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This chapter examines the notion that humans became cooperative because in our ancestral environments we interacted frequently with the same group of close kin, among whom tit-for-tat and other strategies consistent with reciprocal altruism were sufficient to support cooperative outcomes. To this end, the chapter reviews the available archaeological and ethnographic evidence suggesting that most humans had frequent contact with a substantial number of individuals beyond the immediate family despite the existence of isolated groups. This conclusion is consistent with data on the extent of genetic differentiation among ethnographic foragers. The chapter then considers evidence that ancestral humans engaged in frequent and exceptionally lethal intergroup conflicts, as well as data implying that social order in prestate small-scale societies was sustained by a process of coordinated peer pressures and punishment. It shows that prehistoric human society was a social and natural environment in which group competition could have given rise to altruistic behaviors.

This chapter examines how group competition favored the coevolution of the distinctive institutions of the hunter-gatherer society along with a predisposition for altruistic behavior. It first considers how selective extinction can favor the evolution of an altruistic trait before discussing the notion of reproductive leveling, along with genetic differentiation between groups. It then discusses the link between deme extinction and the evolution of altruism; archaeological, ethnographic and genetic evidence from Australia; and the coevolution of institutions and altruism. It also presents the results of simulations on the gene-culture coevolution, showing that reproductive leveling and within-group segmentation could have coevolved with altruism.

This chapter examines the genetic structure of the Turks and Caicos iguana, Cyclura carinata carinata. It tests the assumption that overland dispersal does not limit gene flow among populations and attempts to determine if natural selection has played a role in shaping the current genetic structure of this species. It also assesses the relationship between geographic distance and genetic differentiation and how this relationship may have been affected by vicariance and dispersal. Finally, it considers the implications of the current genetic structure of Cyclura carinata carinata for future conservation initiatives.

This chapter discusses the genomic basis of ecological speciation. It empirically and theoretically explores the genomic perspective of speciation, leading to a more integrative understanding of ecological speciation. The main concept of this chapter is that genetic differentiation between populations is expected to be highly variable across the genome, possibly ranging from some regions with little or no differentiation through to fixed differences. It considers the expectations for genomic divergence at equilibrium and treats the transient effects of selective sweeps, both form new mutations and standing genetic variation. It also highlights key conceptual and theoretical points, and illustrates these points with empirical examples.

The number and geographic location of genetically differentiated populations must be identified to determine if fragmented populations require genetic management. Clustering of related genotypes to geographic locations (landscape genetic analyses) is used to determine the number of populations and their boundaries, with the simplest analyses relying on random mating within, but not across populations. Evidence of genetic differentiation among populations indicates either that they have drifted apart (and are likely inbred) and/or that the populations are adaptively differentiated. The current response when populations are genetically differentiated is usually to recommend separate management, but this is often ill-advised. A paradigm shift is needed where evidence of genetic differentiation among populations is followed by an assessment of whether populations are suffering genetic erosion, whether there are other populations to which they could be crossed, and whether the crosses would be beneficial, or harmful.

Chapter 3, “Quantifying genetic variation at the molecular level,” introduces quantitative methods for measuring variation directly in DNA sequences to help decipher fundamental properties of populations and what they can tell us about evolution. It provides an overview of the evolutionary factors that contribute to genetic variation, like mutational input, effective population size, genetic drift, migration rate, and models of migration. This chapter surveys the principal ways to measure and summarize polymorphisms within a single population and across multiple populations of a species, including heterozygosity, nucleotide polymorphism estimators of θ‎, the site frequency spectrum, and F_ST, and by providing illustrative natural examples. Populations are where evolution starts, after mutations arise as the spark of population genetic variation, and Chapter 3 describes how to quantify the variation to connect observations to predictions about how much polymorphism there ought to be under different circumstances.

Evidence of population structure and limited gene flow often leads to the questionable conclusion that populations should be managed as separate unit. A paradigm shift is needed where evidence of genetic differentiation among populations is followed by an assessment of whether populations are suffering genetic erosion, whether there are other populations to which they could be crossed, and whether the crosses would be beneficial, or harmful, and if beneficial, whether the benefits would be large enough to justify a genetic rescue attempt. Here we address these questions based on the principles established in the preceding chapters.

The theory of the evolution of phenotypic plasticity deals the role of the environment in determining the relationship between genotype and phenotype. The role of phenotypic plasticity in evolutionary processes was recognized as early as the 19th century, but did not rise to prominence until the 1980s. The chapter discussed the factors that promote and inhibit the evolution of adaptive phenotypic plasticity. For phenotypic plasticity to be favored by selection: (1) there must be a heterogeneous environment that affects the phenotypic expression of traits, (2) there must be spatial and/or temporal variation in the optimal phenotypic value of those plastic traits, (3) individuals or lineages must experience that environmental heterogeneity, and (4) those plastic traits must meet the other conditions required for evolution by natural selection. Three types of conditions can limit that evolution: (1) maintenance, production, or information-acquisition costs, (2) the lack of a reliable cue about the future state of the environment, and (3) developmental limitations. The chapter also examines the evolutionary consequences of phenotypic plasticity. The presence of phenotypic plasticity can act to either inhibit or enhance genetic differentiation, local adaptation, and species divergence. More information is needed on the prevalence of adaptive phenotypic plasticity.

Urbanisation impacts arthropod communities negatively but also creates opportunities for some species. Given their vital role in ecosystem function, arthropods are important components of urban landscapes, particularly in providing ecosystem services, including human well-being. The cityscape consists of a collection of habitat patches, ranging from fragmented natural habitats to characteristically urban habitats, such as parks, ruderal habitats, domestic gardens, roadside greens, and built surfaces, all of which have their own arthropod communities. Edge effects, patch size, and habitat quality interact with arthropod life history and morphological traits to structure arthropod communities in these island habitats. Research on the responses of arthropod communities along urban–rural gradients shows a general trend of a loss of specialist and poorly dispersive species at the urban end of the gradient. This chapter recommends moving beyond such pattern-driven research, with a new focus on quantifying the concepts of disturbance and urbanisation to unravel the processes that generate species responses to urbanisation. Despite negative effects of urban development, these environments also select for life history, morphological and physiological changes, and ultimately for genetic differentiation in arthropod populations. However, there is still much to be learnt about how urbanisation structures the population genetics of arthropod populations. The task of conserving urban arthropod biodiversity is challenging, not least because many adults do not like bugs. However, through education and conservation projects in urban areas, such fears can be alleviated. Collaboration among landscape architects, urban ecologists, and entomologists can help to meet biodiversity objectives in urban areas and this will have ecological and social benefits.