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This chapter studies the logic of evolution by natural selection and the origin of the levels of selection question. The abstract nature of the core Darwinian principles, and thus their potential applicability at multiple levels of the biological hierarchy, is emphasized. Price's equation — a key foundational result in evolutionary theory — is introduced and discussed, which teaches us that character-fitness covariance is the essence of natural selection. The relation between Price's equation and Lewontin's tripartite analysis of the conditions required for Darwinian evolution is briefly examined.

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.

Artificial selection provides a means of validating evolutionary principles, and is the basis of applied evolutionary biology. This chapter describes both short-term and long-term responses to selection for defined phenotypic characteristics. The first section of this chapter, Selection acting on quantitative variation, describes inheritance of quantitative characters; stabilizing selection; directional selection of quantitative characters; and stabilizing selection of quantitative characters. The second section is called Generations 1-10, the short-term response, and talks about a bristle experiment; the short-term response; asymmetry; divergence; selection of heritable merit; the indirect response to selection; the tertiary theorem of natural selection; and stabilizing selection. The next section called Generations 10-100, the limits to selection, discusses surpassing the ancestor; the selection limit; heroic experiments; the limits to selection in terms of loss of useful variation; long-continued response in terms of recurrent mutation; long-continued response in terms of environmental variance; limits to selection in terms of countervailing natural selection; the limits to stabilizing selection; and transcending the limit. Finally, the section entitled Generations 100 up - new kinds of creatures, discusses selection for yield in crop plants; historical improvement; and domestication.

Natural selection can be observed and measured in natural populations. This chapter argues that it is commonplace, strong, fluctuating, and oligogenic. The first section here is called Fitness in natural populations and describes the variance of fitness; immigration pressure; local selection coefficients; and the field gradient. The next section, the Phenotypic selection, details the environmental variance of fitness; the cost of selection; the lack of response: genostasis; field studies of selection in Cepaea; selection coefficients; heritability; the Secondary Theorem of Natural Selection; selection gradients; stabilizing selection; fluctuating selection; historical change; multiscale temporal variation; and genetic revolutions. The third section is called Selection experiments in the field and details habitat modification and the Rothamsted Park Grass Experiment. It then gives an introduction to guppies in Trinidad. The fourth section is called Adaptation to the humanized landscape and details the unexpected consequences of harvesting; the unintended consequences of pollution in terms of mining; the unintended consequences of pollution from smoke; the unintended consequences of pollution from carbon dioxide; the unwelcome effects of eradication concerning herbicides and pesticide; the unwelcome consequences of eradication from antibiotics; and human evolution in the humanized environment. Finally, the section called The ghost of selection past details an analysis of allele frequencies and an analysis of divergence.

This chapter examines which of the equivalent alternative partitions of fitness, including inclusive fitness and group fitness, can be interpreted as being subject to natural selection in a meaningful way. Inclusive fitness theory can deal with subtleties such as nonadditive fitness effects and conditionally expressed phenotypes. However, selection based on inclusive fitness gives equivalent predictions to other models of apparently different evolutionary processes, such as multilevel selection. The chapter considers how we can determine whether inclusive fitness really captures the essence of social evolution and whether inclusive fitness is really maximized by the action of selection, as suggested by William D. Hamilton. It also explains what heritability measures, and whether this makes sense biologically. Finally, it discusses the problem of classifying observed social behaviors in terms of their underlying evolutionary explanations.

This chapter focuses on the methodological issues arising from the discrepancy between the results of heritability studies and epidemiologic designs. It focuses on the basic principles of the heritability design. The discussion is limited to heritability studies of twins, which is used as a prototype. The discussion is also limited to a categorical disease outcome. The chapter begins by describing the twin study, a type of natural experiment, and explains how it can estimate the contributions of genetic and environmental causes of a disorder. It then compares the twin studies to risk factor designs. It proposes a reason that these approaches can yield different results for the effect of shared family environment.

This chapter provides an overview of basic principles of coevolutionary biology, including both microevolutionary (ecological) and macroevolutionary (historical) approaches and their integration. It defines the main terminology used in coevolutionary biology. It discusses the relationship between coadaptation, codiversification, and coevolution. The chapter considers the relationship of reciprocal phenotypic selection to coadaptive responses of heritable traits. It introduces the geographic mosaic theory of coevolution and considers the central roles of dispersal and population structure, as well as GxGxE interactions. Chapter 1 briefly reviews the fossil evidence for coevolution. It introduces co-phylogenetic approaches and the cospeciation - host-switching continuum. The chapter concludes by considering why permanent parasites are unusually tractable model systems for studies of coevolution, and by introducing the concept of “ecological replicates.”

