Waddington’s Processual Epigenetics and the Debate over Cryptic Variability

2018 ◽  
Author(s):  
Flavia Fabris
Keyword(s):  
Genetic Variation ◽  
Evolutionary Biology ◽  
Modern Synthesis ◽  
Genetic Assimilation ◽  
Ontological Difference ◽  
Epigenetic Process ◽  
Recent Debate ◽  
Acquired Characters

This chapter reappraises Waddington’s processual theory of epigenetics and examines its implications for contemporary evolutionary biology. It focuses in particular on the ontological difference between two conflicting assumptions that have been conflated in the recent debate over the nature of cryptic variability: a substance view that is consistent with the modern synthesis and construes variability as a preexisting pool of random genetic variation; and a processual view, which derives from Waddington’s conception of developmental canalization and understands variability as an epigenetic process. The chapter also discusses how these opposing interpretations fare in their capacity to explain the genetic assimilation of acquired characters.

Challenging the Modern Synthesis

2017 ◽  
Keyword(s):  
21St Century ◽  
Evolutionary Biology ◽  
Modern Synthesis ◽  
Early 20Th Century ◽  
Theory Of Evolution ◽  
Original Essays ◽  
New Biology ◽  
Conceptual Foundations ◽  
Orthodox View

Since its origin in the early 20th century, the modern synthesis theory of evolution has grown to represent the orthodox view on the process of organic evolution. It is a powerful and successful theory. Its defining features include the prominence it accords to genes in the explanation of development and inheritance, and the role of natural selection as the cause of adaptation. Since the advent of the 21st century, however, the modern synthesis has been subject to repeated and sustained challenges. In the last two decades, evolutionary biology has witnessed unprecedented growth in the understanding of those processes that underwrite the development of organisms and the inheritance of characters. The empirical advances usher in challenges to the conceptual foundations of evolutionary theory. Many current commentators charge that the new biology of the 21st century calls for a revision, extension, or wholesale rejection of the modern synthesis theory of evolution. Defenders of the modern synthesis maintain that the theory can accommodate the exciting new advances in biology, without forfeiting its central precepts. The original essays collected in this volume—by evolutionary biologists, philosophers of science, and historians of biology—survey and assess the various challenges to the modern synthesis arising from the new biology of the 21st century. Taken together, the essays cover a spectrum of views, from those that contend that the modern synthesis can rise to the challenges of the new biology, with little or no revision required, to those that call for the abandonment of the modern synthesis.

scholarly journals Sex, amitosis, and evolvability in the ciliate Tetrahymena thermophila

2021 ◽  
Author(s):  
Jason A Tarkington ◽  
Hao Zhang ◽  
Ricardo Azevedo ◽  
Rebecca Zufall
Keyword(s):  
Genetic Variation ◽  
Experimental Evolution ◽  
Evolutionary Biology ◽  
Genetic Architecture ◽  
Nuclear Division ◽  
Tetrahymena Thermophila ◽  
Laboratory Populations ◽  
Evolutionary Success ◽  
Sexual Progeny ◽  
Open Question

Understanding the mechanisms that generate genetic variation, and thus contribute to the process of adaptation, is a major goal of evolutionary biology. Mutation and genetic exchange have been well studied as mechanisms to generate genetic variation. However, there are additional processes that may also generate substantial genetic variation in some populations and the extent to which these variation generating mechanisms are themselves shaped by natural selection is still an open question. Tetrahymena thermophila is a ciliate with an unusual mechanism of nuclear division, called amitosis, which can generate genetic variation among the asexual descendants of a newly produced sexual progeny. We hypothesize that amitosis thus increases the evolvability of newly produced sexual progeny relative to species that undergo mitosis. To test this hypothesis, we used experimental evolution and simulations to compare the rate of adaptation in T. thermophila populations founded by a single sexual progeny to parental populations that had not had sex in many generations. The populations founded by a sexual progeny adapted more quickly than parental populations in both laboratory populations and simulated populations. This suggests that the additional genetic variation generated by amitosis of a heterozygote can increase the rate of adaptation following sex and may help explain the evolutionary success of the unusual genetic architecture of Tetrahymena and ciliates more generally.

