Ideas perhaps rightly rejected in the past due to a lack of supporting evidence must now be re-evaluated in the light of contemporary knowledge. Advances at the interface of ecology, behaviour and culture have shown that populations of organisms are not merely passively exposed to natural selection but are actively involved in the formation of those environments that constitute the selective conditions for later populations. The supposed randomness of genetic variation further contributed to this view. Although the EES recognizes the fundaments of the classical MS theory, it differs in its interpretation of the role of some of its elements and integrates new components, such as constructive processes of development, multiple inheritance mechanisms, niche reciprocity, as well as behavioural and cultural elements (on which this overview did not dwell much, but see other contributions to this issue). It is unavoidable to notice that an integration of these concepts means not a simple add-on of a few peripheral notions to the MS model without any effects on its core logic. The extended evolutionary synthesis (EES) is new a way to think about and understand evolutionary phenomena that differs from the conception that has dominated evolutionary thinking since the 1930s (i.e., the modern synthesis). All these features stimulate research into new areas of evolutionary biology. Since the last major theoretical integration in evolutionary biology—the modern synthesis (MS) of the 1940s—the biosciences have made significant advances. Feedback interactions among different levels of organization in developmental systems. Einstein A. If the explanation would stop here, no controversy would exist. The question, for instance, of how complex phenotypic organizations arise in evolution is sidestepped by the population theoretical account, as is the reciprocal influence of these features of higher levels of organization on the evolutionary process. Again we are confronted with a classical criticism that stood at the centre of multiple debates in the past [42], but the issue is as unresolved as ever. Now that whole genomes can be studied, we have learned that in the course of evolution significant portions of the genome have been duplicated, deleted or co-opted into new functions [40]. Why an extended evolutionary synthesis is necess… This is an exciting period in evolutionary biology. In the MS, at least in its bare bones interpretations, organismal shape and structure were regarded entirely as products of external selection, and the directionality of evolutionary change was supposed to result from natural selection alone. Unable to load your collection due to an error, Unable to load your delegates due to an error. A renewed and extended theoretical synthesis, advocated by several authors in this issue, aims to unite pertinent concepts that emerge from the novel fields with elements of the standard theory. The predictions that follow from the MS framework continue to be based on these prerequisites and ignore all predictions derived from alternative models. A century ago, it was noted in the domain of physics that ‘concepts that have proven useful in ordering things easily achieve such an authority over us that we forget their earthly origins and accept them as unalterable givens. This represents a shift from a programmed to a constructive role of developmental processes in evolution. As philosopher Karl Popper has noticed, the current evolutionary theory is a theory of genes, and we still lack a theory of forms. Recently, some researchers have argued that a new extended evolutionary synthesis (EES) is necessary [4] in order to account for specific phenomena. A renewed and extended theoretical synthesis, advocated by several authors in this issue, aims to unite pertinent concepts that emerge from the novel fields with elements of the standard theory. What is important is that a different theory structure is necessary to accommodate the new concepts that are in everyday use and have become part of the current toolkit of evolutionary biology. Thus, the properties of genetic change are found to be quite different from the assumptions made by the founders of the MS, when continued random substitution of individual alleles was the reigning understanding. Why an extended evolutionary synthesis is necessary. What is the extended evolutionary synthesis? Some of these results are in agreement with the standard theory and others reveal different properties of the evolutionary process. Evolutionary biology, as practised today, does not represent a single coherent approach but includes sets of different topics and research programmes. Hence, it will be useful to characterize some of the differences that exist between the MS theory and proposed alternatives. Quite evidently, the MS theory has become too narrow in several regards, but this does not mean that all its elements have been invalidated. Its dynamics plays out before the background of developmental plasticity and evolving gene regulation, but it also includes the self-organizing, physics-dependent and environmentally mediated properties of development. None of these contentions are unscientific, all rest firmly on evolutionary principles and all are backed by substantial empirical evidence. A major reason why an extended evolutionary synthesis, or as some call it ‘The Third Way’, is gaining ground among secular scientists is that (in one evolutionist’s own words) “all the central assumptions of the Modern Synthesis (often called Neo-Darwinism) have been disproved”. Clipboard, Search History, and several other advanced features are temporarily unavailable. Jablonka E, Lamb MJ. Interest in multilevel selection theory has resurged in connection to work on the major transitions in evolution