Levels and Units of Selection

Human knowledge is a phenomenon whose roots extend from the cultural, through the neural and the biological and finally all the way down into the Precambrian “primordial soup.” The present paper reports an attempt at understanding this Greater System of Knowledge (GSK) as a hierarchical nested set of selection processes acting concurrently on several different scales of time and space. To this end, a general selection theory extending mainly from the work of Hull and Campbell is introduced. The perhaps most (...) drastic change from previous similar theories is that replication is revealed as a composite function consisting of what is referred to as memory and synthesis. This move is argued to drastically improve the fit between theory and human-related knowledge systems. The introduced theory is then used to interpret the subsystems of the GSK and their interrelations. This is done to the end of demonstrating some of the new perspectives offered by this view. (shrink)

Mesoudi et al. argue that the current inability to identify the means by which cultural traits are acquired does not debilitate their project to draw clear parallels between cultural and biological evolution. However, I suggest that cultural phenomena may be accounted for by biological processes, unless we can identify a cultural “genotype” that carries information from person to person independently of genes. (Published Online November 9 2006).

If temperature does not vary from one generation from to the next but its value is crucial for the development of particular phenotypic characteristics, a long-term change in its value may trigger major evolutionary changes of the organism. If a bird's nest maintains the critical temperature, then a statement that the bird is the nest's way of making another nest is as helpful as accounts couched in terms of genes' intentions. However, the language of intentions rests on different evidence and (...) assumptions from causal language and the languages are not interchangeable. Understanding ontogeny in causal terms requires explanations that are made as simple as possible but not so simple that they become completely unrealistic. (shrink)

When one takes the evolution of operant behavior as prototype, one sees that the term replication is too tied to the peculiarities of genetic evolution. A more general term is recurrence. The important problem raised by recurrence is not “information” but relationship: deciding when two occurrences belong to the same lineage. That is solved by looking at common environmental effects.

Ernst Mayr''s distinction between ultimate and proximate causes is justly considered a major contribution to philosophy of biology. But how did Mayr come to this philosophical distinction, and what role did it play in his earlier scientific work? I address these issues by dividing Mayr''s work into three careers or phases: 1) Mayr the naturalist/researcher, 2) Mayr the representative of and spokesman for evolutionary biology and systematics, and more recently 3) Mayr the historian and philosopher of biology. If we want (...) to understand the role of the proximate/ultimate distinction in Mayr''s more recent career as a philosopher and historian, then it helps to consider hisearlier use of the distinction, in the course of his research, and in his promotion of the professions of evolutionary biology and systematics. I believe that this approach would also shed light on some other important philosophical positions that Mayr has defended, including the distinction between essentialism: and population thinking. (shrink)

Various results show the ‘formal equivalence’ of kin and group selectionist methodologies, but this does not preclude there being a real and useful distinction between kin and group selection processes. I distinguish individual and population-centred approaches to drawing such a distinction, and I proceed to develop the latter. On the account I advance, the differences between kin and group selection are differences of degree in the structural properties of populations. A spatial metaphor provides a useful framework for thinking about these (...) differences: kin and group selection may be conceptualized as large, overlapping regions of K-G space. I then consider some implications of the account, defend it from possible objections, and further argue that the structural features characteristic of both kin and group selection may recur at multiple levels of biological organization. (shrink)

