This article argues that common intuitions regarding (a) the specialness of ‘use-novel’ data for confirmation and (b) that this specialness implies the ‘no-double-counting rule’, which says that data used in ‘constructing’ (calibrating) a model cannot also play a role in confirming the model’s predictions, are too crude. The intuitions in question are pertinent in all the sciences, but we appeal to a climate science case study to illustrate what is at stake. Our strategy is to analyse the intuitive claims in (...) light of prominent accounts of confirmation of model predictions. We show that on the Bayesian account of confirmation, and also on the standard classical hypothesis-testing account, claims (a) and (b) are not generally true; but for some select cases, it is possible to distinguish data used for calibration from use-novel data, where only the latter confirm. The more specialized classical model-selection methods, on the other hand, uphold a nuanced version of claim (a), but this comes apart from (b), which must be rejected in favour of a more refined account of the relationship between calibration and confirmation. Thus, depending on the framework of confirmation, either the scope or the simplicity of the intuitive position must be revised. 1 Introduction2 A Climate Case Study3 The Bayesian Method vis-à-vis Intuitions4 Classical Tests vis-à-vis Intuitions5 Classical Model-Selection Methods vis-à-vis Intuitions 5.1 Introducing classical model-selection methods 5.2 Two cases6 Re-examining Our Case Study7 Conclusion. (shrink)

Top scholars examine the work of Donald T. Campbell, one of the first to emphasize the social structure of science.

The concept of fitness has generated a lot of discussion in philosophy of biology. There is, however, relative agreement about the need to distinguish at least two uses of the term: ecological fitness on the one hand, and population genetics fitness on the other. The goal of this paper is to give an explication of the concept of ecological fitness by providing a reconstruction of the theory of natural selection in which this concept was framed, that is, based on the (...) way the theory was put to use in Darwin’s main texts. I will contend that this reconstruction enables us to account for the current use of the theory of natural selection. The framework presupposed in the analysis will be that of metatheoretical structuralism. This framework will provide both a better understanding of the nature of ecological fitness and a more complete reconstruction of the theory. In particular, it will provide what I think is a better way of understanding how the concept of fitness is applied through heterogeneous cases. One of the major advantages of my way of thinking about natural selection theory is that it would not have the peculiar metatheoretical status that it has in other available views. I will argue that in order to achieve these goals it is necessary to make several concepts explicit, concepts that are frequently omitted in usual reconstructions. (shrink)

This paper examines conceptual issues that arise in applications of Darwinian natural selection to cultural systems. I argue that many criticisms of cultural selectionist models have been based on an over-detailed reading of the analogy between biological and cultural units of selection. I identify five of the most powerful objections to cultural selection theory and argue that none cuts to its heart. Some objections are based on mistaken assumptions about the simplicity of the mechanisms of biological heredity. Other objections are (...) attributable, rather, to mistaken inferences from observations of biological subject matter to what is essential in natural selection. I argue that such features are idiosyncratic of biological systems, but not essential for natural selection. My arguments throughout are illustrated by examples from biological and cultural evolution, and counter-factual illustrations from the history of theoretical biology. Introduction Cultural Selection Theory First Objection: Lamarckianism Second Objection: Genotype–Phenotype Distinction Third Objection: Common Hereditary Architecture Fourth Objection: Biological Analogue for Cultural Units 6.1 Regarding strict analogues 6.2 Regarding the trait analogue 6.3 Regarding the virus analogue Fifth Objection: Environmental Interaction Conclusion CiteULike Connotea Del.icio.us What's this? (shrink)

This article argues that common intuitions regarding (a) the specialness of ‘use-novel’ data for confirmation and (b) that this specialness implies the ‘no-double-counting rule’, which says that data used in ‘constructing’ (calibrating) a model cannot also play a role in confirming the model’s predictions, are too crude. The intuitions in question are pertinent in all the sciences, but we appeal to a climate science case study to illustrate what is at stake. Our strategy is to analyse the intuitive claims in (...) light of prominent accounts of confirmation of model predictions. We show that on the Bayesian account of confirmation, and also on the standard classical hypothesis-testing account, claims (a) and (b) are not generally true; but for some select cases, it is possible to distinguish data used for calibration from use-novel data, where only the latter confirm. The more specialized classical model-selection methods, on the other hand, uphold a nuanced version of claim (a), but this comes apart from (b), which must be rejected in favour of a more refined account of the relationship between calibration and confirmation. Thus, depending on the framework of confirmation, either the scope or the simplicity of the intuitive position must be revised. (shrink)

