Units and levels of selection

Author(s):  
Samir Okasha

In a standard Darwinian explanation, natural selection takes place at the level of the individual organism, i.e. some organisms enjoy a survival or reproduction advantage over others, which results in evolutionary change. In principle however, natural selection could operate at other hierarchical levels too, above and below that of the organism, for example the level of genes, cells, groups, colonies or even whole species. This possibility gives rise to the ‘levels of selection’ question in evolutionary biology. Group and colony-level selection have been proposed, originally by Darwin, as a means by which altruism can evolve. (In biology, ‘altruism’ refers to behaviour which entails a fitness cost to the individual so behaving, but benefits others.) Though this idea is still alive today, many theorists regard kin selection as a superior explanation for the existence of altruism. Kin selection arises from the fact that relatives share genes, so if an organism behaves altruistically towards its relatives, there is a greater than random chance that the beneficiary of the altruistic action will itself be an altruist. Kin selection is closely bound up with the ‘gene’s eye view’ of evolution, which holds that genes, not organisms, are the true beneficiaries of the evolutionary process. The gene’s eye approach to evolution, though heuristically valuable, does not in itself resolve the levels of selection question, because selection processes that occur at many hierarchical levels can all be seen from a gene’s eye viewpoint. In recent years, the levels of selection discussion has been re-invigorated, and subtly transformed, by the important new work on the ‘major evolutionary transitions’. These transitions occur when a number of free-living biological units, originally capable of surviving and reproducing alone, become integrated into a larger whole, giving rise to a new biological unit at a higher level of organization. Evolutionary transitions are intimately bound up with the levels of selection issue, because during a transition the potential exists for selection to operate simultaneously at two different hierarchical levels.

Author(s):  
Samir Okasha

‘Levels of selection’ examines the levels-of-selection question, which asks whether natural selection acts on individuals, genes, or groups. This question is one of the most fundamental in evolutionary biology, and the subject of much controversy. Traditionally, biologists have mostly been concerned with selection and adaptation at the individual level. But, in theory, there are other possibilities, including selection on sub-individual units such as genes and cells, and on supra-individual units such as groups and colonies. Group selection, altruistic behaviour, kin selection, the gene-centric view of evolution, and the major transitions in evolution are all discussed.


2017 ◽  
Vol 4 (10) ◽  
pp. 170470 ◽  
Author(s):  
Marta Bertolaso ◽  
Anna Maria Dieli

The major transitions approach in evolutionary biology has shown that the intercellular cooperation that characterizes multicellular organisms would never have emerged without some kind of multilevel selection. Relying on this view, the Evolutionary Somatic view of cancer considers cancer as a breakdown of intercellular cooperation and as a loss of the balance between selection processes that take place at different levels of organization (particularly single cell and individual organism). This seems an elegant unifying framework for healthy organism, carcinogenesis, tumour proliferation, metastasis and other phenomena such as ageing. However, the gene-centric version of Darwinian evolution, which is often adopted in cancer research, runs into empirical problems: proto-tumoural and tumoural features in precancerous cells that would undergo ‘natural selection’ have proved hard to demonstrate; cells are radically context-dependent, and some stages of cancer are poorly related to genetic change. Recent perspectives propose that breakdown of intercellular cooperation could depend on ‘fields’ and other higher-level phenomena, and could be even mutations independent. Indeed, the field would be the context, allowing (or preventing) genetic mutations to undergo an intra-organism process analogous to natural selection. The complexities surrounding somatic evolution call for integration between multiple incomplete frameworks for interpreting intercellular cooperation and its pathologies.


