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This chapter looks at the ‘major evolutionary transitions’, in particular the idea that multi-level selection theory is crucial for understanding them. These transitions occur when a number of free-living biological individuals, originally capable of surviving and reproducing alone, become integrated into a co-operative whole. The literature on evolutionary transitions is concerned with the origins of hierarchical organization rather than selection and adaptation at pre-existing hierarchical levels. This calls for a ‘diachronic’ rather than a ‘synchronic’ formulation of the levels of selection question. The implications of this change in perspective are examined. The distinction between MLS1 and MLS2 is examined in relation to the major evolutionary transitions.

The complexity of the living world can be described as a series of evolutionary transitions. A subset of these are the ETIs (evolutionary transitions in individuality), the theory of which explains how individuals of one kind go through cycles of conflict, conflict mediation and cooperation to eventually become individuals of another kind. The theory of ETIs and multilevel selection can be applied to the origin of life. The interpretive view expanded on in this chapter, is not only of epistemic value but it is helpful to explain the increase in genetic information that was essential for more complex life to evolve. At the origin of life, lower-level replicating units (LRUs) cooperated to form higher-level replicating units (HRUs) from which the simplest proto-cells emerged. Trade-offs in reproduction and viability and task allocation between individuals at the lower level facilitated the transfer of fitness to higher level individuals. Where possible, exemplars of LRUs (like mobile genetic elements) and HRUs (primitive, but functionally integrated groups of ribozymes and/or genes) are used for explanatory purposes.

This chapter presents a displacement of the organism as a privileged level of analysis in evolutionary biology. It is concerned with the ontology of biology systems, with particular reference to hierarchical organization. It argues that the concept of a rank-free hierarchy can be transposed to the major transitions hierarchy, with interesting consequences. This chapter shows that the idea of rank freedom makes good sense of a number of facets of the recent discussion of evolutionary transitions and multilevel selection. It suggests that the idea of rank freedom is already at work, implicitly, in much theorizing about evolutionary transitions and/or multilevel selection.

The hierarchy theory at its onset was primarily committed to vindicate the distinctness of macro-evolutionary phenomena from micro-evolutionary processes, minimizing the explanatory relevance of levels and entities below the organism and above the gene. The current focus on phenotypic evolution, however, suggests a refinement and revision of the role of the so-called “somatic” or “phenotypic hierarchy”, and the evolutionary bearing of its structured variability at different levels. The paper reviews some theoretical reasons and implications of such reassessment.

This chapter reviews the debate on group selection, a concept that has experienced vertiginous ups and downs since the 1960s, and brings it up to modern standards within the broader context of multilevel selection (MLS) theory. It specifically offers a brief overview of MLS theory, major evolutionary transitions, and human evolution as a major transition, so that these subjects can become part of an extended evolutionary synthesis. The chapter also describes how MLS theory relates to the Modern Synthesis. A comment on all aspects of human behavior and culture from an evolutionary perspective is then presented.

This chapter describes the evolutionary transition from single cells to multicellular individuals. It shows that in multicellular organisms, individuality is ultimately a property of individual cells that give rise to a multicellular organism in each generation. It then investigates the breakdown of cooperation, in the course of developing a heterodox idea on the origins of the germ-soma distinction. It examines the evolution of multicellular development in the Pseudomonas system by introducing a discrete-time theoretical model. The described unconventional life cycles that span the multilevel selection (MLS)-1 to MLS-2 juncture are founded in experimental reality.

Although life history trade-offs are recognized as central to life history evolution, the mechanisms underlying trade-offs are not well understood. Life history trade-offs gain unique significance during evolutionary transitions in individuality (such as the transitions from unicellular to multicellular individuals and solitary individuals to eusocial societies). This chapter develops further this proposal using the volvocalean green algal group as a model system. First, it introduces the volvocalean algae and discusses the aspects of their life history that are relevant to the evolution of multicellularity in this lineage. Then, it briefly reviews what is known about the mechanistic basis of acclimation – a specific adaptive response to environmental changes that magnifies the survival–reproduction trade-off in these algae. Last, the chapter considers the genetic basis for the differentiation of germ and somatic cells in the most complex member of this lineage, Volvox carteri. It proposes a hypothesis for the evolution of somatic cells in which, by simulating the general acclimation signal (i.e., a change in the redox status of the cell) in a spatial rather than temporal context, a life history trade-off gene associated with ensuring long-term survival at a cost to immediate reproduction can be co-opted into a ‘specialization’ gene – that is, a gene whose differential expression between cells gives rise to specialized cell types. In this way, individual cells in a group are released from the survival–reproduction trade-off that constrains their unicellular relatives, and the two fitness components can be maximized independently and simultaneously.