This chapter develops the idea that the germ-soma split and the suppression of individual fitness differences within the corporate entity are not always essential steps in the evolution of corporate individuals. It illustrates some consequences for multilevel selection theory. It presents evidence that genetic heterogeneity may not always be a barrier to successful functioning as a higher-level individual. This chapter shows that levels-of-selection theorists are wrong to assume that the central problem in transitions is always that of minimizing within-group competition. (...) Evidence of intralevel conflict does not qualify as evidence against the existence of a higher level of selection. (shrink)

Observations suggesting the existence of natural antibody prior to exposure of an organism to the corresponding antigen, led to the natural selection theory of antibody formation of Jerne in 1955, and to the two signal hypothesis of Forsdyke in 1968. Aspects of these were not only first discoveries but also foundational discoveries in that they influenced contemporaries in a manner that, from our present vantage point, appears to have been constructive. Jerne’s later hypothesis (1971, European Journal of Immunology 1: 1–9), (...) that antibody-like receptors on lymphocytes were selected over evolutionary time for reactivity with the major histocompatibility complex (MHC) antigens of the species, was a first, but it was incorrect, and was foundational only to the extent that it emphasized the need to explain the Simonsen phenomenon. Although easily construed as derivative of Jerne (1971), the affinity/avidity model of Forsdyke (1975, Journal of Theoretical Biology 52: 187–198), which predicted that cell-surface components, including MHC antigens, would restrict antigen-reactivity by somatically shaping lymphocyte repertoires, was actually an extension of the two signal hypothesis. While presenting a mechanism for the positive selection of lymphocyte repertoires, and explaining the Simonsen phenomenon, the affinity/avidity model was not foundational in that it had to be independently rediscovered. For science to advance optimally we must seek to close temporal gaps so that first discoveries are also foundational. Listening to young scientists may be part of the solution. (shrink)

It has become customary in multilevel selection theory to use the same terms to denote both two explanatory goals and two explanatory means. This paper spells out some of the benefits that derive from avoiding this terminological conflation. I argue that keeping explanatory means and goals well apart allows us to see that, contrary to a popular recent idea, Price’s equation and contextual analysis—the statistical methods most extensively used for measuring the effects of certain evolutionary factors on the change in (...) the focal individual trait in multilevel selection scenarios—do not come with built-in notions of group selection and, therefore, the efficacy of these methods at analyzing various kinds of cases does not constitute a basis for deciding how group selection should best be defined. Moreover, contrary to another widely accepted idea, I argue that more than one type of group selection may serve as explanatory means when one’s goal is that of explaining the evolution of individual traits in multilevel selection scenarios and I spell out how this explanatory role should be understood. (shrink)

Interdisciplinarity is one of the features of modern science, defined as blurring the boundaries of disciplines and overcoming their limitations or excessive specialization by borrowing methods from one discipline into another, integrating different theoretical assumptions, and using the same concepts and terms. Often, theoretical knowledge of one discipline and technological advances of another are combined within an interdisciplinary science, and new branches or disciplines may also emerge. Biosemiotics, a field that arose at the crossroads of biology, semiotics, linguistics, and philosophy, (...) enables scientists to borrow theoretical assumptions from semiotics and extend them to different biological theories. The latter applies especially to extended synthesis, wherein culture is viewed as one of the factors influencing evolution. In the present research, the semiotic system of Ukrainian folk ornament is analyzed through the theory of fractals, key features of which are recursion and self-similarity. As a result, an assumption is made about the fractal structure of culture and social life on a conceptual level. What follows is a discussion of how this assumption can contribute to the multilevel selection theory, one of the foundations of extended synthesis, which employs the concept of self-similarity at all levels of the biological hierarchy. (shrink)

I clarify the difference between pluralist and monist interpretations of levels of selection disputes. Lloyd has challenged my claim that a plurality of models correctly accounts for situations such as maintenance of the sickle-cell trait, and I revisit this example to show that competing theories don’t disagree about the existence of ‘high-level’ or ‘lowlevel’ causes; rather, they parse these causes differently. Applying Woodward’s theory of causation, I analyze Sober’s distinction between ‘selection of’ versus ‘selection for’. My analysis shows that (...) this distinction separates true causes from pseudocauses, but it also reveals that the distinction is irrelevant to the levels debate; it makes no sense to say true causes are at higher levels and not lower levels. The levels debate is not about separating real causes from pseudocauses; it’s about finding useful ways to parse and disentangle causes. (shrink)

