyzed by the conserved acetyltransferase CBP. Transcriptome and chromatin analysis in brains of scouting minors fed pharmacological inhibitors of CBP and histone deacetylases (HDACs) revealed hundreds of genes linked to hyperacetylated regions targeted by CBP. Majors rarely forage, but injection of a HDAC inhibitor or small interfering RNAs against the HDAC Rpd3 into young major brains induced and sustained foraging in a CBP-dependent manner. Our results suggest that behavioral plasticity in animals may be regulated in an epigenetic manner via histone modification.
13867477
Genetic Variation in Preferences for Giving and Risk Taking
In this paper, we use the classical twin design to provide estimates of genetic and environmental influences on experimentally elicited preferences for risk and giving. Using standard methods from behavior genetics, we find strong prima facie evidence that these preferences are broadly heritable and our estimates suggest that genetic differences explain approximately twenty percent of individual variation. The results thus shed light on an important source of individual variation in preferences, a source that has hitherto been largely neglected in the economics literature.
19588145
Behavioral genetic analyses of prosocial behavior in adolescents.
Prosocial behavior is an important aspect of normal social and psychological development. Adult and child twin studies typically estimate the heritability of prosocial behavior to be between 30 and 50%, although relatively little is known about genetic and environmental influences upon prosocial behavior in adolescence. We therefore examined reports of prosocial behavior in a large longitudinal family study of 1160 adolescent twin pairs (aged between 13 and 19 years). Prosocial behavior was assessed at two time points by self-report and at the second time point by additional parent-ratings using the Strengths and Difficulties Questionnaire (SDQ; Goodman, 1997). Adolescent females were reported to be significantly more prosocial than males (p < .001). Univariate analyses primarily showed moderate heritability and large nonshared environmental influences. There was a moderate genetic correlation between self- and parent-reported prosocial behaviour, suggesting that both types of rater were tapping into genetically overlapping constructs. Longitudinal analyses revealed that continuity was largely explained by genes. Unique environmental influences were predominantly time-specific and were the major source of individual differences.
145514631
The genetics of morality and prosociality
Genetically informed research of phenotypes related to morality has proliferated rapidly in the last few years, sparking paradigm shifts from theories based solely on socialization toward ones integrating biological influences. Here, we review recent genetic research in the area of morality that has received the most attention in genetic studies: prosociality — positive emotions, attitudes, and behaviors directed toward others. Individual differences in prosociality emerge early in life, increase in heritability as children develop, and are related to variation in genes regulating neurotransmitter systems central to social affect, cognition, and behavior. The majority of molecular genetic studies have been candidate-based, however genome-wide studies are emerging, with the potential to elucidate novel biological pathways associated with individual differences in morality.
18020445
Prosocial behavior from early to middle childhood: genetic and environmental influences on stability and change.
Prosocial behavior is important for the functioning of society. This study investigates the extent to which environment shared by family members, nonshared environment, and genetics account for children's prosocial behavior. The prosocial behavior of twins (9,424 pairs) was rated by their parents at the ages of 2, 3, 4, and 7 and by their teachers at age 7. For parent ratings, shared environmental effects decreased from .47 on average at age 2 to .03 at age 7, and genetic effects increased from .32 on average to .61. The finding of weak shared environmental effects and large heritability at age 7 was largely confirmed through the use of teacher ratings. Using longitudinal genetic analyses, the authors conclude that genetic effects account for both change and continuity in prosocial behavior and nonshared environment contributes mainly to change.
30812931
Genetic and environmental contributions to pro-social attitudes: a twin study of social responsibility
Although 51 twin and adoption studies have been performed on the genetic architecture of antisocial behaviour, only four previous studies have examined a genetic contribution to pro–social behaviour. Earlier work by the author with the University of London Institute of Psychiatry Adult Twin Register found that genes contributed approximately half of the variance to measures of self–report altruism, empathy, nurturance and aggression, including acts of violence. The present study extends those results by using a 22–item Social Responsibility Questionnaire with 174 pairs of monozygotic twins and 148 pairs of dizygotic twins. Forty–two per cent of the reliable variance was due to the twins' genes, 23% to the twins' common environment and the remainder to the twins' non–shared environment.
13903725
Altruism and aggression: the heritability of individual differences.