and definitions of biological causality [91]. This is a normal process of scientific advancement and not a heretical undertaking as it is sometimes perceived to be. No, all is well, What was really synthesized during the evolutionary synthesis? Privacy, Help Schematic depiction of defining theory components and relations in (a) the MS (after Odling-Smee et al. In parallel, a number of philosophical standpoints have emerged in an attempt to clarify what exactly is represented by the EES. The novelty of the EES and the differences with the MS theory become most apparent in the predictions that derive from the EES framework, both with regard to short-term and long-term effects of organismal evolution. When mutation of individual genes or even smaller entities of DNA is taken as the predominant source of variation, it seemed inevitable that phenotypic modifications should be small, because larger changes were deemed to be disruptive and unlikely to produce adaptive outcomes. Prevention and treatment information (HHS). Before natural selection can act, the developmental system harbours tendencies towards certain solutions, a property that has been called developmental bias [57,58]. Moreover, critics infallibly call for further empirical evidence, giving the impression that the EES is an unfounded theoretical exercise that still awaits confirmation. In addition, the EES accepts behavioural, ecological and cultural transmission as well as the interactions between the different modes of transgenerational inheritance. 2021 Jan 12;118(2):e2006564118. The empirical basis and key concern of the population genetic approach is the measurement of trait variability in populations, and its intended explananda are adaptive variation, speciation and calculations of fitness. Modern synthesis. Major differences are indicated by different colours. Some of these results are in agreement with the standard theory and others reveal different properties of the evolutionary process. The extended evolutionary synthesis consists of a set of theoretical concepts more comprehensive than the earlier modern synthesis of evolutionary biology that took place between 1918 and 1942. Irrespective of whether they are perturbed by selectional, mutational or experimental intervention, developmental systems exhibit emergent behaviours and generate nonlinear effects, i.e. Yes, urgently, Extended evolution: a conceptual framework for integrating regulatory networks and niche construction, The extended evolutionary synthesis: its structure, assumptions and predictions, Evolutionary developmental biology offers a significant challenge to Neo-Darwinian paradigm, Transgenerational epigenetic inheritance: prevalence, mechanisms, and implications for the study of heredity and evolution, Physiology is rocking the foundations of evolutionary biology, A 21st century view of evolution: genome system architecture, repetitive DNA, and natural genetic engineering, Evolutionary consequences of niche construction and their implications for ecology, The frailty of adaptive hypotheses for the origins of organismal complexity, Rethinking gene regulatory networks in light of alternative splicing, intrinsically disordered protein domains, and post-translational modifications, Phenotypic novelty in evo-devo: the distinction between continuous and discontinuous variation and its importance in evolutionary theory, Evolutionary biology and the emergence of agriculture: the value of co-opted models of evolution in the study of culture change, Modes of variation and their implications for an extended evolutionary synthesis, The extended synthesis: the law of the conditions of existence. Together, they constitute the kernel of an organizational theory component that sets the EES apart from the MS. Another distinctive feature of the EES is causal reciprocity. Major differences are indicated by different colours. First, the kind of selectable phenotypic variation that can be produced by a developmental system of a given type is neither infinite nor random. Plasticity has also been linked to the ubiquitous phenomenon of homoplasy [83] and to rapid divergence of phylogenetic lineages [21]. Evolution in four dimensions. Would you like email updates of new search results? As philosopher Karl Popper has noticed, the current evolutionary theory is a theory of genes, and we still lack a theory of forms. Whatever lip service is paid to taking into account other factors than those traditionally accepted, we find that the theory, as presented in extant writings, concentrates on a limited set of evolutionary explananda, excluding the majority of those mentioned among the explanatory goals above. Published August 26, 2017. The kind of systems biology capable of doing this is not the ubiquitous ‘-omics’ blossoming today, but the theoretical framework that deals with the study of systems properties of organisms and their interactions across levels of organization, from molecules to populations of organisms, including physiological, behavioural and cultural factors. Epub 2018 Nov 16. Numerous authors have challenged the pervasiveness of natural selection as a unique ‘force’ of evolution, whereas others have questioned whether the individual is the sole and appropriate ‘target’ of selection or whether other levels of selection at supra- and infra-individual levels also need to be included in selectionist scenarios [42–44]. Rather, selectable variation is both constrained [55] and facilitated [56] by development. Initial approaches to unify genetic and non-genetic heritability, as well as their relative contributions and mutual interactions, have successfully established quantitative models of inclusive inheritance [9]. The problem of phenotypic complexity thus becomes (in)elegantly bypassed. It is important