In a recent paper, Potochnik (Biol Philos 24(2):183–197, 2009) analyses some uses of optimality modelling in light of the anti-adaptationism criticism. She distinguishes two broad classes of such uses (weak and strong) on the basis of assumptions held by biologists about the role and the importance of natural selection. This is an interesting proposal that could help in the epistemological characterisation of some biological practices. However, Potochnik’s distinction also rests on the assumption that all optimality modelling represent the selection dynamic (...) involved in the system of phenomena being considered. Since this assumption does not hold for models belonging to optimal foraging theory (OFT)—one of behavioural ecology’s important modelling traditions—Potochnik’s proposal has to be critically reappraised. In this paper, we briefly discuss what is optimality modelling and what it means for a model to represent a dynamic of selection or of evolution. Then, we demonstrate that OFT modelling is unable to represent either past or contemporary selection dynamics. In order to make this point, we carefully delineate the theory’s rationale. This allows us to identify and analyse the assumptions on which the theory is built, and to circumscribe precisely the role that natural selection plays in it. Next, we show that the distinction of weak and strong uses of optimality modelling is seriously weakened when OFT modelling is taken into account. More precisely, the distinction is either irrelevant (if the assumption that selection dynamics are represented in all optimality modelling is held) or of a modest utility (if the assumption is dropped). However, we suggest that Potochnik’s original proposal could be saved, and that it even constitutes a tool to appraise the marks left in the literature by the evolution of optimality modelling practices in the last four decades, provided that it is made into a tripartite distinction. (shrink)

A recent development in biology has been the growing acceptance that holobionts, entities comprised of symbiotic microbes and their host organisms, are widespread in nature. There is agreement that holobionts are evolved outcomes, but disagreement on how to characterize the operation of natural selection on them. The aim of this paper is to articulate the contours of the disagreement. I explain how two distinct foundational accounts of the process of natural selection give rise to competing views about evolutionary individuality.

Following Wallace’s suggestion, Darwin framed his theory using Spencer’s expression “survival of the fittest”. Since then, fitness occupies a significant place in the conventional understanding of Darwinism, even though the explicit meaning of the term ‘fitness’ is rarely stated. In this paper I examine some of the different roles that fitness has played in the development of the theory. Whereas the meaning of fitness was originally understood in ecological terms, it took a statistical turn in terms of reproductive success throughout (...) the 20th Century. This has lead to the ever-increasing importance of sexually reproducing organisms and the populations they compose in evolutionary explanations. I will argue that, moving forward, evolutionary theory should look back at its ecological roots in order to be more inclusive in the type of systems it examines. Many biological systems can only be satisfactorily accounted for by offering a non-reproductive account of fitness. This argument will be made by examining biological systems with very small or transient population structures. I argue this has significant consequences for how we define Darwinism, increasing the significance of survival over that of reproduction. (shrink)

Richard Lewontin's (1970) early work on the units of selection initiated the conceptual and theoretical investigations that have led to the hierarchical perspective on selection that has reached near consensus status today. This paper explores other aspects of his work, work on what he termed continuity and quasi-independence, that connect to contemporary explorations of modularity in development and evolution. I characterize such modules and argue that they are the true units of selection in that they are what evolution by natural (...) selection individuates, selects among, and transforms. (shrink)

Sober (1992) has recently evaluated Brandon's (1982, 1990; see also 1985, 1988) use of Salmon's (1971) concept of screening-off in the philosophy of biology. He critiques three particular issues, each of which will be considered in this discussion.

This anthology collects some of the most important papers on what is believed to be the major force in evolution, natural selection. An issue of great consequence in the philosophy of biology concerns the levels at which, and the units upon which selection acts. In recent years, biologists and philosophers have published a large number of papers bearing on this subject. The papers selected for inclusion in this book are divided into three main sections covering the history of the subject, (...) explaining its conceptual foundations, and focusing on kin and group selection and higher levels of selection.One of the book's interesting features is that it draws together material from the biological and philosophical literatures. The philosophical literature, having thoroughly absorbed the biological material, now offers conceptual tools suitable for the reworking of the biological arguments. Although a full symbiosis has yet to develop, this anthology offers a unique resource for students in both biology and philosophy.Robert N. Brandon is Professor in the Philosophy Department, Duke University. Richard M. Burian is Professor of Philosophy and Department Chairman, Virginia Polytechnic Institute and State University.A Bradford Book. (shrink)

The question "what is (are) the unit(s) of selection" can be interpreted in three different ways. These interpretations are discussed and it is shown that they prompt different answers; such units are shown to be individuals in the context of the given interpretation. One of these interpretations is argued, by examples, not always to have an unambiguously correct answer. An alternative approach to this question is sketched.

