Does natural selection act primarily on individual organisms, on groups, on genes, or on whole species? Samir Okasha provides a comprehensive analysis of the debate in evolutionary biology over the levels of selection, focusing on conceptual, philosophical and foundational questions. A systematic framework is developed for thinking about natural selection acting at multiple levels of the biological hierarchy; the framework is then used to help resolve outstanding issues. Considerable attention is paid to the concept of causality as it relates to the levels of selection, in particular the idea that natural selection at one hierarchical level can have effects that 'filter' up or down to other levels. Unlike previous work in this area by philosophers of science, full account is taken of the recent biological literature on 'major evolutionary transitions' and the recent resurgence of interest in multi-level selection theory among biologists. Other biological topics discussed include Price's equation, kin and group selection, the gene's eye view, evolutionary game theory, outlaws and selfish genetic elements, species and clade selection, and the evolution of individuality. Philosophical topics discussed include reductionism and holism, causation and correlation, the nature of hierarchical organization, and realism and pluralism.

Evolutionary biologists have recognised that natural selection operates for the good of lower-level units (the individual, the cell, even the gene) rather than the good of the group. In this volume, 12 scientists discuss why this should be the case.

Does natural selection act primarily on individual organisms, on groups, on genes, or on whole species? This book provides a comprehensive analysis of the debate in evolutionary biology over the levels of selection, focusing on conceptual, philosophical and foundational questions.

Much of the evolutionary debate since Darwin has focused on the level at which natural selection occurs. Most biologists acknowledge multiple levels of selection—from the gene to the species. The debate about group selection, however, is the focus of Mark E. Borrello’s Evolutionary Restraints. Tracing the history of biological attempts to determine whether selection leads to the evolution of fitter groups, Borrello takes as his focus the British naturalist V. C. Wynne-Edwards, who proposed that animals could regulate their own populations and thus avoid overexploitation of their resources. By the mid-twentieth century, Wynne-Edwards became an advocate for group selection theory and led a debate that engaged the most significant evolutionary biologists of his time, including Ernst Mayr, G. C. Williams, and Richard Dawkins. This important dialogue bled out into broader conversations about population regulation, environmental crises, and the evolution of human social behavior. By examining a single facet in the long debate about evolution, Borrello provides powerful insight into an intellectual quandary that remains relevant and alive to this day.

Biological evolution is a fact—but the many conflicting theories of evolution remain controversial even today. When Adaptation and Natural Selection was first published in 1966, it struck a powerful blow against those who argued for the concept of group selection—the idea that evolution acts to select entire species rather than individuals. Williams’s famous work in favor of simple Darwinism over group selection has become a classic of science literature, valued for its thorough and convincing argument and its relevance to many fields outside of biology. Now with a new foreword by Richard Dawkins, Adaptation and Natural Selection is an essential text for understanding the nature of scientific debate.

In this work, George C. Williams--one of evolutionary biology's most distinguished scholars--examines the mechanisms and meaning of natural selection in evolution. Williams offers his own perspective on modern evolutionary theory, including discussions of the gene as the unit of selection, clade selection and macroevolution, diversity within and among populations, stasis, and other timely and provocative topics. In dealing with the levels-of-selection controversy, he urges a pervasive form of the replicator-vehicle distinction. Natural selection, he argues, takes place in the separate domains of information and matter. Levels-of-selection questions, consequently, require different theoretical devices depending on the domains being discussed. In addressing these topics, Williams presents a synthesis of his three decades of research and creative thought which have contributed greatly to evolutionary biology in this century.

Debates concerning the units and levels of selection have persisted for over fifty years. One major question in this literature is whether units and levels of selection are genuine, in the sense that they are objective features of the world, or merely reflect the interests and goals of an observer. Scientists and philosophers have proposed a range of answers to this question. This Element introduces this literature and proposes a novel contribution. It defends a realist stance and offers a way of delineating genuine levels of selection by invoking the notion of a functional unit.