The fitness of a eukaryote hinges on the coordinated function of the products of its nuclear and mitochondrial genomes in achieving oxidative phosphorylation. I propose that sexual selection plays a key role in the maintenance of mitonuclear coadaptation across generations because it enables pre-zygotic sorting for coadapted mitonuclear genotypes. At each new generation, sexual reproduction creates new combinations of nuclear and mitochondrial genes, and the potential arises for mitonuclear incompatibilities and reduced fitness. In reviewing the literature, I hypothesize that individuals (...) engaged in mate choice select partners with correct species-typical mitochondrial and nuclear genotypes as well as individuals with highly functional cellular respiration. The implication is that mate choice for compatible nuclear and mitochondrial genes can play a significant role in generating the patterns of ornamentation and preferences observed in animals. A number of testable predictions emerge from this mitonuclear compatibility hypothesis of sexual selection. Products of mitochondrial and nuclear genes co-function to enable cellular respiration, so it is critical that compatible mitochondrial and nuclear genes be matched each generation. I propose that a core function of mate choice is selection for mitochondrial and nuclear genes that create compatible and functional combinations in offspring. (shrink)

A. W. F. Edwards is one of the most influential mathematical geneticists in the history of the discipline. One of the last students of R. A. Fisher, Edwards pioneered the statistical analysis of phylogeny in collaboration with L. L. Cavalli-Sforza, and helped establish Fisher's concept of likelihood as a standard of statistical and scientific inference. In this book, edited by philosopher of science Rasmus Grønfeldt Winther, Edwards's key papers are assembled alongside commentaries by leading scientists, discussing Edwards's influence on their (...) own research and on thinking in their field overall. In an extensive interview with Winther, Edwards offers his thoughts on his contributions, their legacy, and the context in which they emerged. This book is a resource both for anyone interested in the history and philosophy of genetics, statistics, and science, and for scientists seeking to develop new algorithmic and statistical methods for understanding the genetic relationships between and among species both extant and extinct. (shrink)

Social support networks play a key role in human livelihood security, especially in vulnerable communities. Here we explore how evolutionary ideas of kin selection and intrahousehold resource competition can explain individual variation in daily support network size and composition in a south-central Ethiopian agricultural community. We consider both domestic and agricultural help across two generations with different wealth-transfer norms that yield different contexts for sibling competition. For farmers who inherited land rights from family, firstborns were more likely to report daily (...) support from parents and to have larger nonparental kin networks. Compared with other farmers, firstborns were also more likely to reciprocate their parents’ support, and to help nonparental kin without reciprocity. For farmers who received land rights from the government, middle-born farmers reported more nonparental kin in their support networks compared with other farmers; nonreciprocal interactions were particularly common in both directions. This suggests a diversification of adult support networks to nonparental kin, possibly in response to a long-term parental investment disadvantage of being middle-born sons. In all instances, regardless of inheritance, lastborn farmers were the most disadvantaged in terms of kin support. Overall, we found that nonreciprocal interactions among farmers followed kin selection predictions. Direct reciprocity explained a substantial part of the support received from kin, suggesting the importance of the combined effects of kin selection and reciprocity for investment from kin. (shrink)

Oaksford and Chater (1994) proposed to analyse the Wason selection task as an inductive instead of a deductive task. Applying Bayesian statistics, they concluded that the cards that participants tend to select are those with the highest expected information gain. Therefore, their choices seem rational from the perspective of optimal data selection. We tested a central prediction from the theory in three experiments: card selection frequencies should be sensitive to the subjective probability of occurrence for individual cards. In Experiment 1, (...) expected frequencies of the p- and the q-card were manipulated independently by concepts referring to large vs. small sets. Although the manipulation had an effect on card selection frequencies, there was only a weak correlation between the predicted and the observed patterns. In the second experiment, relative frequencies of individual cards were manipulated more directly by explicit frequency information. In addition, participants estimated probabilities for the four logical cases and of the conditional statement itself. The experimental manipulations strongly affected the probability estimates, but were completely unrelated to card selections. This result was replicated in a third experiment. We conclude that our data provide little support for optimal data selection theory. (shrink)

In this article I summarize Friedrich Hayek’s cultural group selection theory and describe the evidence gathered by current cultural group selection theorists within the behavioral and social sciences supporting Hayek’s main assertions. I conclude with a few comments on Hayek and libertarianism.