Five questionnaires measuring altruistic and aggressive tendencies were completed by 573 adult twin pairs of both sexes from the University of London Institute of Psychiatry Volunteer Twin Register. The questionnaires measured altruism, empathy, nurturance, aggressiveness, and assertiveness. The intraclass correlations for the five scales, respectively, were .53, .54, .49, .40, and .52 for 296 monozygotic pairs, and .25, .20, .14, .04, and .20 for 179 same-sex dizygotic pairs, resulting in broad heritability estimates of 56%, 68%, 70%, 72%, and 64%. Additional analyses, using maximum-likelihood model-fitting, revealed approximately 50% of the variance on each scale to be associated with genetic effects, virtually 0% with the twins' common environment, and the remaining 50% with each twins' specific environment and/or error associated with the test. Correcting for the unreliability in the tests raised the maximum-likelihood heritabilities to approximately 60%. Age and sex differences were also found: altruism increased over the age span from 19 to 60, whereas aggressiveness decreased, and, at each age, women had higher scores than men on altruism and lower scores on aggressiveness.
1285705
The development of prosocial behaviour in children and adolescents: a twin study.
BACKGROUND
Childhood psychopathology is associated with both high and low levels of prosocial behaviour. It has been proposed that the development of prosocial behaviour shows emerging and consolidating individual differences as children grow older. The influences on these individual differences have not previously been examined in children and adolescents using multiple raters in a genetically informative design.


METHODS
Twin data from 682 families based on parent and teacher reports were used to examine the genetic and environmental influences on prosocial behaviour in 5-16-year-olds. Effects of sex, age and rater were examined.


RESULTS
There were no significant differences in the magnitude of genetic and environmental influence on male and female prosocial behaviour. Declining common environment and increasing genetic influences were seen with age. This emerged as a trend in parent data and reached statistical significance in teacher data. When parent and teacher data were examined together in a rater bias model significant bias acting on the parent ratings emerged, in keeping with previous discrepancies between parental and observational measures. There was overlap in the phenotype rated by parents and teachers, with a highly heritable common underlying phenotype.


CONCLUSIONS
The influences on the distribution of prosocial behaviour in children and adolescents show declining shared environmental and increasing genetic influences with age. Parental assessments of prosocial behaviour show significantly higher scores than teacher reports and whilst there is overlap in the phenotype rated by parents and teachers, parents show significant bias in their ratings.
2342035
Altruism and Antisocial Behavior: Independent Tendencies, Unique Personality Correlates, Distinct Etiologies
The relationship between altruism and antisocial behavior has received limited attention because altruism and antisocial behavior tend to be studied and discussed in distinct literatures. Our research bridges these literatures by focusing on three fundamental questions. First, are altruism and antisocial behavior opposite ends of a single dimension, or can they coexist in the same individual? Second, do altruism and antisocial behavior have the same or distinct etiologies? Third, do they stem from the same or from distinct aspects of a person's personality? Our findings indicate that altruism and antisocial behavior are uncorrelated tendencies stemming from different sources. Whereas altruism was linked primarily to shared (i.e., familial) environments, unique (i.e., nonfamilial) environments, and personality traits reflecting positive emotionality, antisocial behavior was linked primarily to genes, unique environments, and personality traits reflecting negative emotionality and a lack of constraint.
2059321
General kin selection models for genetic evolution of sib altruism in diploid and haplodiploid species.
A population genetic approach is presented for general analysis and comparison of kin selection models of sib and half-sib altruism. Nine models are described, each assuming a particular mode of inheritance, number of female inseminations, and Mendelian dominance of the altruist gene. In each model, the selective effects of altruism are described in terms of two general fitness functions, A(beta) and S(beta), giving respectively the expected fitness of an altruist and a nonaltruist as a function of the fraction of altruists beta in a given sibship. For each model, exact conditions are reported for stability at altruist and nonaltruist fixation. Under the Table 3 axions, the stability conditions may then be partially ordered on the basis of implications holding between pairs of conditions. The partial orderings are compared with predictions of the kin selection theory of Hamilton.
24012518
The evolution of altruism between siblings: Hamilton's rule revisited.