This chapter introduces statistical methods for twin and sibling studies using random effects models. The classic twin study begins from assessing the variance of a trait (called a phenotype by geneticists) in a large group, and attempts to estimate how much of this is due to genetic effects (heritability), how much appears to be due to shared environmental effects, and how much is due to unique environmental effects — events occurring to one twin but not another. This chapter shows how three families of random effect models, random effects models for normally distributed traits, generalized linear mixed models for binary and count data, and frailty models for survival data may be used for modelling variances in longitudinal, or life course setting. The methods are illustrated using data from The Swedish Adoption/Twin Study of Aging. The appendix provides the R and Winbugs codes that are used in the analyses.

Sewall Wright originally conceived of his Adaptive Landscape as a visual device to capture the consequences of non-linear (epistatic) interactions between genes. A useful way to visualise a multivariate non-linear function is through a ‘landscape’, an important factor to consider when applying Adaptive Landscape models to questions about the evolution of development. This chapter examines how a phenotype landscape (also known as phenotypic landscape or developmental landscape) can explicitly map genetic and developmental traits to the phenotypic traits upon which selection acts. After outlining the basic properties of phenotype landscapes, it considers how they are used in concert with an Adaptive Landscape to study the evolution of development. It then describes the formal theory for evolution on phenotype landscapes and how it generalises the quantitative genetic approaches that are often applied to Adaptive Landscapes. The chapter concludes by illustrating how phenotype landscape theory can be used to study the evolution of genetic covariance, heritability, and novelty.

Genetic determinants of ageing have the potential to inform us about a wide range of molecular pathways which are not yet understood and which may offer the potential for modification. This chapter addresses heritability studies to genome-wide molecular studies of complex traits related to ageing. Ageing research in model organisms is described, which has motivated genetics of ageing research in humans. It has been much easier to study ageing and longevity in mice, flies, and worms than it is to determine genetic processes of ageing in man. This is because researchers have been able to breed these species in controlled experiments to identify strains exhibiting longer lives or specific characteristics. The short life cycles and greater ease of characterizing specific genes involved, has given insight into some important ageing pathways. Topics such as disease and ageing and the future of research into ageing genetics are also touched upon.

Because of their dynamic and heritable properties, epigenetic mechanisms have emerged as a promising biological explanation linking events and exposures across life to long-term health. Epigenetics also provides a useful conceptual model on which to base intervention strategies to improve healthy ageing. Epigenetic mechanisms involve the modification of DNA in ways that influence structure and function. Epigenotype is influenced by genotype but unlike genotype there is the potential for modification. Epigenetic states have been implicated in a wide range of diseases though the mechanisms are not fully understood. There is evidence for nutritional and behavioural programming of epigenetic states, with early life and the period before birth being particularly important. There is some evidence that epigenetic states resulting from adverse events/exposures at earlier life stages may be reversible. Epigenetic states have the potential to provide markers of biological age and objective markers of complex exposures in life course studies.

Phenotypic plasticity is the property of a genotype to produce different phenotypes in response to different environmental conditions (Bradshaw 1965; Mazer and Damuth, this volume, chapter 2). Simply put, students of phenotypic plasticity deal with the way nature (genes) and nurture (environment) interact to yield the anatomy, morphology, and behavior of living organisms. Of course, not all genotypes respond differentially to changes in the environment, and not all environmental changes elicit a different phenotype given a particular genotype. Furthermore, while the distinction between genotype and phenotype is in principle very clear, several complicating factors immediately ensue. For example, the genotype can be modified by environmental action, as in the case of DNA methylation patterns (e.g., Sano et al. 1990; Mazer and Damuth, this volume, chapter 2). More intuitively, since environments are constantly changed by the organisms that live in them, the genetic constitution of a population influences the environment itself. Perhaps the most intuitive way to visualize phenotypic plasticity is through what is termed a norm of reaction. This genotype-specific function relates the phenotypes produced to the environments in which they are produced. The figure presents a simple example with a population made of three different genotypes experiencing a series of environmental conditions. Genotype 1 yields a low phenotypic value toward the left end of the environmental continuum (say, an insect with small wings at low temperature) but a high phenotypic value at the opposite environmental extreme (say, large wings at high temperature). Genotype 3, however, does the exact opposite, while genotype 2 is unresponsive to environmental changes, always producing the same phenotype regardless of the conditions (within the range of environments considered). Even though the case presented in figure 5.1 is very simple (notice, for example, that the reaction norms are linear, which is unlikely in real situations), several general principles are readily understood following a closer analysis: … 1. Let us consider the relationship between phenotypic plasticity and reaction norms. While the two terms are often used as synonyms, they are clearly not. A reaction norm is the trajectory in environment-phenotype space that is typical of a given genotype; plasticity is the degree to which that reaction norm deviates from a flat line parallel to the environmental axis. …

