Epigenetic inheritance and evolution: a historian's perspective.

The aim of this article is to put the growing interest in epigenetics in the field of evolutionary theory into a historical context. First, I assess the view that epigenetic inheritance could be seen as vindicating a revival of (neo)Lamarckism. Drawing on Jablonka's and Lamb's considerable output, I identify several differences between modern epigenetics and what Lamarckism was in the history of science. Even if Lamarckism is not back, epigenetic inheritance might be appealing for evolutionary biologists because it could potentiate two neglected mechanisms: the Baldwin effect and genetic assimilation. Second, I go back to the first ideas about the Baldwin effect developed in the late nineteenth century to show that the efficiency of this mechanism was already linked with a form of non-genetic inheritance. The opposition to all forms of non-genetic inheritance that prevailed at the time of the rise of the Modern Synthesis helps to explain why the Baldwin effect was understood as an insignificant mechanism during the second half of the twentieth century. Based on this historical reconstruction, in §4, I examine what modern epigenetics can bring to the picture and under what conditions epigenetic inheritance might be seen as strengthening the causal relationship between adaptability and adaptation. Throughout I support the view that the Baldwin effect and genetic assimilation, even if they are quite close, should not be conflated, and that drawing a line between these concepts is helpful in order to better understand where epigenetic inheritance might endorse a new causal role. This article is part of the theme issue 'How does epigenetics influence the course of evolution?'

Who's afraid of epigenetics? Habits, instincts, and Charles Darwin's evolutionary theory.

Our paper aims at bringing to the fore the crucial role that habits play in Charles Darwin's theory of evolution by means of natural selection. We have organized the paper in two steps: first, we analyse value and functions of the concept of habit in Darwin's early works, notably in his Notebooks, and compare these views to his mature understanding of the concept in the Origin of Species and later works; second, we discuss Darwin's ideas on habits in the light of today's theories of epigenetic inheritance, which describe the way in which the functioning and expression of genes is modified by the environment, and how these modifications are transmitted over generations. We argue that Darwin's lasting and multifaceted interest in the notion of habit, throughout his intellectual life, is both conceptually and methodologically relevant. From a conceptual point of view, intriguing similarities can be found between Darwin's (early) conception of habit and contemporary views on epigenetic inheritance. From a methodological point of view, we suggest that Darwin's plastic approach to habits, from his early writings up to the mature works, can provide today's evolutionary scientists with a viable methodological model to address the challenging task of extending and expanding evolutionary theory, with particular reference to the integration of epigenetic mechanisms into existing models of evolutionary change. Over his entire life Darwin has modified and reassessed his views on habits as many times as required by evidence: his work on this notion may represent the paradigm of a habit of good scientific research methodology.

Education, Experience, and Action: An Interview with Dr. Trevor K. Archer.

We asked Dr. Archer about his experiences in academia, struggles he has faced, and thoughts on addressing racial bias. We hope that this series sparks a larger discussion of issues faced by underrepresented scientists and ways the scientific community can foster diversity and better support underrepresented scientists. The opinions expressed here are those of Dr. Archer and not the NIH/NIEHS or the US government.

From 1957 to Nowadays: A Brief History of Epigenetics.

Due to the spectacular number of studies focusing on epigenetics in the last few decades, and particularly for the last few years, the availability of a chronology of epigenetics appears essential. Indeed, our review places epigenetic events and the identification of the main epigenetic writers, readers and erasers on a historic scale. This review helps to understand the increasing knowledge in molecular and cellular biology, the development of new biochemical techniques and advances in epigenetics and, more importantly, the roles played by epigenetics in many physiological and pathological situations.

Retrospective and perspective of plant epigenetics in China.