There exist many definitions of human joint action. However, they do not agree and are not directly reducible to each other. This multiplicity is due to a lack of constraints on them. This chapter argues that they should at least meet an efficiency constraint: any account of joint action has to justify how it reliably leads agents to cooperation. One avenue consists in exploring the analogy between definitions of joint action and of biological individuality. The main components for biological individuality have been identified and their relations are much better understood than those between the components of human joint action. The chapter shows that there are surprisingly strong analogies between the criteria and mechanisms for joint action and for biological individuality. As a result, we can import some insights of the biological literature to define what a joint action is, and when a group can and should be considered as an individual.

Part II is about origins: how do new traits arise from old phenotypes? People of all ages are fascinated by the question of origins. Origins are the common concern of evolutionists and creationists, of ethnic historians, of Mormon geneologists and the Daughters of the American Revolution, of adopted children searching for their biological parents— indeed, of all who have wondered where Johnny got his patience, his sense of humor, or his big nose. Darwin was a clever publicist when he titled his most famous book The Origin of Species. He touched deep human chords by discussing not only the origin of species but the origin of marvellously complex morphological and psychological traits—specialized limbs, sexual behavior, intelligence, heroism, and the vertebrate eye, to mention just a few. Research on selection and adaptation may tell us why a trait persisted and spread, but it will not tell us where a trait came from. This is why evolutionary biology inevitably intersects with developmental biology, and why satisfactory explanations of ultimate (evolutionary) causation must always include both proximate causes and the study of selection. Novel traits originate via the transformation of ancestral phenotypes during development. This transformational aspect of evolutionary change has been oddly neglected in modern evolutionary biology, even though it is an integral part of human curiosity about origins in other fields. From classical mythology to modern-day childrens’ books, origins are explained in terms of transformations of the phenotype, alongside attention to developmental mechanisms and adaptive functions. Consider this excerpt from The Apeman’s Secret (Dixon, 1980), a Hardy Boys adventure book: . . . [T]he Apeman hated cruelty of any kind. Whenever he saw crooks or villians do something nasty to a helpless victim, he would fly into a rage. This would change his body chemistry and cause him to revert to the savage state. . . .

This chapter develops a subtle model that integrates environmental and internal factors. It describes the phylogenetic distribution of multicellular organisms in general and complex multicellular life in particular, clarifying the important distinction between the two. This chapter shows that the long apparent lag between the appearance of simple multicellularity in eukaryotes and the radiation of groups with complex multicellular organization has an environmental component that can be associated back to the consequences of life with interior and exterior cells. It suggests that the evolutionary transition from unicells to complex multicellular organisms has several steps.

Parental care is any parental trait that enhances the fitness of a parent’s offspring, and that is likely to have originated and/or be currently maintained for this function. How parental care evolves and which sex should care for the offspring are central questions in evolutionary biology. The theoretical bases to address these questions were proposed almost 45 years ago, but recent models have challenged classical foundations and proposed new hypotheses. An in-depth account of these models is beyond the scope of this chapter. Updated numbers for the taxonomic distribution and frequency of the different forms of post-ovipositional parental care in insects are provided. These numbers are used to construct hypotheses on the transitions between systems of care, the selective pressures that favoured the origin of care, and the evolution of male care and biparental care. Finally, gaps in our knowledge and indicate possible directions for future studies are empahsized.

This chapter examines the early formation of the culture of dependent nationalism, a form of historical consciousness that fosters a pragmatic and immoral realism and which justifies private benefits gained from the regretful present with a language of evolutionary transition. It conceives of dependency as a specific condition that emerged in Latin America, when the national economies of those countries were reoriented to the United States and the United States became the guardian of their national credit, a process that began to take shape in the 1870s but which only became a palpable reality by the late 1890s. The chapter also explores the culture of dependency by way of its “chronotopes,” that is, through the ways in which the nation was figured in space and time. Two competing figures are described that emerged in this period. One of these took shape in a new field of international relations, whereas the other was a product of emerging grassroots transnational organization. These two competing spatiotemporal frameworks are a defining characteristic of dependency as a form of historical consciousness.