Although the role of morphology in evolutionary theory remains a subject of debate, assessing the contributions of morphological investigation to evolutionary developmental biology (Evo-devo) is a more circumscribed issue of direct relevance to ongoing research. Historical studies of morphologically oriented researchers and the formation of the Modern Synthesis in the Anglo-American context identify a recurring theme: the synthetic theory of evolution did not capture multiple levels of biological organization. When this feature is incorporated into a philosophical framework for explaining the (...) origin of evolutionary innovations and novelties (a core domain of inquiry in Evo-devo) two specific roles for morphology can be described: (1) the conceptualization and operational identification of the targets of explanation; and (2) the elucidation of causal interactions at higher levels of organization during ontogeny and through evolutionary time. These roles are critical components of any adequate explanation of innovation and novelty though not exhaustive of the parts played by morphology in evolutionary investigation. They also invite reflection on what counts as an evolutionary cause in contemporary evolutionary biology. (shrink)

This chapter describes the theoretical implications of Extended Synthesis and addresses the methodological options available for determining aspects of theoretical structure. It uses a “bottom-up” approach focused on evolutionary theory in particular, as opposed to a “top-down” strategy that attempts to characterize the structure of all scientific theories. The chapter shows that there are multiple stable components contained within a broad representation of evolutionary theory. It suggests that the philosophical analysis offered in the chapter regarding the structure of evolutionary theory (...) assists attempts to recover coherence through the vehicle of an Extended Synthesis. (shrink)

Exploring history pertinent to evolutionary developmental biology (hereafter, Evo-devo) is an exciting prospect given its current status as a cutting-edge field of research. The first and obvious question concerns where to begin searching for materials and sources. Since this new discipline adopts a moniker that intentionally juxtaposes ‘evolution’ and development’, individuals, disciplines, and institutional contexts relevant to the history of evolutionary studies and investigations of ontogeny prompt themselves. Each of these topics has received attention from historians and thus there is (...) both primary and secondary material from which to draw. For example, many historians have documented the historical trajectories of genetics and embryology, their split, and various relations (or lack thereof), especially in the first three decades of the 20th century. (shrink)

This paper focuses on abstraction as a mode of reasoning that facilitates a productive relationship between philosophy and science. Using examples from evolutionary developmental biology, I argue that there are two areas where abstraction can be relevant to science: reasoning explication and problem clarification. The value of abstraction is characterized in terms of methodology (modeling or data gathering) and epistemology (explanatory evaluation or data interpretation).

The 1981 Dahlem conference was a catalyst for contemporary evolutionary developmental biology (Evo-devo). This introductory chapter rehearses some of the details of the history surrounding the original conference and its associated edited volume, explicates the philosophical problem of conceptual change that provided the rationale for a workshop devoted to evaluating the epistemic revisions and transformations that occurred in the interim, explores conceptual change with respect to the concept of evolutionary novelty, and highlights some of the themes and patterns in the (...) different contributions to the present volume, Conceptual Change in Biology: Scientific and Philosophical Perspectives on Evolution and Development. (shrink)

Developmental biology is the science of explaining how a variety of interacting processes generate the heterogeneous shapes, size, and structural features of an organism as it develops rom embryo to adult, or more generally throughout its life cycle (Love, 2008b; Minelli, 2011a). Although it is commonplace in philosophy to associate sciences with theories such that the individuation of a science is dependent on a constitutive theory or group of models, it is uncommon to find presentations of developmental biology making reference (...) to a theory or theories of development. For example, in the third edition of Essential Developmental Biology (Slack, 2013), three families of approaches are described (developmental genetics, experimental embryology, and molecular and cell biology), and the appendix contains a catalogue of ‘key molecular components’ (genes, transcription factor, families, inducing factor families, cytoskeleton, cell adhesion molecules, and extracellular matrix components); however, no standard theory or group of models provides a theoretical scaffolding to the book nor is any mentioned. (shrink)

Developmental biology is the science of explaining how a variety of interacting processes generate an organism’s heterogeneous shapes, size, and structural features that arise on the trajectory from embryo to adult, or more generally throughout a life cycle. It represents an exemplary area of contemporary experimental biology that focuses on phenomena that have puzzled natural philosophers and scientists for more than two millennia.

