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This chapter examines the notorious issue of group selection in behavioural ecology, one of the mainstays of the traditional levels of selection debate. The history of the group selection controversy is briefly traced. The relationship between group selection, kin selection, and evolutionary game theory is discussed. An important debate between Sober and Wilson and Maynard Smith concerning the correct way to conceptualize group selection is explored. Lastly, some arguments of L. Nunney concerning the distinction between weak and strong altruism, and how individual and group selection should be defined, are examined.

Selection is often generated by interaction with other organisms: neighbours, partners, or antagonists. The force and direction of selection in these social contexts is very generally influenced by the density and composition of the population. It may result in some degree of cooperation or helpfulness, rather than unrestricted competition among individuals. The first section here is called Selection within a single uniform population: density-dependent selection and details density regulation; density-dependent fitness; the principle of frugality; resource competition in continuous culture; r-K selection; r-K selection experiments; and selection in seasonal environments. The second section is called Selection within a single diverse population: frequency-dependent selection and describes GxG; frequency-dependent fitness; and also frequency-dependence in complex environments. The third section is about social behaviour and describes the phenotypic theory of aggression and exploitation; cross-feeding; selfish cooperation; the prisoners' dilemmas; intransitive social interactions; and time-lagged social interactions. The final section is called Kin selection and group selection and describes kin selection; kin proximity and kin choice; spite; group selection in structured populations; productivity and diversity; artificial group selection; and cultural evolution.

The term quorum sensing (QS) is used to describe communication between bacterial cells, whereby a coordinated population response is controlled by diffusible signal molecules. QS has not only been described between cells of the same species (intraspecies), but also between bacterial species (interspecies) and between bacteria and higher organisms (interkingdom). This chapter compares the evolutionary literature on animal signalling and cooperation with the microbiological literature on QS, and discusses whether bacterial QS can be considered true signalling. From an evolutionary perspective, intraspecies signalling can be explained using models such as kin selection, but explanations become more difficult when communication is described between species. It is likely that this often involves QS molecules being used as ‘cues’ by other species as a guide to future action or as coercing molecules whereby one species will ‘coerce’ another into a response.

This chapter discusses the evolution of altruism through kin-selection. There is a great deal of evidence that humans and other animals are disposed to behave in accordance with Hamilton’s rule, sacrificing their interests for the sake of their kin and favoring those to whom they are most closely related, especially relatives with the highest reproductive potential. Kin-selection is a complex process that is widely misunderstood. The evidence suggests that humans (and many other animals) rely on three main cues to distinguish their kin from others—similarity (especially how much others look and smell like them), familiarity, and proximity (how close to them they reside). Because kin recognition mechanisms are designed in imperfect ways, people may end up helping others who look and act like their kin, thus contributing little or nothing to the propagation of their genes and rendering the behaviors genetically altruistic.

This chapter examines inclusive fitness, which is the conceptual paradigm that has dominated the field for the past three decades. This paradigm is shown to be wanting as a framework to understand how social wasps evolved.

This chapter examines cooperation between two species and how cooperation among related individuals of one species can also help maintain cooperation between species. It presents some examples of between-species cooperation, the evolutionary tradeoffs that can undermine such cooperation, and opportunities for improvement. The chapter begins by showing that cooperation and so-called cheating commonly occur between two species. It then considers how conflict evolves and how two-species partnerships may be improved such that they will be useful in agriculture. It also explores symbiotic nitrogen fixation and the dilemma termed “tragedy of the commons,” the link between kin selection and within-species cooperation, and microbial analogs of kin selection and rhizobial mutualism. Finally, the chapter discusses the sanctions hypothesis that explains the nature of microbial cooperation with plants, along with other opportunities for improved two-species cooperation.

This chapter considers the mechanisms by which aposematic signals might evolve and be maintained. Of particular importance are the roles of spatial aggregation and kin selection in the evolution of such signals, and the co-evolution of defence and signals of that defence. The initial evolution of aposematism is particularly interesting and challenging, since aposematic signals are expected to be more effective when they are commonplace, thus an initial rare mutant might be expected to be at a disadvantage.