1993 ◽  
Vol 1 (1_2) ◽  
pp. 179-209 ◽  
Author(s):  
Thomas S. Ray

Our concepts of biology, evolution, and complexity are constrained by having observed only a single instance of life, life on earth. A truly comparative biology is needed to extend these concepts. Because we cannot observe life on other planets, we are left with the alternative of creating Artificial Life forms on earth. I will discuss the approach of inoculating evolution by natural selection into the medium of the digital computer. This is not a physical/chemical medium; it is a logical/informational medium. Thus, these new instances of evolution are not subject to the same physical laws as organic evolution (e.g., the laws of thermodynamics) and exist in what amounts to another universe, governed by the “physical laws” of the logic of the computer. This exercise gives us a broader perspective on what evolution is and what it does. An evolutionary approach to synthetic biology consists of inoculating the process of evolution by natural selection into an artificial medium. Evolution is then allowed to find the natural forms of living organisms in the artificial medium. These are not models of life, but independent instances of life. This essay is intended to communicate a way of thinking about synthetic biology that leads to a particular approach: to understand and respect the natural form of the artificial medium, to facilitate the process of evolution in generating forms that are adapted to the medium, and to let evolution find forms and processes that naturally exploit the possibilities inherent in the medium. Examples are cited of synthetic biology embedded in the computational medium, where in addition to being an exercise in experimental comparative evolutionary biology, it is also a possible means of harnessing the evolutionary process for the production of complex computer software.


2018 ◽  
Author(s):  
Mikhail I. Katsnelson ◽  
Yuri I. Wolf ◽  
Eugene V. Koonin

One of the key tenets of Darwin’s theory that was inherited by the Modern Synthesis of evolutionary biology is gradualism, that is, the notion that evolution proceeds gradually, via accumulation of “infinitesimally small” heritable changes 1,2. However, some of the most consequential evolutionary changes, such as, for example, the emergence of major taxa, seem to occur abruptly rather than gradually, as captured in the concepts of punctuated equilibrium 3,4 and evolutionary transitions 5,6. We examine a mathematical model of an evolutionary process on a rugged fitness landscape 7,8 and obtain analytic solutions for the probability of multi-mutational leaps, that is, several mutations occurring simultaneously, within a single generation in one genome, and being fixed all together in the evolving population. The results indicate that, for typical, empirically observed combinations of the parameters of the evolutionary process, namely, effective population size, mutation rate, and distribution of selection coefficients of mutations, the probability of a multi-mutational leap is low, and accordingly, their contribution to the evolutionary process is minor at best. However, such leaps could become an important factor of evolution in situations of population bottlenecks and elevated mutation rates, such as stress-induced mutagenesis in microbes or tumor progression, as well as major evolutionary transitions and evolution of primordial replicators.


2021 ◽  
Vol 9 ◽  
Author(s):  
Christoph Thies ◽  
Richard A. Watson

Kin selection theory and multilevel selection theory are distinct approaches to explaining the evolution of social traits. The latter claims that it is useful to regard selection as a process that can occur on multiple levels of organisation such as the level of individuals and the level of groups. This is reflected in a decomposition of fitness into an individual component and a group component. This multilevel view is central to understanding and characterising evolutionary transitions in individuality, e.g., from unicellular life to multicellular organisms, but currently suffers from the lack of a consistent, quantifiable measure. Specifically, the two major statistical tools to determine the coefficients of such a decomposition, the multilevel Price equation and contextual analysis, are inconsistent and may disagree on whether group selection is present. Here we show that the reason for the discrepancies is that underlying the multilevel Price equation and contextual analysis are two non-equivalent causal models for the generation of individual fitness effects (thus leaving different “remainders” explained by group effects). While the multilevel Price equation assumes that the individual effect of a trait determines an individual's relative success within a group, contextual analysis posits that the individual effect is context-independent. Since these different assumptions reflect claims about the causal structure of the system, the correct approach cannot be determined on general theoretical or statistical grounds but must be identified by experimental intervention. We outline interventions that reveal the underlying causal structure and thus facilitate choosing the appropriate approach. We note that kin selection theory with its focus on the individual is immune to such inconsistency because it does not address causal structure with respect to levels of organisation. In contrast, our analysis of the two approaches to measuring group selection demonstrates that multilevel selection theory adds meaningful (falsifiable) causal structure to explain the sources of individual fitness and thereby constitutes a proper refinement of kin selection theory. Taking such refined causal structure into account seems indispensable for studying evolutionary transitions in individuality because these transitions are characterised by changes in the selection pressures that act on the respective levels.