Epigenetics refers to the study of heritable changes in gene function that do not involve changes in the DNA sequence. Such effects on cellular and physiological phenotypic traits may result from external or environmental factors or be part of normal developmental program. In eukaryotes, DNA wraps on a histone octamer (two copies of H2A, H2B, H3 and H4) to form nucleosome, the fundamental unit of chromatin. The structure of chromatin is subjected to a dynamic regulation through multiple epigenetic mechanisms, including DNA methylation, histone posttranslational modifications (PTMs), chromatin remodeling and noncoding RNAs. As conserved regulatory mechanisms in gene expression, epigenetic mechanisms participate in almost all the important biological processes ranging from basal development to environmental response. Importantly, all of the major epigenetic mechanisms in mammalians also occur in plants. Plant studies have provided numerous important contributions to the epigenetic research. For example, gene imprinting, a mechanism of parental allele-specific gene expression, was firstly observed in maize; evidence of paramutation, an epigenetic phenomenon that one allele acts in a single locus to induce a heritable change in the other allele, was firstly reported in maize and tomato. Moreover, some unique epigenetic mechanisms have been evolved in plants. For example, the 24-nt siRNA-involved RNA-directed DNA methylation (RdDM) pathway is plant-specific because of the involvements of two plant-specific DNA-dependent RNA polymerases, Pol IV and Pol V. A thorough study of epigenetic mechanisms is of great significance to improve crop agronomic traits and environmental adaptability. In this review, we make a brief summary of important progress achieved in plant epigenetics field in China over the past several decades and give a brief outlook on future research prospects. We focus our review on DNA methylation and histone PTMs, the two most important aspects of epigenetic mechanisms.

Waddington's epigenetics or the pictorial meetings of development and genetics.

In 1956, in his Principles of Embryology, Conrad Hal Waddington explained that the word "epigenetics" should be used to translate and update Wilhelm Roux' German notion of "Entwicklungsmechanik" (1890) to qualify the studies focusing on the mechanisms of development. When Waddington mentioned it in 1956, the notion of epigenetics was not yet popular, as it would become from the 1980s. However, Waddington referred first to the notion in the late 1930s. While his late allusion clearly reveals that Waddington readily associated the notion of epigenetics with the developmental process, in the contemporary uses of the notion this developmental connotation seems to have disappeared. The advent and success of molecular biology have probably contributed to focusing biologists' attention on the "genetic" or the "non-genetic" over the "developmental". In the present paper, I first examine the links that exist, in Waddington's work, between the classical notion of epigenesis in embryology and those of epigenetics that Waddington proposed to connect, and even synthesize, data both from embryology and genetics. Second, I show that Waddington's own view of epigenetics has changed over time and I analyze how these changes appear through his many representations (both schematic or metaphorical images) of the relationships between genetic signals and developmental processes.

Epigenetics: the first 25 centuries.

Epigenetics is a natural progression of genetics as it aims to understand how genes and other heritable elements are regulated in eukaryotic organisms. The history of epigenetics is briefly reviewed, together with the key issues in the field today. This themed issue brings together a diverse collection of interdisciplinary reviews and research articles that showcase the tremendous recent advances in epigenetic chemical biology and translational research into epigenetic drug discovery.This article is part of a discussion meeting issue 'Frontiers in epigenetic chemical biology'.

Obituary: Denise Barlow (1950-2017).

Anne Ferguson-Smith and Marisa Bartolomei look back at the life and science of Denise Barlow, a pioneer in genomic imprinting and epigenetics.

Epigenetics: A way to bridge the gap between biological fields.

The concept of epigenetics has evolved since Waddington defined it from the late 1930s as the study of the causal mechanisms at work in development. It has become a multi-faceted notion with different meanings, depending on the disciplinary context it is used. In this article, we first analyse the transformations of the concept of epigenetics, from Waddington to contemporary accounts, in order to identify its different meanings and traditions, and to come up with a typology of epigenetics throughout its history. Second, we show on this basis that epigenetics has progressively turned its main focus from biological problems regarding development, toward issues concerning evolution. Yet, both these different epistemological aspects of epigenetics still coexist. Third, we claim that the classical opposition between epigenesis and preformationism as ways of thinking about the developmental process is part of the history of epigenetics and has contributed to its current various meanings. With these objectives in mind, we first show how Waddington introduced the term "epigenetics" in a biological context in order to solve a developmental problem, and we then build on this by presenting Nanney's, Riggs' and Holliday's definitions, which form the basis for the current conception of "molecular epigenetics". Then, we show that the evo-devo research field is where some particular uses of epigenetics have started shifting from developmental issues to evolutionary problems. We also show that epigenetics has progressively focused on the issue of epigenetic inheritance within the Extended Evolutionary Synthesis' framework. Finally, we conclude by presenting a typology of the different conceptions of epigenetics throughout time, and analyse the connections between them. We argue that, since Waddington, epigenetics, as an integrative research area, has been used to bridge the gap between different biological fields.