Comprehending the origin of marine invertebrate larvae remains a key domain of research for evolutionary biologists, including the repeated origin of direct developmental modes in echinoids. In order to address the latter question, we surveyed existing evidence on relationships of homology between the ectoderm territories of two closely related sea urchin species in the genus Heliocidaris that differ in their developmental mode. Additionally, we explored a recently articulated idea about homology called ‘organizational homology’ (Muller 2003. In: Muller GB, Newman SA, (...) editors. Origination of organismal form: beyond the gene in developmental and evolutionary biology. Cambridge, MA: A Bradford Book, The MIT Press. p 51–69. ) in the context of this specific empirical case study. Applying the perspective of organizational homology to our experimental system of congeneric echinoids has led us to a new hypothesis concerning the ectoderm evolution in these species. The extravestibular ectoderm of the direct developer Heliocidaris erythrogramma is a novel developmental territory that arose as a fusion of the oral and aboral ectoderm territories found in indirect developing echinoids such as Heliocidaris tuberculata. This hypothesis instantiates a theoretical principle concerning the origin of developmental modules, ‘integration’, which has been neglected because the opposite theoretical principle, ‘parcellation’, is more readily observable in events such as gene duplication and divergence (Wagner 1996. Am Zool 36:36–43). J. Exp. Zool. (Mol. Dev. Evol.) 306B:18– 34, 2006. (shrink)

Although sciences are often conceptualized in terms of theory confirmation and hypothesis testing, an equally important dimension of scientific reasoning is the structure of problems that guide inquiry. This problem structure is evident in several concepts central to evolutionary developmental biology (Evo-devo)—constraints, modularity, evolvability, and novelty. Because problems play an important role in biological practice, they should be included in biological pedagogy, especially when treating the issue of scientific controversy. A key feature of resolving controversy is synthesizing methodologies from different (...) biological disciplines to generate empirically adequate explanations. Concentrating on problem structure illuminates this interdisciplinarity in a way that is often ignored when science is taught only from the perspective of theory or hypothesis. These philosophical considerations can assist life science educators in their continuing quest to teach biology to the next generation. -/- . (shrink)

Overview The evolution of multicellularity raises questions regarding genomic and developmental commonalities and discordances, selective advantages and disadvantages, physical determinants of development, and the origins of morphological novelties. It also represents a change in the definition of individuality, because a new organism emerges from interactions among single cells. This volume considers these and other questions, with contributions that explore the origins and consequences of the evolution of multicellularity, addressing a range of topics, organisms, and experimental protocols. Each section focuses on (...) selected topics or particular lineages that present a significant insight or challenge. The contributors consider the fossil record of the paleontological circumstances in which animal multicellularity evolved; cooptation, recurrent patterns, modularity, and plausible pathways for multicellular evolution in plants; theoretical approaches to the amoebozoa and fungi (cellular slime molds having long provided a robust model system for exploring the evolution of multicellularity), plants, and animals; genomic toolkits of metazoan multicellularity; and philosophical aspects of the meaning of individuality in light of multicellular evolution. Contributors Maja Adamska, Argyris Arnellos, Juan A. Arias, Eugenio Azpeitia, Mariana Benítez, Adriano Bonforti, John Tyler Bonner, Peter L. Conlin, A. Keith Dunker, Salva Duran-Nebreda, Ana E. Escalante, Valeria Hernández-Hernández, Kunihiko Kaneko, Andrew H. Knoll, Stephan G. König, Daniel J. G. Lahr, Ottoline Leyser, Alan C. Love, Raul Montañez, Emilio Mora van Cauwelaert, Alvaro Moreno, Vidyanand Nanjundiah, Aurora M. Nedelcu, Stuart A. Newman, Karl J. Niklas, William C. Ratcliff, Iñaki Ruiz-Trillo, Ricard Solé . (shrink)

Scientists exhibit different styles in their reasoning about the natural world (e.g., experimental, historical, or statistical). These styles have been characterized, categorized, and combined in many ways throughout the history of science.