Patients are phenotypes; thus all medical conditions are a product of genes and the environment. One genotype can produce many phenotypes depending on the environments encountered. Such phenotypic plasticity promotes reproductive success by creating a better fit between the genotype and the environment. Evolutionary insights into kin selection, life history, parental investment, and sexual selection help us to understand: the origins of child abuse and homicide in step-families; deadbeat dads; attachment disorders; failure to thrive; female infanticide; excess male mortality from accidents, suicide, and disease; risky behaviour; immunosuppression; reproductive cancer; marital violence; and genital cutting. Many of these problems reflect reproductive conflicts of interest between individuals. Other conflicts occur within individuals and involve life history trade-offs. Conflicts of interest within and between individuals constrain natural selection, and prevent an optimal world wherein adaptation is maximized at all levels simultaneously.

This chapter contains a discussion of Maynard Smith’s conceptual distinction between kin and group selection. The author discusses the design and experimental study of kin selection for and against cannibalism as a test of the definitional distinction. The fallacy that societies are vulnerable to cheaters is discussed along with the concept of a “kin-selection mutation balance.” The results of models with three levels of selection as well as models of the effect of inbreeding on kin selection are presented. The synergistic coevolution of mating system and sociality are illustrated and the underlying processes governing the run-away evolution of sociality are discussed. The advantage of the multilevel selection perspective over the inclusive fitness perspective is illustrated by drawing from counter-factual predictions of inclusive fitness theory and its inability to account for underlying processes of genetic change.

When do we care for others as we care for ourselves? William Hamilton showed that we should be expected to care for our family members in proportion to our degree of relationship to them. Such reasoning explains why eusociality evolved independently at least twelve times in the order Hymenoptera, which includes ants, bees, and wasps, but only three times elsewhere in the animal kingdom. It also verifies Thomas Hobbes' answer to the question: Why cannot mankind live sociably one with another as bees or ants?

The phenotypes of those individuals with which an focal individual interacts often influences the trait value in the focal individual. Maternal effects is a classic example of this phenomena, as is fitness. If these traits are heritable, then the selection response depends on both the change in the direct effects influencing a target trait and the associative effects contributed by interacting individuals. In such a setting, the breeder's equation no longer holds, as the problem is now a multiple trait one. This chapter examines the theory of response under models with both direct and associative effects, which can lead to a reversed response (a trait selected to increase instead decreases). The evolution of behavioral traits, including the evolution of altruism, is best handled using this approach. Further, kin and group selection follow as special cases of the gerenal model under multilevel selection. This chapter also examines how mixed models can be used estimate model parameters.

In group-structured populations in which some other assumptions are satisfied, kin and group selectionist methods provide formally equivalent conditions for change. However, this only shows an equivalence between two statistical methodologies, and this is compatible with there being a real, causal distinction between kin and group selection processes. This chapter pursues a Hamilton-inspired, population-centred approach to drawing that distinction, on which the differences between kin and group selection are differences of degree in the structural properties of populations. The relevant properties are K, the overall degree to which genealogical kin interact differentially, and G, the overall degree to which the population contains stable, internally integrated, and externally isolated social groups. A spatial metaphor (‘K-G space’) provides a useful framework for thinking about these differences.

In this chapter I distinguish between two basic forms of altruism, which I call biological and psychological altruism, and explain how dispositions to emit each type evolved in the human species. Biological forms of altruism are defined in terms of the consequences of helping behaviors. They contribute to the survival and reproductive success of recipients at a cost to the survival and reproductive success of donors. Psychological forms of altruism are defined in terms of the motives and intentions of actors. They are aimed at improving the welfare of recipients as an end in itself. A form of conduct that has been labeled reciprocal altruism does not really qualify as biologically altruistic because it produces return benefits to donors. Mental mechanisms that evolved through kin selection are not very precisely designed. When people help others who resemble their kin, they may behave in biologically and genetically altruistic ways. Evolutionary theorists disagree about how mental mechanisms that dispose people to help strangers anonymously with no possibility of return benefits evolved. Researchers have concluded that in some contexts, people may be genuinely motivated to help others as an end in itself. Studies have produced the following findings. People are willing to help others in emergencies without any apparent concern for their own welfare. Empathy engenders the motive to help victims as an end in itself, rather than as a means of reducing vicariously-experienced distress, enhancing one’s public image, making one feel good about oneself, and so on. Identifying with a groups disposes people to sacrifice their interests for the sake of the group. People experience moral emotions that engender altruistic motives. Higher order cognitive abilities interact with more primitive emotional responses to structure moral emotions such as sympathy in ways that give rise to increasingly effective forms of altruism.

