Search Results

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.

This chapter traces the history of metapopulation studies from the introduction of the term by Levins in 1970 to its investigation in a variety of field, theoretical and laboratory systems. The prerequisites for group selection in a metapopulation and how genetic interactions affect selection within and among groups of individuals are discussed. The metaphor of the card games war and poker is introduced to illustrate how the meaning of gene effect is changed by interactions.

The theory that organisms become adapted to their environment through the process of natural selection has become so ingrained in modern biological thought, and more generally in Western culture of the late 20th century, that it is surely one of the great scientific paradigms of the present era. Evolution and adaptation were both well-accepted concepts by the mid-19th century, at least among French and British natural philosophers. The theory of natural selection, developed by Wallace (1858) and Darwin (1859), provided a functional connection between the two processes. However, despite its logical consistency, natural selection was not accepted as a necessary or sufficient explanation for adaptation until the “evolutionary synthesis” of the mid-20th century, when knowledge from population and quantitative genetics, natural history (e.g., biogeography, ecology, behavior), systematics, and paleontology merged to form the unified theory of adaptive evolution known as neo-Darwinism (see Futuyma 1998 for a concise review of this history). Since that time, natural selection has been accepted as the universal mechanism leading to adaptation, and the two terms have become so closely associated as to be almost tautological. Adaptationist hypotheses are now fundamental to much of modern biology and are becoming increasingly apparent in more disparate fields, such as anthropology, medicine, biochemistry, and psychology (Futuyma 1999). Nevertheless, there is much that natural selection cannot explain. For example, chance events may strongly influence macroevolutionary trends (i.e., the origin and extinction of species and higher taxa), some aspects of molecular evolution, and evolution within small or subdivided populations (Mazer and Damuth, this volume, chapter 2; Nunny, this volume). For this reason, adaptationist hypotheses should be viewed with skepticism until adequately tested (Reznick and Travis, this volume). In this chapter, we carefully define natural selection and discuss methods of measuring selection in natural populations as a means of testing adaptationist hypotheses. These methods are most appropriate for testing hypotheses concerning the adaptive significance of contemporary trait distributions within and among populations (“microevolutionary” hypotheses) and thus have particular relevance for evolutionary ecologists. Readers will find many additional examples of these and other methods of testing microevolutionary adaptationist hypotheses throughout this volume, such tests being an essential component of most research programs in evolutionary ecology.

The expected response in the mean of a trait subjected to a single generation of selection from an unselected base population is usually well-approximated by the breeder's equation, R = h²S. This chapter shows how this basic equation generalizes to an important number of settings, such as differential selection on the two sexes, overlapping generations, and selection based on measures other than just an individual's phenotype. It also briefly examines selection response on multiple traits.

This chapter contains a discussion of the ecological and the genetic basis for Sewall Wright’s Shifting Balance Theory. It also relays discussions of the author with Wright about how to experimentally test his theory using flour beetle metapopulations. The experimental design used by Wade and C. J. Goodnight to test Wright’s theory and to estimate realized group heritabilities is illustrated. The surprizing finding that interdemic selection every-other generation produced a larger response than selection at every generation was interpreted as evidence of non-additive effects on population mean fitness.

This chapter contributes to the explanation to how environmental migrants are ‘selected’ at the individual and small group level. It argues that individual decisions to migrate depend on the type of environmental change. The author distinguishes between sudden onset environmental problems (e.g. natural disasters) and slow onset environmental problems (e.g. climate change). Sudden onsets make push factors more important- They give migrants less power over their decision to migrate, and therefore include more vulnerable population groups. On the contrary, slow onset events create opportunities for individual agency. Governance can play an important role as it can influence migration and environmental change, especially on the local and state level. The author argues that democratic governance arrangements confer agency to individuals and non-democratic governance delimits it. Moreover, the management of sudden onsets in the short run can be more effective in non-democratic governance, while slow onset environmental changes call for democratic governance arrangements.