The larval arms of echinoid plutei are used for locomotion and feeding. They are composed of internal calcite skeletal rods covered by an ectoderm layer bearing a ciliary band. Skeletogenesis includes an autonomous molecular differentiation program in primary mesenchyme cells (PMCs), initiated when PMCs leave the vegetal plate for the blastocoel, and a patterning of the differentiated skeletal units that requires molecular cues from the overlaying ectoderm. The arms represent a larval feature that arose in the echinoid lineage during the (...) Paleozoic and offers a subject for the study of gene co-option in the evolution of novel larval features. We isolated new molecular markers in two closely related but differently developing species, Heliocidaris tuberculata and Heliocidaris erythrogramma. We report the expression of a larval arm-associated ectoderm gene tetraspanin, as well as two new PMC markers, advillin and carbonic anhydrase. Tetraspanin localizes to the animal half of blastula stage H. tuberculata and then undergoes a restriction into the putative oral ectoderm and future location of the postoral arms, where it continues to be expressed at the leading edge of both the postoral and anterolateral arms. In H. erythrogramma, its expression initiates in the animal half of blastulae and expands over the entire ectoderm from gastrulation onward. Advillin and carbonic anhydrase are upregulated in the PMCs postgastrulation and localized to the leading edge of the growing larval arms of H. tuberculata but do not exhibit coordinated expression in H. erythrogramma larvae. The tight spatiotemporal regulation of these genes in H. tuberculata along with other ontogenetic and phylogenetic evidence suggest that pluteus arms are novel larval organs, distinguishable from the processes of skeletogenesis per se. The dissociation of expression control in H. erythrogramma suggest that coordinate gene expression in H. tuberculata evolved as part of the evolution of pluteus arms, and is not required for larval or adult development. (shrink)

The star-nosed mole is aptly named. Its distinctive snout consists of 22 tendrils ringing a pair of nostrils and, from some angles, the entire setup resembles a misshapen star. The tendrils are fleshy and look a bit like fingers, and, like fingers, they have a certain dexterity. But why? Why does the mole have such a singular appendage as opposed to something more ordinary? What is the function or purpose of this bizarre structure? From the dedicated work of Ken Catania, (...) of Vanderbilt University, and colleagues, it appears that the appendage facilitates rapid handling of small prey items, making it advantageous for an organism whose diet consists of tiny invertebrates. We might therefore hazard that this feature arose evolutionarily because it conferred this benefit. But the matter is difficult to resolve, because current utility does not permit a straightforward inference of a reason for existence. -/- A correction has been published: BioScience, Volume 72, Issue 7, July 2022, Page 708. (shrink)

The origin of marine invertebrate larvae has been an area of controversy in developmental evolution for over a century. Here, we address the question of whether a pelagic “larval” or benthic “adult” morphology originated first in metazoan lineages by testing the hypothesis that particular gene co-option patterns will be associated with the origin of feeding, indirect developing larval forms. Empirical evidence bearing on this hypothesis is derivable from gene expression studies of the sea urchin larval gut of two closely related (...) but differently developing congenerics, Heliocidaris tuberculata (feeding indirect-developing larva) and H. erythrogramma (nonfeeding direct developer), given two subsidiary hypotheses. (1) If larval gut gene expression in H. tuberculata was co-opted from an ancestral adult expression pattern, then the gut expression pattern will remain in adult H. erythrogramma despite its direct development. (2) Genes expressed in the larval gut of H. tuberculata will not have a coordinated expression pattern in H. erythrogramma larvae due to loss of a functional gut. Five structural genes expressed in the invaginating archenteron of H. tuberculata during gastrulation exhibit substantially different expression patterns in H. erythrogramma with only one remaining endoderm specific. Expression of these genes in the adult of H. erythrogramma and larval gut of H. tuberculata, but not in H. erythrogramma larval endoderm, supports the hypothesis that they first played roles in the formation of adult structures and were subsequently recruited into larval ontogeny during the origin and evolution of feeding planktotrophic deuterostome larvae. (shrink)

The origination of novel structures has long been an intriguing topic for biologists. Over the past few decades it has served as a central theme in evolutionary developmental biology. Yet, definitions of evolutionary innovation and novelty are frequently debated and there remains disagreement about what kinds of causal factors best explain the origin of qualitatively new variation in the history of life. Here we examine aspects of these debates, survey three empirical case studies, and reflect on directions for future inquiry (...) that will advance research into the developmental evolution of novel structures. (shrink)

An overlooked feature of Darwin’s work is his use of “imaginary illustrations” to show that natural selection is competent to produce adaptive, evolutionary change. When set in the context of Darwin’s methodology, these thought.