Hull et al. rightly point out the special character of selection as a causal mode, but ironically they seem to force selection back into traditional causal modes by decomposing it into replication, variation, and environmental interaction. Many processes are selective, and a taxonomy of a broad range of kinds of selection may be preferable to narrowing the applicability of the term.

I argue for the usefulness of the evolutionary kind of biological individual.

What changes when an evolutionary transition in individuality takes place? Many different answers have been given, in respect of different cases of actual transition, but some have suggested a general answer: that a major transition is a change in the extent to which selection acts at one hierarchical level rather than another. The current paper evaluates some different ways to develop this general answer as a way to characterise the property ‘evolutionary individuality’; and offers a justification of the option taken (...) in Clarke :413–435, 2013)—to define evolutionary individuality in terms of an object’s capacity to undergo selection at its own level. In addition, I suggest a method by which the property can be measured and argue that a problem which is often considered to be fatal to that method—the problem of ‘cross-level by-products’—can be avoided. (shrink)

Hull et al. see responses and properties of responses as units of selection in behavioral change. However, this perspective cannot account for goal-directed behavior in which organisms employ variable means to reliably attain intended consequences. An alternative perspective is offered in which the intended consequences (goals) of behavior serve as the units of selection in behavior change.

Communication and recognition are essential for social life. Social insects are good model systems to study social behavior and complexity because their societies are evolutionarily stable and ecologically successful. Ants, in particular, show a large variety of adaptations and are extremely diverse. In ants, social interactions are regulated by at least three levels of recognition. Nestmate recognition occurs between colonies, is very effective, and involves fast processing. Within a colony, division of labor is enhanced by recognition of different classes of (...) individuals. Ultimately, in particular circumstances, such as cooperative colony founding with stable dominance hierarchies, ants are capable of individual recognition. The underlying recognition cues and mechanisms appear to be specific to each recognition level, and their integrated understanding could contribute to the identification of the minimum requirements for the emergence of sociality. (shrink)

The group selection controversy largely focuses on altruism (e.g., Wilson 1983; Lloyd 2001; Shavit 2004; Okasha 2006, 173ff; Borrello 2010; Leigh 2010; Rosas 2010; Hamilton and Dimond in press). Multilevel selection theory is a resolution of this controversy. Whereas kin selection partitions inclusive fitness into direct and indirect components (via influencing the replication of copies of genes in other individuals), multilevel selection considers within-group and between-group components of fitness (Gardner et al. 2011; Lion et al. 2011). Two scenarios of multilevel (...) selection are often distinguished (Damuth and Heisler 1988; Okasha 2006; Pigliucci 2010): (1) group structure only divides individual fitnesses into within- and between-group components (MLS1); and, (2) groups get their own component of fitness and also, in most definitions, a group-level adaptation (MLS2). (shrink)

Hierarchical expansions of the theory of natural selection exist in two distinct bodies of thought in evolutionary biology, the group selection and the species selection traditions. Both traditions share the point of view that the principles of natural selection apply at levels of biological organization above the level of the individual organism. This leads them both to considermultilevel selection situations, where selection is occurring simultaneously at more than one level. Impeding unification of the theoretical approaches of the multilevel selection traditions (...) are the different goals of investigators in the different subdisciplines and the different types of data potentially available for analysis. We identify two alternative approaches to multilevel situations, which we termmultilevel selection [1] andmultilevel selection [2]. Of interest in the former case are the effects of group membership onindividual fitnesses, and in the latter the tendencies for the groups themselves to go extinct or to found new groups (i.e., group fitnesses). We argue that: neither represents the entire multilevel selection process; both are aspects of any multilevel selection situation; and both are legitimate approaches, suitable for answering different questions. Using this formalism, we show that: multilevel selection [2] does not require emergent group properties in order to provide an explanatory mechanism of evolutionary change; multilevel selection [1] is usually more appropriate for neontological group selection studies; and species selection is most fruitfully considered from the point of view of multilevel selection [2]. Finally we argue that the effect hypothesis of macroevolution, requiring, in selection among species, both the absence of group effects on organismic fitness (multilevel selection [1]), and the direct determination of species fitnesses by those of organisms, is untestable with paleontological data. Furthermore, the conditions for the effect hypothesis to hold are extremely restrictive and unlikely to apply to the vast majority of situations encountered in nature. (shrink)