This chapter investigates recent proposals that a kin-selected communication system was adaptive in human evolution, and that in turn, interactions between closely-related individuals, particularly mothers and infants, drove the evolution of (proto)language. It argues that a proposed link between kin communication, teaching, and linguistic complexity is very weak; and that altruism is not characteristic of language use. The chapter is organized as follows. Section 5.2 examines the idea that protolanguage evolved for pedagogical purposes vital to a child's survival. Section 5.3 considers the proposed evolution of linguistic complexity out of either infant or maternal vocalizations. Section 5.4 questions the idea that language equates to altruistic information exchange. Section 5.5 concludes that a kin selection scenario has no explanatory power in investigations of the evolution of language.

This chapter explores the modeling of multilevel selection (MLS) – and the related concepts of group selection and kin selection – using variance partitioning methods, using the Price equation to elucidate basic issues within MLS theory. An expansion of this theory, based on contextual analysis and direct fitness, is used to show that kin selection and MLS selection have the same mathematical roots, although they are not identical. Kin selection theory is oriented towards identifying the optimal group and individual level traits that maximize the fitness of an organism, while MLS theory is oriented towards identifying the rate of evolution of the group and individual level traits in a specified situation. Because of these differences, kin selection and group selection can be considered as complementary approaches. The chapter also addresses why heritable variation at one level often bears little relation to heritable variation at other levels. It is shown that interactions among units (e.g., individuals) cannot contribute to a response to selection at that level, but can contribute to response to selection at a higher level (e.g., the population). Thus, the response to selection at one level can be qualitatively different than the response to selection at other levels.

Adaptations are the products of natural selection—traits that evolved because they proved useful at some level. Often adaptations evolved because they enhanced the survival or reproductive output of individuals, but selection can also operate at other levels—genes, individuals, populations, and species. Sometimes a genetic change has positive effects on all levels. A mutation that increases the survival of its carrier would increase in frequency; populations that become fixed for that allele may be less prone to extinction, which in turn may increase the longevity of that species. Other times there can be conflicting fitness effects at the different levels. This chapter explores the power of natural selection in shaping the living world by investigating the complexities of multilevel selection, biological solutions to heterogeneity and unpredictability in the environment, and how interactions between species can shape evolution. However, the chapter starts by investigating factors that may constrain adaptive evolution.

This chapter introduces a 1974 paper that represents Richard D. Alexander's first exposition of general theory for the evolution of social behavior across all animals, including humans. Alexander's paper, integrating nepotism, reciprocity, and his new idea—parental manipulation—tackles the evolution of sociality in insects. It follows on from George Williams's critique of loose group selection thinking and on the work of William Hamilton and Robert Trivers in building an individual-centered theory. The chapter considers Alexander's argument that parents would win in conflicts with their offspring and that kin selection on offspring was not the primary force in eusociality. It includes an excerpt from his paper, entitled “The evolution of social behavior” and published in the Annual Review of Ecology and Systematics.

In this chapter we look at patterns of coexistence and mutual support in symbiosis that appear at the most complex levels in the biology of animals, starting with a brief discussion of how evolution governs interrelationships between species. The chapter proceeds to examine recent discoveries of more intimate roles of sharing resources and altruistic interactions of individuals in populations of social animals. Kin selection’s role in inclusive fitness has been especially touted in eusocial species such as ants. Now this theory appears limited in light of new and perhaps revolutionary insights on various mechanisms that appear to trigger mutualistic social behavior. Reciprocal altruism’s uncanny relationship to the strategic game, Prisoner’s Dilemma, now appears more important than ever in explaining cooperative behavior in diverse animal groups. Ongoing research on social interactions of our nearest relatives among the great apes strongly indicates that empathy, sympathy, and rudiments of morality such as fairness evolved in common ancestors of higher primates that gave rise to human beings. This heritage has led to the threshold of the fractal self.

Nepotism is inherent in both humans and animals. Some animal societies are more or less nepotistic than others, but there is no society in which individuals are biased in favor of non-kin and against their kin. The reason nepotism exists is a phenomenon called kin selection. By helping relatives with whom they share genes, individuals increase the probability that their own genes will be passed on to the next generation. Without information on kinship, it is virtually impossible to understand how any animal or human society is organized and why the individuals in it behave the way they do. This chapter, which examines nepotism and politics among rhesus macaques, first discusses Sigmund Freud's explanation of how sex between family members contributes to human behavior. It looks at incest and dispersal, the origins of same-sex bonding, rhesus macaques' social tolerance of their relatives and other individuals, and their altruism.