Judgments of plausibility involve appearance of the truth or reasonableness, which is always a function of background knowledge. What anyone will countenance is conditioned by what they already know (or think they know). Marc Kirschner (professor of systems biology at Harvard) and John Gerhart (professor of molecular and cell biology at the University of California—Berkeley) aim to show that molecular, cellular, and developmental processes relevant to the generation of phenotypic variation in anatomy, physiology, and behavior demonstrate how evolutionary processes, especially (...) the origins of novelty, are plausible. The outstanding question for Kirschner and Gerhart concerns not the modification of structures but their origination—a question unanswered by the theoretical framework of the modern synthesis. (shrink)

Book review of "The Nature of Scientific Thinking: on Interpretation, Explanation and Understanding" by J. Faye. The nature of scientific explanation is a central topic of interest to philosophers but the literature has metamorphosed from a coherent body of key papers and examples into narrow and specialized discussions in different scientific disciplines.

From Arabidopsis and Antirrhinum to Arabia and Antioch: a review of cells to civilizations: the principles of change that shape life -/- Cells to Civilizations: The Principles of Change That Shape Life, Coen, E. 2012. Princeton University Press, Princeton, NJ. 312 pp. ISBN 978-0-691-14967-7.

Book review of "Causality: Philosophical Theory Meets Scientific Practice" by P. Illari and F. Russo,.

Essay review of David Arnold, "The Tropics and the Traveling Gaze: India, Landscape, and Science, 1800-1856" (Seattle: University of Washington Press, 2006), xiv + 298 pp., illus.

Reduction and reductionism have been central philosophical topics in analytic philosophy of science for more than six decades. Together they encompass a diversity of issues from metaphysics and epistemology. This article provides an introduction to the topic that illuminates how contemporary epistemological discussions took their shape historically and limns the contours of concrete cases of reduction in specific natural sciences. The unity of science and the impulse to accomplish compositional reduction in accord with a layer-cake vision of the sciences, the (...) seminal contributions of Ernest Nagel on theory reduction and how they strongly conditioned subsequent philosophical discussions, and the detailed issues pertaining to different accounts of reduction that arise in both physical and biological science (e.g., limit-case and part-whole reduction in physics, the difference-making principle in genetics, and mechanisms in molecular biology) are explored. The conclusion argues that the epistemological heterogeneity and patchwork organization of the natural sciences encourages a pluralist stance about reduction. (shrink)

The concept of evolvability—the capacity of a population to produce and maintain evolutionarily relevant variation—has become increasingly prominent in evolutionary biology. Paleontology has a long history of investigating questions of evolvability, but paleontological thinking has tended to neglect recent discussions, because many tools used in the current evolvability literature are challenging to apply to the fossil record. The fundamental difficulty is how to disentangle whether the causes of evolutionary patterns arise from variational properties of traits or lineages rather than being (...) due to selection and ecological success. Despite these obstacles, the fossil record offers unique and growing sources of data that capture evolutionary patterns of sustained duration and significance otherwise inaccessible to evolutionary biologists. Additionally, there exist a variety of strategic possibilities for combining prominent neontological approaches to evolvability with those from paleontology. We illustrate three of these possibilities with quantitative genetics, evolutionary developmental biology, and phylogenetic models of macroevolution. In conclusion, we provide a methodological schema that focuses on the conceptualization, measurement, and testing of hypotheses to motivate and provide guidance for future empirical and theoretical studies of evolvability in the fossil record. (shrink)

Inquiry is an important learning strategy, even for students who cannot or do not perform actual experiments. The authors describe two activities, other than experimentation, that they used in introductory biology learning groups to emphasize inquiry abilities. They also provide recommendations for creating additional inquiry activities.

Conceptual features differ in how mentally tranformable they are. A robin that does not eat is harder to imagine than a robin that does not chirp. We argue that features are immutable to the extent that they are central in a network of dependency relations. The immutability of a feature reflects how much the internal structure of a concept depends on that feature; i.e., how much the feature contributes to the concept's coherence. Complementarily, mutability reflects the aspects in which a (...) concept is flexible. We show that features can be reliably ordered according to their mutability using tasks that require people to conceive of objects missing a feature, and that mutability (conceptual centrality) can be distinguished from category centrality and from diagnosticity and salience. We test a model of mutability based on asymmetric, unlabeled, pairwise dependency relations. With no free parameters, the model provides reasonable fits to data. Qualitative tests of the model show that mutability judgments are unaffected by the type of dependency relation and that dependency structure influences judgments of variability. (shrink)