During the last few decades, family, twin, and adoption designs have been used to assess the genetic and environmental etiologies of specific cognitive abilities (SCA). The largest family study of SCA was the Hawaii Family Study of Cognition, which included test data from 1,816 intact nuclear families. Measures of parent-offspring resemblance can only be considered via upper-bound estimates of heritability. Thus, family studies can provide conclusive evidence for the familiarity of a trait, but not for its genetic etiology. In contrast, results obtained from twin studies can provide estimates of heritability. This chapter discusses the results of multivariate genetic analyses of Colorado Adoption Project (CAP) parent-offspring data at seven and twelve years of age, and compares them to those obtained by Rice et al. (1989) when the CAP children were only four years of age. The etiologies of individual differences for each of the four measures — verbal, spatial, perceptual speed, and memory — and their covariation were assessed by fitting a parent-offspring multivariate conditional path model to CAP specific cognitive abilities data.

This chapter explores memory ability in the Colorado Adoption Project (CAP) at ages nine, ten, twelve, and fourteen. Although memory has been examined longitudinally in conjunction with other cognitive abilities, this chapter examines memory ability in CAP more systematically using isomorphic tests measured during the transition from middle childhood to adolescence. Given that heritability of memory may vary by the type of memory measure employed, the chapter first analyzes different aspects of memory through both phenotypic and univariate genetic analyses before exploring their longitudinal relationships. It is hypothesized in this chapter that like other cognitive abilities such as verbal ability, spatial ability, and perceptual speed, genes will be largely responsible for the similarity in memory across time while the non-shared environment will be largely responsible for the discrepancy between longitudinally assessed memory scores. The results show that the correlation between memory tests was driven almost completely by shared genetic factors while the discrepancy between memory tasks was influenced largely by the non-shared environment (and error).

Attention problems are highly prevalent, with rates of occurrence depending on the definition used, and make up to 50% of child psychiatric cases. Previous behavior genetic studies of attention problems have analyzed either twin, family, or adoption data, and reported heritability estimates ranging from 0.55 to 0.98. Adoption studies can provide a direct test for the presence of shared environmental factors by examining the similarity between unrelated siblings growing up in the same family; however, the power will be relatively low in small samples. Previous studies reported that adoptees show an increased incidence of attention problems, as high as 13–21% in some samples. This chapter discusses the results of a study showing that both mothers and teachers rate boys as having more attention problems. Separating the overall score into the aspects of inattention and hyperactivity follows the overall picture in that boys seem to show more of these behaviors than girls. For both sexes, the behaviors were rated as relatively stable during the grade-school years.

This chapter concentrates primarily on the period up to 1135, with the balance of evidence causing some prioritisation of the reign of Henry I. It begins with the issue of lordship and lay landholding, and then examines the questions of security of tenure, heritability, and alienability. Information is most extensive for the upper levels of society, and the potential for variation according to social standing must be remembered. The divisions between forms of tenure apparent in later mediaeval common law — frankalmoign, knight service, serjeanty, socage, and villeinage — are only to a limited and varying degree apparent in the Anglo-Norman period. Analysis here is divided into the following general categories; lay free landholding; lay unfree landholding; and ecclesiastical landholding.

In this chapter, the efficacy of group selection and the debates over it role, if any, in natural populations is discussed from the perspective of two different contexts. One debate is centered on the existence of group adaptations. Individuals are deconstructed into their component adaptations and, for each such trait, the question is asked, “Who benefits?” If a trait benefits individuals, then it evolved as an adaptation for individuals by individual selection. If it is a trait that benefits groups, then it evolved as an adaptation for groups by group selection. The second debate is based in evolutionary genetics and multilevel selection with its roots in quantitative genetics and animal breeding. The genetic basis of a response to individual or group selection is important to one context but not to the other.

In this chapter, the theoretical relationship between the strength of random genetic drift and the rate of increase of group heritability is discussed. The experimental methods for estimating effective population size and the effective migration rate among Tribolium demes in the laboratory are outlined and diagrammed. The author discusses the distinction between genetic variability and heritability at the group level. A discussion of the results of experiments introducing migration at different levels and in different patterns among demes; random drift of population mean fitness for different numbers of founding adults; and the relationship between estimated and realized group heritability.