Archer recognizes that sexual selection theory is sensitive to the effects of ecologies on sex differences, yet he does not explain the impact of such variation. For example, to what degree are there sex differences in aggression in polygynous and monogamous societies? I demonstrate how differences in mating perceptions affect the traditional dichotomy that males compete for and females choose mates.

This work takes a stand on whether Wallace should be regarded as co-author of the theory of natural selection alongside Darwin as he is usually considered on behalf of his alleged essential contribution to the conception of the theory. It does so from a perspective unexplored thus far: we will argue for Darwin’s priority based on a rational reconstruction of the theory of natural selection as it appears in the writings of both authors. We show that the theory does not (...) appear in exactly the same manner in the writings of each of its alleged co-discoverers: tough we find the same fundamental elements in both works, even in Darwin’s early texts, we discern a more complex unifying and ramified structure than the one we find in Wallace’s Ternate manuscript. Even when we think the badge of the “Darwin–Wallace” theory is well deserved, the unifying force of Darwin’s version has proved to be one of the keys for the ulterior success of the so-called Darwinian revolution in Biology. (shrink)

Selection type theories solve adaptation problems. Natural selection, clonal selection for antibody production, and selective theories of higher brain function are examples. An abstract characterization of typical selection processes is generated by analyzing and extending previous work on the nature of natural selection. Once constructed, this abstraction provides a useful tool for analyzing the nature of other selection theories and may be of use in new instances of theory construction. This suggests the potential fruitfulness of research (...) to find other theory types and construct their abstractions. (shrink)

This book puts multilevel selection theory into a much needed historical perspective. This is achieved by discussing multilevel selection in the first half of the twentieth century, the reasons for the energetic rejection of Wynne-Edwards’ group selectionist stance in the 1960s, Elisabeth Lloyd’s contribution to the units of selection debate, Price’s hierarchical equation and its possible interpretations and, finally, species selection in macroevolutionary contexts. Another idea also seems to emerge from these studies; namely, that perhaps a more sure-footed position for (...) multilevel selection theory would be acquired if we were to show a renewed interest in 'old group selection', i.e. in scenarios in which the differential reproduction of the groups themselves affects the frequencies of either individual-level or group-level traits. This book will be of interest to philosophers and historians of biology, as well as to theoretically inclined biologists who have an interest in multilevel selection theory. (shrink)

Contemporary empiricism has attempted to ground its analysis of science in a falsificationism based in selection theory. This paper links these evolutionary epistemologies with commitments to certain epistemological and ontological assumptions found in the later work of K. Popper, D. Campbell, and D. Hull, I argue that their assumptions about the character of contemporary empiricism are part of a shared paradigm of epistemological explanation which results in unresolved tensions within their own projects. I argue further that their claim to be (...) doing a science of science is not defensible. Hull's selectionism is analyzed to show how this epistemological agenda has played itself out in late empiricism. I suggest some directions that Hull might take toward an historical epistemology. (shrink)

Two controversies exist regarding the appropriate characterization of hierarchical and adaptive evolution in natural populations. In biology, there is the Wright-Fisher controversy over the relative roles of random genetic drift, natural selection, population structure, and interdemic selection in adaptive evolution begun by Sewall Wright and Ronald Aylmer Fisher. There is also the Units of Selection debate, spanning both the biological and the philosophical literature and including the impassioned group-selection debate. Why do these two discourses exist separately, and interact relatively little? (...) We postulate that the reason for this schism can be found in the differing focus of each controversy, a deep difference itself determined by distinct general styles of scientific research guiding each discourse. That is, the Wright-Fisher debate focuses on adaptive process, and tends to be instructed by the mathematical modeling style, while the focus of the Units of Selection controversy is adaptive product, and is typically guided by the function style. The differences between the two discourses can be usefully tracked by examining their interpretations of two contested strategies for theorizing hierarchical selection: horizontal and vertical averaging. (shrink)