With the large number of clinical practice guidelines available, there is an increasing need for a comprehensive unified model for acute ischemic stroke treatment to assist in clinical decision making. We present a unified treatment model derived through review of existing clinical practice guidelines, meta-analyses, and clinical trials. Using logic from the treatment model, a Bayesian belief network was defined and fitted to data from our institution's observational quality improvement database for acute stroke patients. The resulting network validates known relationships (...) between variables, treatment decisions and outcomes, and enables the exploration of new correlative relationships not defined in current guidelines. © 2013 IMIA and IOS Press. (shrink)

It is a common complaint that antireductionist arguments are primarily negative. Here I describe an alternative nonreductionist epistemology based on considerations taken from multidisciplinary research in biology. The core of this framework consists in seeing investigation as coordinated around sets of problems (problem agendas) that have associated criteria of explanatory adequacy. These ideas are developed in a case study, the explanation of evolutionary innovations and novelties, which demonstrates the applicability and fruitfulness of this nonreductionist epistemological perspective. This account also bears (...) on questions of conceptual change and theory structure in philosophy of science. †To contact the author, please write to: Department of Philosophy, University of Minnesota, 831 Heller Hall, 271 19th Ave. S., Minneapolis, MN 55455; e‐mail: [email protected]. (shrink)

The goal of this paper is to encourage a reconfiguration of the discussion about typology in biology away from the metaphysics of essentialism and toward the epistemology of classifying natural phenomena for the purposes of empirical inquiry. First, I briefly review arguments concerning ‘typological thinking’, essentialism, species, and natural kinds, highlighting their predominantly metaphysical nature. Second, I use a distinction between the aims, strategies, and tactics of science to suggest how a shift from metaphysics to epistemology might be accomplished. Typological (...) thinking can be understood as a scientific tactic that involves representing natural phenomena using idealizations and approximations, which facilitates explanation, investigation, and theorizing via abstraction and generalization. Third, a variety of typologies from different areas of biology are introduced to emphasize the diversity of this representational reasoning. One particular example is used to examine how there can be epistemological conflict between typology and evolutionary analysis. This demonstrates that alternative strategies of typological thinking arise due to the divergent explanatory goals of researchers working in different disciplines with disparate methodologies. I conclude with several research questions that emerge from an epistemological reconfiguration of typology. (shrink)

“Functional homology” appears regularly in different areas of biological research and yet it is apparently a contradiction in terms—homology concerns identity of structure regardless of form and function. I argue that despite this conceptual tension there is a legitimate conception of ‘homology of function’, which can be recovered by utilizing a distinction from pre-Darwinian physiology (use versus activity) to identify an appropriate meaning of ‘function’. This account is directly applicable to molecular developmental biology and shares a connection to the theme (...) of hierarchy in homology. I situate ‘homology of function’ within existing definitions and criteria for structural assessments of homology, and introduce a criterion of ‘organization’ for judging function homologues, which focuses on hierarchically interconnected interdependencies (similar to relative position and connection for skeletal elements in structural homology). This analysis of biological concepts has at least three broad philosophical consequences: (1) it provides the grounds for the study of behavior and psychological categories as homologues; (2) it demonstrates that philosophers who take selected effect function as primary effectively ignore large portions of comparative, structural, and experimental research, thereby misconstruing biological reasoning and knowledge; and, (3) it underwrites causal generalizations, which illuminates inferences made from model organisms in experimental biology. (shrink)

One foundational question in contemporarybiology is how to `rejoin evolution anddevelopment. The emerging research program(evolutionary developmental biology or`evo-devo) requires a meshing of disciplines,concepts, and explanations that have beendeveloped largely in independence over the pastcentury. In the attempt to comprehend thepresent separation between evolution anddevelopment much attention has been paid to thesplit between genetics and embryology in theearly part of the 20th century with itscodification in the exclusion of embryologyfrom the Modern Synthesis. This encourages acharacterization of evolutionary developmentalbiology as the marriage (...) of evolutionary theoryand embryology via developmental genetics. Butthere remains a largely untold story about thesignificance of morphology and comparativeanatomy (also minimized in the ModernSynthesis). Functional and evolutionarymorphology are critical for understanding thedevelopment of a concept central toevolutionary developmental biology,evolutionary innovation. Highlighting thediscipline of morphology and the concepts ofinnovation and novelty provides an alternativeway of conceptualizing the `evo and the `devoto be synthesized. (shrink)

