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Individual development unfolds through a dynamic interplay of regulatory elements, including environmental inputs. This chapter provides a general overview of the mechanisms currently understood to regulate gene expression, including transcription factors and other genetic interactions, alternative splicing and editing of coding sequences, epigenetic methylation and histone modifications, and noncoding RNAs. A key point is that “normal” development is influenced by environmental as well as molecular factors. The chapter argues for a unified ecological development approach that explicitly studies both expression mechanisms and phenotypic outcomes in environmental context. Central to this eco-devo approach is the norm of reaction, the set of phenotypes that a genotype produces in response to specific conditions. A discussion of genotype × environment (G × E) interaction draws on recent examples. In this unified approach to development, plasticity and canalization describe different response patterns but not distinct biological mechanisms. Finally, experimental design issues are briefly addressed.

Selection arises from the encounter between phenotypes, which are environmentally influenced, and environments, which in turn are modified by the organisms themselves. This chapter examines selective evolution in the context of these reciprocal effects. First, new insights into phenotypic variation and heredity are summarized to expand a strictly allelic evolutionary model. A key point is that immediate as well as inherited environmental influences affect fitness variation and, consequently, play an evolutionary role. A section on the evolution of reaction norms explains environmentally contingent patterns of genetic variance (G × E interaction and cryptic variation) and argues that plasticity can buffer selective impact, facilitate evolutionary divergence, or both. The impact of heritable epigenetic factors on selective dynamics is then discussed. A section on selective feedbacks due to niche construction (eco-evolutionary feedbacks) provides case studies and reviews theoretical insights, including coevolutionary implications. A final section considers how reciprocal organism–environment effects can be integrated to inform studies of adaptation and selection.

Altruism has many meanings both in science and in common language. In multilevel selection theory, “increase” and “decrease” are defined in relative terms. If an individual increases the fitness of its group, relative to other groups, while decreasing its own fitness, relative to other individuals in the same group, then it qualifies as an evolutionary altruist. In evolutionary jargon, phenotypically plastic is termed as “norm of reaction,” and it is portrayed graphically by showing the different environments on the x-axis and the corresponding phenotypes on the y-axis. To characterize a phenotypically plastic organism, we must know its repertoire of responses.

Evolutionary psychologists' thinking about stability and change in human cognition and behavior has been shaped by two bad metaphors: the "blank slate" and "hard-wired" human nature. These metaphors can be corrected by examining the underlying conceptions of internal and external causes of change, and of how these interact to enable organisms to be robust to some environmental changes by actively responding to others.

The field of evolutionary ecology is at its core the study of variation within individuals, among individuals, among populations, and among species. For several reasons, evolutionary ecologists need to know the causes and the effects of variation in traits that influence the performance, behavior, longevity, and fertility of individuals in their natural habitats. First, to determine whether the conditions for evolution by natural selection of traits of interest are fulfilled, we need to know the degree to which the phenotype of a trait is determined by the genetic constitution (or genotype) of an individual and by the environment in which an individual is raised. Second, to predict whether and how natural selection will cause the mean phenotype of a trait in a population to change from one generation to the next, we must understand the ways in which an individual’s phenotype (for this trait) influences its genetic contribution to future generations (i.e., its fitness). Third, to understand why the phenotype of a given trait influences an individual’s fitness, we need to know how the trait affects an individual’s ability to garner resources for growth or reproduction, to avoid predation, to find mates, and to reproduce successfully. Finally, to evaluate whether the phenotypic differences we observe among populations and species may represent the long-term outcome of evolution by natural selection, we must understand how different phenotypes perform under different environmental conditions. In sum, with an understanding of the causes and consequences of phenotypic variation within and among populations, we can detect evolutionary processes operating at a variety of ecological levels: within random-mating populations; within and among subpopulations distributed over a species’ geographic range; and even among multispecies associations. These goals, however, require a clear understanding of the nature of phenotypic variation. The aim of this chapter and the next is to illustrate that the richness of evolutionary ecology has increased in direct proportion to our understanding of the multiple causes of intraspecific phenotypic variation.