to take into consideration the fact that contemporary scientific inquiry has a new twist, the Extended Evolutionary Synthesis (EES), in the tale it provides about the origin of our species. The proposition of uniquely genetic inheritance has been falsified multiple times [3], but the gene-centric position remains constitutive of the MS. It was actually built by expanding on the conceptual foundations laid out by its predecessors, Darwinism and neo‐Darwinism. As can be noted from the listed principles, current evolutionary theory is predominantly oriented towards a genetic explanation of variation, and, except for some minor semantic modifications, this has not changed over the past seven or eight decades. Early in life effects and heredity: reconciling neo-Darwinism with neo-Lamarckism under the banner of the inclusive evolutionary synthesis. Are all features of biological organisms necessarily the result of natural selection, and is it the only factor in the evolutionary process that provides directionality to organismal change? -, Pigliucci M. 2007. Morphological templates that result from the mobilization of physical forces are seen to represent basic organizing themes in animals [68] and plants [69] that become integrated through a hierarchization of regulatory networks and fixated as patterns of phenotypic construction [70]. Thus, they come to be stamped as “necessities of thought”, “a priori givens”, etc. Schematic depiction of defining theory components and relations in (a) the MS (after Odling-Smee et al. Equally encompassing effects of niche construction have been demonstrated in plants [21,69,100]. Also, here we beg to differ. 2018;45(1):1-14. doi: 10.1007/s11692-017-9431-x. In response, Wray et al. Epub 2017 Aug 18. The population context of development is mostly provided by the study of developmental plasticity, a component of phenotypic plasticity. A well-established paradigm that has its roots in a major theoretical integration that took place approximately eight decades ago, traditionally labelled the modern synthesis (MS) or Synthetic Theory, still dominates evolutionary thought today. Feedback interactions among different levels…, Feedback interactions among different levels of organization in developmental systems. It continues to see variation, differential reproduction, heredity, natural selection, drift, etc., as necessary components of evolution, but it differs in how these factors are conceptualized. Hence, the micro–macro distinction only serves to obscure the important issues that emerge from the current challenges to the standard theory. Examples of autonomous…, Schematic depiction of defining theory components and relations in ( a ) the…, National Library of Medicine Evolutionary biology finds itself in a similar situation today. (10.1111/j.1558-5646.2007.00246.x) Haldane, Ernst Mayr, and Theodosius Dobzhansky. The actual modern synthesis is a collaboration of a large body of work from such celebrated scientists as J.B.S. The resulting theoretical framework differs from the latter in its core logic and predictive capacities. Particular forms of phenotypic change are taken as the result of internal generative conditions rather than external pruning. Whereas different forms of adaptationism can be discerned, for instance in the British and the American research traditions [30], the notion most frequently encountered is still that of a collection of features that make up the organism, each one individually adapted to performing a function in the way best suited for the organism's survival, a picture that has been described as ‘bundles of discrete adaptations.’ This view was neither eliminated by Dobzhansky's alternative view, in which he interpreted populations as states of relative adaptedness [30], nor by the demonstration of the frequent occurrence of non-adaptive traits. The most important predictions concern the following: (i) the generation of heritable phenotypic variation (variation will be systematically biased and facilitated by the generative features of development); (ii) the origin of phenotypic novelty (novelties are due to emergent and self-organizing properties of developmental systems); (iii) the sequence of genetic and phenotypic change (emergent phenotypic structures can be captured and stabilized by evolving gene regulatory circuitry and assume fitness subsequently); (iv) inheritance (in addition to genetic inheritance, adaptive variants are propagated by non-genetic inheritance, learning and cultural transmission, as well as by repeated environmental induction); (v) tempo of evolution (periods of rapid phenotypic evolution can alternate with periods of slow and continuous change); (vi) environmental induction (phenotypic variation can be environmentally induced in multiple individuals simultaneously); (vii) organismal activity (niche construction effectuates environmental changes that enhance the fitness of the constructors and their descendants; (viii) natural selection (the primary evolutionary effect of natural selection is not to eliminate the unfit but to release generative potential). Although non-genetic inheritance is sometimes dismissed as representing exclusively proximate mechanisms whose ultimate (evolutionary) functions do not run counter to the MS [97], the shortcomings of such arguments and of the widespread proximate–ultimate distinction in general have been convincingly demonstrated [98]. Already in the late 1970s, Gould & Lewontin [41] described the adherence to pervasive adaptationism as an ‘old habit,’ but despite extensive learned discussions of the subject that habit has not receded. A suite of new concepts emerges from evo-devo, a field of research that arose in the early 1980s from a discontent with the exclusion of developmental biology from evolutionary theory [50–53]. Figure 1. Correction to 'Why an extended evolutionary synthesis is necessary'. The EES was proposed as a theoretical framework that takes account of the plurality of factors and causal relations in evolutionary processes [15,49]. extended evolutionary synthesis (EES). 