2021 ◽  
pp. 151-179
Author(s):  
J. Arvid Ågren

The initial success of the gene’s-eye view came from making sense of old problems in evolutionary biology, in particular those related to social behaviour. It also stimulated new empirical research areas. This chapter is about three such new areas. The first is extended phenotypes, which are examples of phenotypic effects that occur outside of the body in which a gene is located. The second area is greenbeard genes, which gets its name from the thought-experiment devised to show that for altruism to evolve it is the relatedness between the actor and the recipient at the locus underlying the altruistic behaviour that matters, not the genome-wide relatedness. Finally, selfish genetic elements are genetic elements that have the ability to promote their own transmission even if it come at the expense of the fitness of the individual organism. The chapter outlines the current understanding of these topics and the role of the gene’s-eye view in uncovering them.


Author(s):  
Keith Stewart Thomson

J. Maynard Smith (1983) has written that “although we have a clear and highly articulated theory of evolution, we have no comparable theory of development.” I would turn this statement around somewhat and say that until we have a general theory of development we are unlikely to be able to derive a complete theory of evolution. This does not mean that a theory of evolution is wholly contained, in some reductionist sense (see Chapter 2), within a theory of development. However, if developmental processes play a major role in determining the modes and tempi of introduction of new variation at the level of the individual organism, and if they also have roles in upward and downward causation to other focal levels in the hierarchy of evolutionary mechanisms, then at least some of the rules of variation must be contained within the rules of development. If we are to progress in evolutionary biology beyond the study only of the contingent, and of unique empirical events, we will need a general theory, and part of that theory must derive from theories of the developmental processes that drive the introduction of variation. From developmental theory we will be able to make new general statements about how variation can be introduced at the phenotypic level. Although we still lack any such general theory, we can begin the process by using the preceding discussions at least to propose some general properties of developmental systems. The properties and processes of morphogenesis form an extremely complex system. Perhaps the hardest parts to grapple with are those “whole-organism” properties by which any given region of the developing embryo responds to field phenomena created by and expressed within the organism as a single whole rather than as a collection of isolated units, each with their own independent problems, mechanisms, and histories. Although these are vital questions (no pun intended), relatively little experimental work is being conducted in this area for obvious conceptual and technical reasons. Reductionist, functionalist approaches tend to make one concentrate on the parts rather than the whole.


2021 ◽  
pp. 119-130
Author(s):  
Franklin M. Harold

Why are there so many kinds of organisms, and why do they cluster into discrete groups associated with particular locales? These and other ecological questions find answers in the expansive version of evolution that is presently emerging. Heredity, variation, natural selection, and adaptation are rooted in the level of genes, but incorporate features that grow out of the many tiers of biological organization. The communitarian view of life complements the one focused on the individual organism, and requires us to reexamine the meaning of both organism and individual. It embraces broad-gauge phenomena such as nutrient cycles, and gave birth to Gaia: the vision of Earth as a self-regulating system that has kept our planet hospitable to life for nearly 4 billion years.


Author(s):  
Martin Fichman

Alfred Russel Wallace (b. 1823–d. 1913) was one of the most brilliant theoretical and field biologists of the 19th century. He was a meticulous field observer, a prolific generator of ideas on a broad spectrum of issues ranging from evolutionary biology to social and political concerns, and a theoretician whose work laid some of the main foundations for the scientific study of biogeography and evolution. Wallace undertook two tropical journeys that were to transform his life and the emerging science of evolutionary biology: a four-year exploration of the Amazon basin of South America (1848–1852) and an eight-year exploration of the Malay Archipelago (1854–1862), including the islands of Java, Borneo, Celebes, New Guinea, and Bali. Wallace later generalized his findings from Southeast Asia to elaborate a global paradigm for identifying the earth’s fundamental biogeographical regions in his magisterial Geographical Distribution of Animals (1876). It was, of course, Wallace’s elucidation of the mechanism of evolution—in his 1858 “On the Tendency of Varieties to Depart Indefinitely from the Original Type”—that constitutes his greatest scientific legacy from his Malay travels. A copy of Wallace’s essay, along with extracts from an unpublished manuscript on natural selection written by Darwin in 1844, were presented together at the historic meeting of the Linnean Society (London) on 1 July 1858. This meeting—a year prior to the publication of Darwin’s On the origin of species (1859)—ensured that both Wallace and Darwin received recognition and joint priority for their momentous discovery of natural selection. Wallace spent the remainder of his long life in elucidating the implications of evolutionary theory for biogeography, sexual selection, the phenomenon of organic mimicry taxonomy, physical geography and geology, and anthropology. Although he remained an ardent selectionist in his overall analysis of evolutionary processes, Wallace considered natural selection inadequate to account completely for the origin and development of certain human characteristics, notably, consciousness and the moral sense. He insisted that certain aspects of theism and of political and social ideologies, including socialism, spiritualism, and anti-vaccinationism, were not merely compatible with the evolutionary process but essential for comprehending the full significance of human evolution. The issues Wallace confronted continue to resonate in contemporary debates on the scope, mechanism, and, ultimately, significance of evolution in both scientific and cultural domains. In the past two decades there has been a resurgence of interest in Wallace, and this article provides a scholarly guide through the thicket of materials now emerging on his life and achievements.