This paper explores the validity of Hamilton's rule in the case of other-only altruism in which the benefits are shared by other members of the sibling group excluding the donor. It presents a model of competition between two alleles which code for different kinds of altruism. It derives a simple replicator equation for allele frequencies under conditions of strong selection. This equation does not depend on the size of the sibling group. In mathematical form, the equation is similar to Hamilton's original rule in the case of inbreeding, although the causal mechanism is different. The paper derives a simple criterion to determine whether there will be a polymorphism in which both alleles coexist permanently. Such an event is rare and victory will normally go to the allele with the higher value of 1/2b-c, where b is the total benefit which an offspring confers on its siblings and c is the cost to the donor. The paper also considers how an offspring will behave in particular circumstances. Using a specialized version of the basic model, it shows how, in the absence of polymorphism, natural selection should take the system towards the point of 50% marginal altruism. With this type of altruism, an offspring will perform any act for which the expected cost to the donor is at most half the expected benefit to its siblings. Acts which do not satisfy this criterion are not performed. This accords with Haldane's quip that he would sacrifice his own life for two of his brothers, but not for less. Numerical simulation is used to explore these issues in greater depth. The paper also examines briefly the implications of heterozygote advantage for Hamilton's rule. It concludes with a brief discussion of the connection between other-only altruism and whole-group altruism, in which the donor gains some benefit from its actions.
2815528
Selfishness and altruism can coexist when help is subject to diminishing returns
Altruism and selfishness are 30–50% heritable in man in both Western and non-Western populations. This genetically based variation in altruism and selfishness requires explanation. In non-human animals, altruism is generally directed towards relatives, and satisfies the condition known as Hamilton's rule. This nepotistic altruism evolves under natural selection only if the ratio of the benefit of receiving help to the cost of giving it exceeds a value that depends on the relatedness of the individuals involved. Standard analyses assume that the benefit provided by each individual is the same but it is plausible in some cases that as more individuals contribute, help is subject to diminishing returns. We analyse this situation using a single-locus two-allele model of selection in a diploid population with the altruistic allele dominant to the selfish allele. The analysis requires calculation of the relationship between the fitnesses of the genotypes and the frequencies of the genes. The fitnesses vary not only with the genotype of the individual but also with the distribution of phenotypes amongst the sibs of the individual and this depends on the genotypes of his parents. These calculations are not possible by direct fitness or ESS methods but are possible using population genetics. Our analysis shows that diminishing returns change the operation of natural selection and the outcome can now be a stable equilibrium between altruistic and selfish alleles rather than the elimination of one allele or the other. We thus provide a plausible genetic model of kin selection that leads to the stable coexistence in the same population of both altruistic and selfish individuals. This may explain reported genetic variation in altruism in man.
1232702
Evolution of discrimination in populations at equilibrium between selfishness and altruism.
Where there is genetically based variation in selfishness and altruism, as in man, altruists with an innate ability to recognise and thereby only help their altruistic relatives may evolve. Here we use diploid population genetic models to chart the evolution of genetically-based discrimination in populations initially in stable equilibrium between altruism and selfishness. The initial stable equilibria occur because help is assumed subject to diminishing returns. Similar results were obtained whether we used a model with two independently inherited loci, one controlling altruism the other discrimination, or a one locus model with three alleles. The latter is the opposite extreme to the first model, and can be thought of as involving complete linkage between two loci on the same chromosome. The introduction of discrimination reduced the benefits obtained by selfish individuals, more so as the number of discriminators increased, and selfishness was eventually eliminated in some cases. In others selfishness persisted and the evolutionary outcome was a stable equilibrium involving selfish individuals and both discriminating and non-discriminating altruists. Heritable variation in selfishness, altruism and discrimination is predicted to be particularly evident among full sibs. The suggested coexistence of these three genetic dispositions could explain widespread interest within human social groups as to who will and who will not help others. These predictions merit experimental and observational investigation by primatologists, anthropologists and psychologists.