8, 943–949. Even though it never constituted an encompassing formal synthesis [34], this movement had brought together the basic neo-Darwinian principles of variation, inheritance, differential reproduction and natural selection with Mendelian, experimental and population genetics, as well as with concepts and data addressing the patterns of evolution stemming from the fields of palaeontology, botany and systematics. It should not be used in discussion of the EES, which rarely makes any allusions to macroevolution, although it is sometimes forced to do so. Second, as is the case with most multilevel systems, developmental processes exhibit emergent properties. Only a brief overview of the most relevant conceptual innovations is possible in the present context. When natural selection affects such kinds of systems, the resulting phenotype variation does not need to be gradual and continuous. The science most central to the MS, genetics, likewise has substantially changed since the time of the synthesis and especially over the past two decades. In addition, novel genomic segments and biochemical functions can be acquired from other cells and organisms, rather than exclusively by inheritance from their progenitors. For instance, the theory largely avoids the question of how the complex organizations of organismal structure, physiology, development or behaviour—whose variation it describes—actually arise in evolution, and it also provides no adequate means for including factors that are not part of the population genetic framework, such as developmental, systems theoretical, ecological or cultural influences. These genuine predictions of the EES give rise to new research programmes, which have already generated validating empirical results. Adaptation as process: the future of Darwinism and the legacy of Theodosius Dobzhansky, How to rethink evolutionary theory: a plurality of evolutionary patterns, Does evolutionary theory need a rethink? Despite the fact that substantial challenges to these positions have arisen in the past decades from a host of different areas of biology, they have rarely resulted in alternative proposals. Rather than merely evoking the powers of computation for analysing multiple interactions of biological components, the capacity of systems biology is better interpreted as a scientific attitude that combines ‘reductionist’ approaches (study of constituent parts) with ‘integrationist’ approaches (study of internal and external interactions) [104]. (Online version in colour.). The defenders of the EES beg to differ: as long as the major predictions that can be derived from an evolutionary framework remain exactly those of the classical MS, no change to its core assumptions has happened. Naturwissenschaften 91, 255–276. In fact, our theoretical understanding of biological evolution has not remained unaltered. 2017 Oct 6;7(5):20160133. doi: 10.1098/rsfs.2016.0133. Adding a chapter or two on new domains of evolutionary research, as evolution textbooks increasingly do, does not mean that these concepts have been integrated into the theoretical edifice of evolutionary biology. Prominent evolutionary biologists and philosophers of science survey recent work that expands the core theoretical framework underlying the biological sciences. It has been over 60 years and evolution today includes mechanisms and even entire new fields that were not part of the foundational structure of the modern synthesis. The notion of slight successive variation was further reinforced by the molecular conception of genetic variation. Some of these results are in agreement with the standard theory and others reveal different properties of the evolutionary process. Proposals of an EES generally elicit rather positive reactions from the representatives of different fields of science, many of whom are convinced that an expanded theoretical framework has become necessary for evolutionary biology. The EES is not a simple, unfounded call for a new theory but has become an ongoing project for integrating the theoretically relevant concepts that have arisen from multiple fields of evolutionary biology. Below, I will sketch out an expanded framework to which several of the authors in this issue have contributed. Gould, and the extended synthesis, Punctuated equilibria: an alternative to phyletic gradualism, The so-called extended synthesis and population genetics, Philosophical Transactions of the Royal Society B: Biological Sciences, New trends in evolutionary biology: biological, philosophical and social science perspectives, http://creativecommons.org/licenses/by/4.0/, https://www.nature.com/news/does-evolutionary-theory-need-a-rethink-1.16080#/yes, https://www.nature.com/news/does-evolutionary-theory-need-a-rethink-1.16080#/noalliswell, doi:10.1002/1097-010X(20001215)288:4<304::AID-JEZ3>3.0.CO;2-G, Early in life effects and heredity: reconciling neo-Darwinism with neo-Lamarckism under the banner of the inclusive evolutionary synthesis. 8600 Rockville Pike In fact, simulations of the dynamical behaviours of gene regulatory networks in evolution demonstrate that bistable changes are more likely to occur than gradual transitions [64]. But in the past decade, without much notice by general audiences, a more wide-ranging debate has arisen from different areas of biology as well as from history and philosophy of science, about whether and in which ways evolutionary theory is affected, challenged or changed by the advances in biology and other fields.