Russia's new Lysenkoism.

During the late 1940s and 1950s, a pseudo-scientific concept based on Marxist-Leninist ideology became internationally known as 'Lysenkoism'. Lysenkoism was a neo-Lamarckian idea, claiming that in crop plants, such as wheat, environmental influences are heritable via all cells of the organism. Lysenkoism was applied to agriculture during the Stalin era with disastrous consequences. Despite the triumphs of modern genetics, and the disproval of Lysenkoism, recent years have seen a 're-thinking' of this doctrine in Russia. This disturbing pro-Lysenko movement, which is accompanied by a growing sympathy for Stalin, claims to have its scientific roots in modern epigenetics, specifically the heritability of variation by mechanisms other than changes in DNA sequence. Based on recent research on the model plant Arabidopsis thaliana, its is clear that Lysenkoism has nothing to do with heritable 'epigenetic' modifications. Biologists should defend science against ideological and political interferences.

Fifty years of illumination about the natural levels of adaptation.

A visionary Darwinian ahead of his time, George C. Williams developed in his 1966 book Adaptation and Natural Selection the essentials of a unifying theory of adaptation that remains robust today and has inspired immense progress in understanding how natural selection works.

Epigenetics: ambiguities and implications.

Everyone has heard of 'epigenetics', but the term means different things to different researchers. Four important contemporary meanings are outlined in this paper. Epigenetics in its various senses has implications for development, heredity, and evolution, and also for medicine. Concerning development, it cements the vision of a reactive genome strongly coupled to its environment. Concerning heredity, both narrowly epigenetic and broader 'exogenetic' systems of inheritance play important roles in the construction of phenotypes. A thoroughly epigenetic model of development and evolution was Waddington's aim when he introduced the term 'epigenetics' in the 1940s, but it has taken the modern development of molecular epigenetics to realize this aim. In the final sections of the paper we briefly outline some further implications of epigenetics for medicine and for the nature/nurture debate.

Theorizing epigenesis in a time of preexistence: From the end of the seventeenth century to the 1720s.

According to a classic periodization in the history of science, biological thought as it emerged in France from the last decades of the seventeenth century to the 1740s was strongly committed to the doctrine of the preexistence of germs. Nicolas Malebranche's role in disseminating this paradigm, particularly in the milieu of the Académie Royale des Sciences during the years when Bernard Le Bouyer de Fontenelle was its secretary, has been studied in detail, especially by Jacques Roger. However, much less has been said about the authors who argued against this doctrine prior to the appearance of the relevant pieces by Pierre-Louis Moreau de Maupertuis, Georges-Louis Leclerc, Comte de Buffon, and Denis Diderot. I aim to examine a series of French medical treatises and clandestine manuscripts that outlined a mechanist theory of epigenesis, between the end of the seventeenth century and the 1720s, to bring to light the strategies-often quite original-that allowed them to achieve this result. One interesting case is the heterodox readers of Malebranche, which use some of his own arguments (notably on the physiology of brain traces and the laws of nature) both against preexistence and to support epigenesis. I inquire into the historical worth of the positions defended by these authors as well as into the connections existing between the history of epigenesis and that of materialism in the early modern era.

From Mendel to epigenetics: History of genetics.

The origins of genetics are to be found in Gregor Mendel's memoir on plant hybridization (1865). However, the word 'genetics' was only coined in 1906, to designate the new science of heredity. Founded upon the Mendelian method for analyzing the products of crosses, this science is distinguished by its explicit purpose of being a general 'science of heredity', and by the introduction of totally new biological concepts (in particular those of gene, genotype, and phenotype). In the 1910s, Mendelian genetics fused with the chromosomal theory of inheritance, giving rise to what is still called 'classical genetics'. Within this framework, the gene is simultaneously a unit of function and transmission, a unit of recombination, and of mutation. Until the early 1950s, these concepts of the gene coincided. But when DNA was found to be the material basis of inheritance, this congruence dissolved. Then began the venture of molecular biology, which has never stopped revealing the complexity of the way in which hereditary material functions.