Although "intrasexual selection" has been accepted as the mechanism by which males evolve elaborate secondary sexual traits which are used in aggressive contests, the importance of "intersexual selection" as a mechanism by which males have acquired exaggerated traits to display to females during courtship was less readily accepted. In spite of this scepticism, several genetic models have supported the latter idea, and many empirical studies showed that females were generally more discriminating in mate choice than males, because of differences in (...) relative investment between sexes. Nowadays, this idea is reinforced by various concepts (parental investment, potential reproductive rate, environmental potential for polygamy...) which stress that the strength of sexual selection is related to many interdependent factors, such as mating systems, resource distribution (food, habitat, mate), life history and other ecological characteristics. The case of Salmonids is presented here to show how novel information on sexual selection has contributed to the understanding of the plasticity of breeding patterns in the context of evolutionary biology. (shrink)

The question asked in this article is: what is a parasite?. Defining a parasite requires defining its host at the same time. A difficult question therefore arises about host-parasite relationships. The object of general parasitology is in fact to study the relationship between a host and its parasite. The initial question what is a parasite? has to be reformulated within a conceptual framework, that of relationship. This article is an attempt to transpose into parasitology some concepts which have been profitable (...) in the fields of physics and chemistry. The studies of R. Thom about the individual are also used. Concepts like that of field and principles like that of minimization are probably operational on a high level of organization. The description of host-parasite relationships could benefit from these concepts. (shrink)

It has increasingly been recognised that units of biological classification cannot be identified with the units of evolution. After briefly defending the necessity of this distinction I argue, contrary to the prevailing orthodoxy, that species should be treated as the fundamental units of classification and not, therefore, as units of evolution. This perspective fits well with the increasing tendency to reject the search for a monistic basis of classification and embrace a pluralistic and pragmatic account of the species category. It (...) also provides a diagnosis of the paradoxical but popular idea that species are individuals: Species are not individuals, but the units of evolution are. (shrink)

Selection in behavior analysis fits the criteria of replication, variation and interaction proposed by the authors except for information under replication. If information requires physical structure, behavior analysis does not fit that model because functional analysis may provide parallels between behavior, neurology, and biochemistry but not sequencing. The three sciences are not unified by the model but another is available.

Multi-level selection can be understood via the Price equation or contextual analysis, which offer incompatible statistical decompositions of evolutionary change into components of group and individual selection. Okasha argued that each approach suffers from problem cases. I introduce further problem cases for the Price approach, arguing that it is appropriate for MLS 2 group selection but not MLS 1. I also show that the problem cases Okasha raises for contextual analysis can be resolved. For some such cases, however, it emerges (...) that there is no determinate answer to the question of how much of the total selective effect was due to group selection compared to individual selection. This suggests that when there is interaction between the effect of group character and individual character, one cannot separate selection into distinct ‘levels’ at all. (shrink)

A profound problem in viewing operant learning as selection appears to be the identification of replicators. Given the lack of consensus on what constitutes the appropriate unit of analysis for behavior, there may be multiple levels at which the metaphor of selection may be usefully applied. A final difficulty: The elements of selection in the evolution of species are objects. In behavior, they are events.