83585826
On relatedness and adaptive topography in kin selection
Hamilton (1964a, b) constructed the verbal theoretical basis of modern kin selection theory which states that potentially “altruistic” individuals evolve to value their relatives according to the closeness of their genetic relatedness. In those fundamental papers, Hamilton restructed the brood selection models of Haldane (1932, 1955) and Williams and Williams (1957), and proposed the following criterion under which a gene for altruism may be expected to increase,
142125120
Foundations of Social Evolution
This is a treatment of one of the central problems in evolutionary biology, the evolution of social co-operation and conflict. Steven Frank tackles the problem with a combination of approaches: game theory, classical models of natural selection, quantitative genetics, and kin selection. He unites these with economic thought: a theory of model formation and comparative statics, the development of simple methods for analyzing complex problems, and notions of information and rationality. The text begins by developing the three measures of value used in biology - marginal value, reproductive value, and kin selection. It then combines these measures into a coherent framework, providing a unified analysis of social evolution in its full ecological and demographic context. Frank also extends the theory of kin selection by showing that relatedness has two distinct meanings. The first is a measure of information about social partners, with close affinity to theories of correlated equilibrium and Bayesian rationality in economic game theory. The second is a measure of the fidelity by which characters are transmitted to future generations - an extended notion of heritability. Throughout, Fran
45861755
A GENERAL MODEL FOR KIN SELECTION
Inclusive fitness theory is central to our understanding of the evolution of social behavior. By showing the importance of genetic transmission through nondescendent relatives, it helps to explain the evolution of reproductively altruistic behaviors, such as those observed in the social insects. Inclusive fitness thinking is quantified by Hamilton's rule, but Hamilton's rule has often been criticized for being inexact or insufficiently general. Here I show how adopting a genic perspective yields a very general version that remains pleasingly simple and transparent.
12215071
The Robustness of Hamilton’s Rule with Inbreeding and Dominance: Kin Selection and Fixation Probabilities under Partial Sib Mating
Assessing the validity of Hamilton’s rule when there is both inbreeding and dominance remains difficult. In this article, we provide a general method based on the direct fitness formalism to address this question. We then apply it to the question of the evolution of altruism among diploid full sibs and among haplodiploid sisters under inbreeding resulting from partial sib mating. In both cases, we find that the allele coding for altruism always increases in frequency if a condition of the form 
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10200688
Group selection and inclusive fitness are not equivalent; the Price equation vs. models and statistics.
It is often suggested that any group selection model can be recast in terms of inclusive fitness. A standard reference to support that claim is "'Quantitative genetics, inclusive fitness, and group selection" by Queller (1992) in the American Naturalist 139 (3), 540-558. In that paper the Price equation is used for the derivation of this claim. Instead of a general derivation, we try out a simple model. For this simple example, we find that the result does not hold. The non-equivalence of group selection and kin selection is therefore not only an important finding in itself, but also a case where the use of the Price equation leads to a claim that is not correct. If results that are arrived at with the Price equation are not correct, they can typically be repaired by adding extra assumptions, or explicitly stating implicit ones. We give examples with relatively mild and with less mild extra assumptions. We also discuss why the Price equation is often referred to as dynamically insufficient, and we try to find out what Price's theorem could be.
25474126
Hamilton's rule and the causes of social evolution
Hamilton's rule is a central theorem of inclusive fitness (kin selection) theory and predicts that social behaviour evolves under specific combinations of relatedness, benefit and cost. This review provides evidence for Hamilton's rule by presenting novel syntheses of results from two kinds of study in diverse taxa, including cooperatively breeding birds and mammals and eusocial insects. These are, first, studies that empirically parametrize Hamilton's rule in natural populations and, second, comparative phylogenetic analyses of the genetic, life-history and ecological correlates of sociality. Studies parametrizing Hamilton's rule are not rare and demonstrate quantitatively that (i) altruism (net loss of direct fitness) occurs even when sociality is facultative, (ii) in most cases, altruism is under positive selection via indirect fitness benefits that exceed direct fitness costs and (iii) social behaviour commonly generates indirect benefits by enhancing the productivity or survivorship of kin. Comparative phylogenetic analyses show that cooperative breeding and eusociality are promoted by (i) high relatedness and monogamy and, potentially, by (ii) life-history factors facilitating family structure and high benefits of helping and (iii) ecological factors generating low costs of social behaviour. Overall, the focal studies strongly confirm the predictions of Hamilton's rule regarding conditions for social evolution and their causes.
2136910
The genetical evolution of social behaviour. II.