Causal relations among components and activities are intentionally misrepresented in mechanistic explanations found routinely across the life sciences. Since several mechanists explicitly advocate accurately representing factors that make a difference to the outcome, these idealizations conflict with the stated rationale for mechanistic explanation. We argue that these idealizations signal an overlooked feature of reasoning in molecular and cell biology—mechanistic explanations do not occur in isolation—and suggest that explanatory practices within the mechanistic tradition share commonalities with model-based approaches prevalent in population (...) biology. (shrink)

Many philosophers of biology have embraced a version of pluralism in response to the failure of theory reduction but overlook how concepts, methods, and explanatory resources are in fact coordinated, such as in interdisciplinary research where the aim is to integrate different strands into an articulated whole. This is observable for the origin of evolutionary novelty—a complex problem that requires a synthesis of intellectual resources from different fields to arrive at robust answers to multiple allied questions. It is an apt (...) locus for exploring new dimensions of explanatory integration because it necessitates coordination among historical and experimental disciplines . These coordination issues are widespread for the origin of novel morphologies observed in the Cambrian Explosion. Despite an explicit commitment to an integrated, interdisciplinary explanation, some potential disciplinary contributors are excluded. Notable among these exclusions is the physics of ontogeny. We argue that two different dimensions of integration—data and standards—have been insufficiently distinguished. This distinction accounts for why physics-based explanatory contributions to the origin of novelty have been resisted: they do not integrate certain types of data and differ in how they conceptualize the standard of uniformitarianism in historical, causal explanations. Our analysis of these different dimensions of integration contributes to the development of more adequate and integrated explanatory frameworks. (shrink)

Although natural philosophers have long been interested in individuality, it has been of interest to contemporary philosophers of biology because of its role in different aspects of evolutionary biology. These debates include whether species are individuals or classes, what counts as a unit of selection, and how transitions in individuality occur evolutionarily. Philosophical analyses are often conducted in terms of metaphysics (“what is an individual?”), rather than epistemology (“how can and do researchers conceptualize individuals so as to address some of (...) their scientific goals?”). We review several philosophical distinctions in order to shift attention from metaphysics to epistemology. Many controversies involve epistemological differences rather than metaphysical disagreement. This implies that a pluralist stance about individuality in biology is warranted and has metaphysical consequences because the pluralism emerges from the diversity of scientific interests that investigate the complexity of living phenomena. (shrink)

Every scientist chooses a preferred level of analysis and this choice shapes the research program, even determining what counts as evidence. This contribution revisits Marr's three levels of analysis and evaluates the prospect of making progress at each individual level. After reviewing limitations of theorizing within a level, two strategies for integration across levels are considered. One is top–down in that it attempts to build a bridge from the computational to algorithmic level. Limitations of this approach include insufficient theoretical constraint (...) at the computation level to provide a foundation for integration, and that people are suboptimal for reasons other than capacity limitations. Instead, an inside-out approach is forwarded in which all three levels of analysis are integrated via the algorithmic level. This approach maximally leverages mutual data constraints at all levels. For example, algorithmic models can be used to interpret brain imaging data, and brain imaging data can be used to select among competing models. Examples of this approach to integration are provided. This merging of levels raises questions about the relevance of Marr's tripartite view. (shrink)

Idealization is a reasoning strategy that biologists use to describe, model and explain that purposefully departs from features known to be present in nature. Similar to other strategies of scientific reasoning, idealization combines distinctive strengths alongside of latent weaknesses. The study of ontogeny in model organisms is usually executed by establishing a set of normal stages for embryonic development, which enables researchers in different laboratory contexts to have standardized comparisons of experimental results. Normal stages are a form of idealization because (...) they intentionally ignore known variation in development, including variation associated with phenotypic plasticity (e.g. via strict control of environmental variables). This is a tension between the phenomenon of plasticity and the practice of staging that has consequences for evolutionary developmental investigation because variation is conceptually removed as a part of rendering model organisms experimentally tractable. Two compensatory tactics for mitigating these consequences are discussed: employing a diversity of model organisms and adopting alternative periodizations. (shrink)