The greatest challenge for Cultural Selection Theory lies is the paucity of evidence for structural mechanisms in cultural systems that are sufficient for adaptation by natural selection. In part, clarification is required with respect to the interaction between cultural systems and their purported selective environments. Edmonds et al. have argued that Cultural Selection Theory requires simple, conclusive, unambiguous case studies in order to meet this challenge. To that end, this paper examines the songs of the Rufous-collared Sparrow, which seem (...) to exhibit cultural adaptations minimizing signal degradation relative to local environments. Specifically, the more forested the habitat, the more the tail end of the song resembles a whistle rather than a trill; yet, variation in song is uncorrelated with genetic variation. This paper explores the mechanisms responsible for these putative acoustic adaptations through a series of computer simulations. The main point of this research is not to test this model, but to demonstrate that models of this type have the resources to meet the in-principle objections that have been raised against Cultural Selection Theory. This research lends much-needed empirical support to Cultural Selection Theory by clarifying the nature of the interaction between culture and environment. It also contributes to evolutionary theory by clarifying the scope and limits of adaptation by natural selection. (shrink)

In this paper we argue that sensory exploitation, a model from sexual selection theory, deserves more attention in evolutionary thinking about art than it has up until now. We base our argument on the observation that in the past sensory exploitation may have been underestimated in sexual selection theory but that it is now winning field. Likewise, we expect sensory exploitation can play a more substantial role in modeling the evolution of art behavior. Darwin's theory of sexual selection provides a (...) mechanistic basis to explain the evolution of male display traits. This mechanistic approach has proven useful to developing hypotheses about the evolution of human art. Both Boyd and Richerson (1985) and Miller (1998, 1999, 2000, 2001) have applied an indirect-benefit model from sexual selection to the evolution of art behavior. We argue that the mechanistic possibilities sensory exploitation has to offer as a model have remained underexplored so far, so we propose a concept based upon it. From the sensory exploitation perspective it follows that exaptive exploitation of psychosensory biases is a primary force in the evolution of art production (notice that the use of a model from sexual selection does not imply art evolved as a sexual display - we only use it for its mechanism) and that the indirect-benefit model only provides secondary forces. Thus, sensory exploitation may operate alone under some conditions but usually secondary processes as a result of indirect benefits are expected to kick in. The concept of sensory exploitation will need to play a central role in articulating all of the existing hypotheses about art. (shrink)

In a recent issue of this journal, Vandermassen suggested that feminists should include sexual selection theory and evolutionary psychology in a unifying theory of human nature. In response, this article aims to offer some insight into the development of sexual selection theory, to caution against Vandermassen's unreserved assimilation and to promote the opposite ongoing integration — an inclusion of gender perspectives into evolutionary biology. In society today, opinions about maintaining traditional sex roles are often put forward on the basis of (...) what is natural and how animals behave. However, the natural sciences have proved to be pervaded by gendered values and interests; Darwin's theory of sexual selection has been criticized for being male biased, and partly due to the unwillingness of Darwin's scientific contemporaries to accept female choice, research has been overwhelmingly focused on males. More recently, theory has become less gender biased and research has come to include a large variety of issues not present in the first version of the theory. However, there is a need to increase the awareness of gender bias in order to develop a gender-neutral evolutionary biology. (shrink)

Williams and J. Fraser have recently argued that effective field theory methods enable scientific realists to make more reliable ontological commitments in quantum field theory than those commonly made. In this paper, I show that the interpretative relevance of these methods extends beyond the specific context of QFT by identifying common structural features shared by effective theories across physics. In particular, I argue that effective theories are best characterized by the fact that they contain intrinsic empirical limitations, and (...) I extract from their structure one central interpretative constraint for making more reliable ontological commitments in different subfields of physics. While this is in principle good news, this constraint still raises a challenge for scientific realists in some contexts, and I bring the point home by focusing on Williams’s and J. Fraser’s defense of selective realism in QFT. (shrink)

Our social role/biosocial theory provides a more adequate account of aggression sex differences than does Archer's sexual selection theory. In our theory, these sex differences arise flexibly from sociocultural and ecological forces in interaction with humans' biology, as defined by female and male physical attributes and reproductive activities. Our comments elaborate our theory's explanations for the varied phenomena that Archer presents.