Grounds for thinking that the model described in the previous paper can be used to support general biological principles of social evolution are briefly discussed. Two principles are presented, the first concerning the evolution of social behaviour in general and the second the evolution of social discrimination. Some tentative evidence is given. More general application of the theory in biology is then discussed, particular attention being given to cases where the indicated interpretation differs from previous views and to cases which appear anomalous. A hypothesis is outlined concerning social evolution in the Hymenoptera; but the evidence that at present exists is found somewhat contrary on certain points. Other subjects considered include warning behaviour, the evolution of distasteful properties in insects, clones of cells and clones of zooids as contrasted with other types of colonies, the confinement of parental care to true offspring in birds and insects, fights, the behaviour of parasitoid insect larvae within a host, parental care in connection with monogyny and monandry and multi-ovulate ovaries in plants in connection with wind and insect pollination.
28775744
THE EFFECTS OF SELECTION AND GENETIC DRIFT ON THE GENOMIC DISTRIBUTION OF SEXUALLY ANTAGONISTIC ALLELES
Sexual antagonism (SA) occurs when an allele that is beneficial to one sex, is detrimental to the other. This conflict can result in balancing, directional, or disruptive selection acting on SA alleles. A body of theory predicts the conditions under which sexually antagonistic mutants will invade and be maintained in stable polymorphism under balancing selection. There remains, however, considerable debate over the distribution of SA genetic variation across autosomes and sex chromosomes, with contradictory evidence coming from data and theory. In this article, we investigate how the interplay between selection and genetic drift will affect the genomic distribution of sexually antagonistic alleles. The effective population sizes can differ between the autosomes and the sex chromosomes due to a number of ecological factors and, consequently, the distribution of SA genetic variation in genomes. In general, we predict the interplay of SA selection and genetic drift should lead to the accumulation of SA alleles on the X in male heterogametic (XY) species and, on the autosomes in female heterogametic (ZW) species, especially when sexual competition is strong among males.
36637363
Kin Selection–Mutation Balance: A Model for the Origin, Maintenance, and Consequences of Social Cheating
Social conflict, in the form of intraspecific selfish “cheating,” has been observed in a number of natural systems. However, a formal, evolutionary genetic theory of social cheating that provides an explanatory, predictive framework for these observations is lacking. Here we derive the kin selection–mutation balance, which provides an evolutionary null hypothesis for the statics and dynamics of cheating. When social interactions have linear fitness effects and Hamilton’s rule is satisfied, selection is never strong enough to eliminate recurrent cheater mutants from a population, but cheater lineages are transient and do not invade. Instead, cheating lineages are eliminated by kin selection but are constantly reintroduced by mutation, maintaining a stable equilibrium frequency of cheaters. The presence of cheaters at equilibrium creates a “cheater load” that selects for mechanisms of cheater control, such as policing. We find that increasing relatedness reduces the cheater load more efficiently than does policing the costs and benefits of cooperation. Our results provide new insight into the effects of genetic systems, mating systems, ecology, and patterns of sex-limited expression on social evolution. We offer an explanation for the widespread cheater/altruist polymorphism found in nature and suggest that the common fear of conflict-induced social collapse is unwarranted.
2542394
A Quantitative Test of Hamilton's Rule for the Evolution of Altruism
A study of experimental evolution in simulated groups of foraging robots demonstrates that their propensity to behave altruistically depends on their genetic relatedness (similarity), and the costs and benefits associated with altruistic behavior.
1457512
Kin selection and cooperative courtship in wild turkeys
In the few species of birds in which males form display partnerships to attract females, one male secures most or all of the copulations. This leads to the question of why subordinate males help in the absence of observable reproductive benefits. Hamilton's concept of kin selection, whereby individuals can benefit indirectly by helping a relative, was a crucial breakthrough for understanding apparently altruistic systems. However in the only direct test of kin selection in coordinated display partnerships, partners were unrelated, discounting kin selection as an explanation for the evolution of cooperation. Here I show, using genetic measures of relatedness and reproductive success, that kin selection can explain the evolution of cooperative courtship in wild turkeys. Subordinate (helper) males do not themselves reproduce, but their indirect fitness as calculated by Hamilton's rule more than offsets the cost of helping. This result confirms a textbook example of kin selection that until now has been controversial and also extends recent findings of male relatedness on avian leks by quantifying the kin-selected benefits gained by non-reproducing males.