Sightings of the revolutionary comet that appeared in the skies of evolutionary biology in 1976—the selfish gene—date back to the 19th and early 20th centuries. It became generally recognized that genes were located on chromosomes and compete with each other in a manner consistent with the later appellation “selfish.” Chromosomes were seen as disruptable by the apparently random “cut and paste” process known as recombination. However, each gene was only a small part of its chromosome. On a statistical basis a (...) gene should escape disruption for many generations. This led George Williams and Richard Dawkins to a new definition of the gene, differing from conventional biochemical definitions in that there were no consistent genic boundaries. There had been no previous sightings of another revolutionary, albeit less verbally spectacular, comet that appeared in 1975—the homostability principle of Akiyoshi Wada. Each gene has a base composition “accent” that distinguishes it from its neighbors. We now see that recombination can be triggered by the shift in base composition at genic boundaries. Hence, the Williams-Dawkins definition approaches the conventional definitions. (shrink)

An idea is not a replicator because it does not consist of coded self-assembly instructions. It may retain structure as it passes from one individual to another, but does not replicate it. The cultural replicator is not an idea but an associatively-structured network of them that together form an internal model of the world, or worldview. A worldview is a primitive, uncoded replicator, like the autocatalytic sets of polymers widely believed to be the earliest form of life. Primitive replicators generate (...) self-similar structure, but because the process happens in a piecemeal manner, through bottom-up interactions rather than a top-down code, they replicate with low fidelity, and acquired characteristics are inherited. Just as polymers catalyze reactions that generate other polymers, the retrieval of an item from memory can in turn trigger other items, thus cross-linking memories, ideas, and concepts into an integrated conceptual structure. Worldviews evolve idea by idea, largely through social exchange. An idea participates in the evolution of culture by revealing certain aspects of the worldview that generated it, thereby affecting the worldviews of those exposed to it. If an idea influences seemingly unrelated fields this does not mean that separate cultural lineages are contaminating one another, because it is worldviews, not ideas, that are the basic unit of cultural evolution. (shrink)

The paper argues for a pragmatic account of genetic explanation. This is to say that when a disease or other trait is termed genetic, the reasons for singling out genes as causes over other, also necessary, genetic and nongenetic conditions are not wholly theoretical but include pragmatic dimensions. Whether the explanation is the presence of a trait in an individual or differences in a trait among individuals, genetic explanations are context-dependent in three ways: they are relative to a causal background (...) of genetic and nongenetic factors; they are relative to a population; and they are relative to the present state of knowledge. Criteria like causal priority, nonstandardness, and causal efficacy that purport to distinguish objectively between genetic causes and nongenetic conditions either incorporate pragmatic elements or fail for other reasons. When the pragmatic dimensions of genetic explanations are recognized, we come to understand the current phenomenon of geneticization to be a reflection of increased technological capacities to manipulate genes in the laboratory, and potentially the clinic, rather than theoretical progress in understanding how diseases and other traits arise. This calls into question the value of the search for theoretical definitions of designations like genetic disease or genetic susceptibility as directives for action. (shrink)

Edward O. Wilson’s recent decision to abandon kin selection theory has sent shockwaves throughout the biological sciences. Over the past two years, more than a hundred biologists have signed letters protesting his reversal. Making sense of Wilson’s decision and the controversy it has spawned requires familiarity with the historical record. This entails not only examining the conditions under which kin selection theory first emerged, but also the organicist tradition against which it rebelled. In similar fashion, one must not only examine (...) Wilson’s long career, but also those thinkers who influenced him most, especially his intellectual grandfather, William Morton Wheeler (1865–1937). Wilson belongs to a long line of organicists, biologists whose research highlighted integration and coordination, many of whom struggled over the exact same biological riddles that have long defined Wilson’s career. Drawing inspiration (and sometimes ideas) from these intellectual forebears, Wilson is confident that he has finally identified the origin of the social impulse. (shrink)