In this short paper, I argue against what I call the “belonging to” interpretation of group selection in scenarios in which a group’s fitness is defined as the per capita reproductive output of the individuals of the group. According to this interpretation, group selection acts on “belonging to” properties of individuals, i.e. on relational or contextual properties that all the individuals of a group share simply by belonging to that group; thus, if differences in the individuals’ “belonging to” properties cause (...) differences in their fitness, group selection sensu the “belonging to” interpretation is said to be at work. I argue that the main problem with the “belonging to” interpretation is that it confuses evolutionary changes due to differences in environmental quality with evolutionary changes due to selection. In other words, I argue that, in the majority of cases, this interpretation actually takes the “selection” out of the “group selection” notion it aims to interpret: by adopting this perspective, one implicitly commits to explaining the evolutionary change under consideration not by a kind of selection, but by differences in the environmental quality experienced by individual types. (shrink)

This article considers the application of sexual selection theory to the study of religion by discussing the basic concepts and theories in sexual selection and then outlines possibilities of its application to the study of the evolution of religion. The first section outlines basic principles in the sexual selection account, including the evolution of human mating strategies based on dimorphism, gender differences in human mating strategies, and the role of different cultural activities in mating dynamics. Such an overview may (...) be useful for the readers who are less familiar with the basic assumptions of the sexual selection theory. The remaining sections demonstrate how religion may function as a signal for mating qualities associated with a long-term mating strategy and how different facets of religiosity may help to support long-term mating strategies. The key idea of the article is that there are good reasons to try to explain the evolution of at least some of the components of religion in terms of sexual selection. (shrink)

A monadic formula Ψ (Y) is a selector for a formula φ (Y) in a structure M if there exists a unique subset P of μ which satisfies Ψ and this P also satisfies φ. We show that for every ordinal α ≥ ωω there are formulas having no selector in the structure (α, <). For α ≤ ω₁, we decide which formulas have a selector in (α, <), and construct selectors for them. We deduce the impossibility of a full (...) generalization of the Büchi-Landweber solvability theorem from (ω, <) to (ωw, <). We state a partial extension of that theorem to all countable ordinals. To each formula we assign a selection degree which measures "how difficult it is to select". We show that in a countable ordinal all non-selectable formulas share the same degree. (shrink)

This work is derived from the SERC "Logic for IT" Summer School Conference on Proof Theory held at Leeds University. The contributions come from acknowledged experts and comprise expository and research articles which form an invaluable introduction to proof theory aimed at both mathematicians and computer scientists.

According to scientific realists, the predictive success of mature theories provides a strong epistemic basis for thinking that such theories are approximately true. However, we know that many theories once regarded as well-confirmed and predictively successful were eventually replaced with successor theories, and some claim this undermines the epistemic confidence we should have in the approximate truth of current science. Selective scientific realists in turn argue that if one can show that the predictive success of (...) some rejected theory T is a function of theoretical claims consistent with current science, then T’s failure doesn’t undermine the claim that current successful theories are approximately true. As such, Selective Scientific Realism (SSR) can be tested through historical examples. Showing that the predictive success of a failed theory is the result of theoretical features later rejected provides a counterexample to SSR. Conversely, SSR is supported if its explanation of the predictive success of failed theories--namely, that the factors which lead to predictive success in the failed theory survive in the successor theory--is able to handle a wide array of historical cases. (shrink)

In both biology and the human sciences, social groups are sometimes treated as adaptive units whose organization cannot be reduced to individual interactions. This group-level view is opposed by a more individualistic one that treats social organization as a byproduct of self-interest. According to biologists, group-level adaptations can evolve only by a process of natural selection at the group level. Most biologists rejected group selection as an important evolutionary force during the 1960s and 1970s but a positive literature began to (...) grow during the 1970s and is rapidly expanding today. We review this recent literature and its implications for human evolutionary biology. We show that the rejection of group selection was based on a misplaced emphasis on genes as "replicators" which is in fact irrelevant to the question of whether groups can be like individuals in their functional organization. The fundamental question is whether social groups and other higher-level entities can be "vehicles" of selection. When this elementary fact is recognized, group selection emerges as an important force in nature and what seem to be competing theories, such as kin selection and reciprocity, reappear as special cases of group selection. The result is a unified theory of natural selection that operates on a nested hierarchy of units. The vehicle-based theory makes it clear that group selection is an important force to consider in human evolution. Humans can facultatively span the full range from self-interested individuals to "organs" of group-level "organisms." Human behavior not only reflects the balance between levels of selection but it can also alter the balance through the construction of social structures that have the effect of reducing fitness differences within groups, concentrating natural selection (and functional organization) at the group level. These social structures and the cognitive abilities that produce them allow group selection to be important even among large groups of unrelated individuals. (shrink)