2015 ◽  
Author(s):  
◽  
Lynn Chiu

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Biological systems may move in, feed on, socialize with, and change the world around it. How should we explain how these systems develop, act, think, and evolve? Internalists and externalists urge us to look past the entangled complexities and seek the drivers of life internally (such as genes or the brain, etc.) or externally (in the developmental, informational, social, etc. environment). Of course, everyone is an interactionist in a minimal sense, given that no system is entirely externally controlled or completely self sufficient, but sophisticated internalists and externalists think it fruitful to make intelligent bets about where to look first and how to prioritize the internal and external causes. The focus of this dissertation is externalism in evolutionary biology. Elsewhere in biology and psychology, mounting evidence that organisms maintain life activities through feedback loops with the environment have motivated theories to expand the notion of "organism" or incorporate environment as scaffolds. However, in light of all this change, the theory of natural selection has managed to stay stubbornly externalist. What I study and critique in this dissertation is the firmly held presupposition that natural selection is an environmentally driven phenomena, an assumption that drives research to almost always seek natural selection explanations of complex, plastic, and constructing systems in terms of some complex, fluctuating, challenge in the environment. It doesn't have to be. I lay down the steps that lead towards a new logic of natural selection, a form of evolution that is not necessarily driven by the environment. The first step is to figure out whether and how explanations by natural selection are externalist. Fitness, the core concept of natural selection explanations, is about how good a trait is in dealing with environmental pressures (Chapter 1). Natural selection is seen as an optimizing process that fits organisms to environment; its presence detected from correlations between organism and environment (Chapter 2). Applications of evolutionary theory outside of biology, for instance, in entrepreneurship and organization studies, export what they think are the core, defining features of natural selection, and to them, it explicitly includes an environment that is the locus of control (Chapter 3). The second step is to figure out what it takes to budge this strong externalist stance towards natural selection. Behavior, the ability of organisms to interact with their environments, is a common dividing factor in evolutionary internalist versus externalist debates. The internalist Lamarckian position postulates an "internal will" that drives organism evolution and development toward greater complexity, with the idiosyncratic use-and-disuse of the will resulting in diversity between species. The externalist Darwinian program, at its most extreme, holds that all features of the organism, including behavior, are merely passively selected for by the environment. Post-Darwin, the internalist position questions how powerful and important natural selection is for the evolution of complex traits. The anti-externalists move? To show that internal and interacting causes weaken the power of natural selection, as if natural selection explanations are always externalist. Behaviors stand at the intersection of organism and environment, and thus have been used to adjudicate internalist/externalist positions. I will thus focus on one type of behavior--niche construction: the ability of organisms to change their experienced environments--to question the staunching externalism of natural selection explanations. The last step is to move towards a different move against externalism by incorporating niche construction into natural selection, as a condition of natural selection instead of the latter's product or antagonizing force. I analyze what happens to the notion of fitness when organisms differ in fitness because of their abilities and the individual environments that are constructed, mingled, and responded to (Chapter 1). I examine theories of niche construction (Niche Construction Theory, pioneered by Kevin Laland, John Odling-Smee, and others, Dialectical Biology, by Richard Levins and Richard Lewontin, and Denis Walsh's Situated Adaptationism) to drive a distinction between niche construction as constitutive versus alternative to natural selection (Chapter 2). This last step sets the motivation and foundations for a new theory of natural selection and fitness.


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