Development and evolution

1997 ◽  
Author(s):  
John Maynard Smith ◽  
Eors Szathmary
Keyword(s):  
Evolutionary Biology ◽  
Recent Progress ◽  
Sound Production ◽  
Germ Line ◽  
Black Box ◽  
Developmental Genetics ◽  
Morphological Form ◽  
Molecular Information ◽  
Acquired Characters ◽  
Development And Evolution

In the nineteenth century, ideas about development, heredity and evolution were inextricably mixed up, because it seemed natural to suppose that changes that first occurred in development could become hereditary, and so could contribute to evolution. This was not only Lamarck’s view but Darwin’s, expressed in his theory of pangenesis. Weismann liberated us from this confusion, by arguing that information could pass from germ line to soma, but not from soma to germ line. If he was right, geneticists and evolutionary biologists could treat development as a black box: transmission genetics and evolution could be understood without first having to understand development. Since Weismann, developmental biology has had only a rather marginal impact on evolutionary biology. One day, we have promised ourselves, we will open the box, but for the time being we can get along very nicely without doing so. Recent progress in developmental genetics, some of which has been reviewed in the last three chapters, oblige us to reopen the question. In fact, there are three related questions, not one. The first, which is most relevant to the theme of this book, is the ‘levels of selection’ question: why does not selection between the cells of an organism disrupt integration at the level of the organism? This is the topic of section 15.2. The second is the problem of the inheritance of acquired characters. This old problem has reappeared in a new guise. We now recognize the existence of cell heredity, mediated by different mechanisms from those concerned with transmitting information between generations. In section 15.3, we discuss whether cell heredity plays any role in evolutionary change. Finally, in sections 15.4 and 15.5, we ask whether recent molecular information sheds any light on another old problem—that of the extraordinary conservatism of morphological form, maintained despite dramatic changes of function. This conservatism has led anatomists to identify a small number of basic archetypes, or bauplans. There is little doubt that conservatism is real. Consider, for example, the fact that bones and cartilages, which in humans serve in swallowing, sound production and hearing, are derived from elements of the gill apparatus whereby our fish ancestors exchanged gases with seawater, and, before that, in all probability, from elements of a filter-feeding apparatus.

Oligogenic Adaptation, Soft Sweeps, and Parallel Melanic Evolution in Drosophila melanogaster

2016 ◽  
Author(s):  
Héloïse Bastide ◽  
Jeremy D. Lange ◽  
Justin B. Lack ◽  
Yassin Amir ◽  
John E. Pool
Keyword(s):  
Drosophila Melanogaster ◽  
Genetic Variation ◽  
Evolutionary Biology ◽  
Genetic Architecture ◽  
Genetic Basis ◽  
Simulation Analysis ◽  
Mapping Method ◽  
Sub Saharan Africa ◽  
Mountain Ranges ◽  
Sub Saharan

AbstractUnraveling the genetic architecture of adaptive phenotypic divergence is a fundamental quest in evolutionary biology. In Drosophila melanogaster, high-altitude melanism has evolved in separate mountain ranges in sub-Saharan Africa, potentially as an adaptation to UV intensity. We investigated the genetic basis of this melanism in three populations using a new bulk segregant analysis mapping method. Although hundreds of genes are known to affect cuticular pigmentation in D. melanogaster, we identified only 19 distinct QTLs from 9 mapping crosses, with several QTL peaks being shared among two or all populations. Surprisingly, we did not find wide signals of genetic differentiation (Fst) between lightly and darkly pigmented populations at these QTLs, in spite of the pronounced phenotypic difference in pigmentation. Instead, we found small numbers of highly differentiated SNPs at the probable causative genes. A simulation analysis showed that these patterns of polymorphism are consistent with selection on standing genetic variation (leading to “soft sweeps“). Our results thus support a role for oligogenic selection on standing genetic variation in driving parallel ecological adaptation.

Sympatric Speciation in the Post “Modern Synthesis” Era of Evolutionary Biology

2012 ◽  
Vol 39 (2) ◽  
pp. 158-180 ◽  
Author(s):  
Christopher E. Bird ◽  
Iria Fernandez-Silva ◽  
Derek J. Skillings ◽  
Robert J. Toonen
Keyword(s):  
Evolutionary Biology ◽  
Sympatric Speciation ◽  
Modern Synthesis

scholarly journals Loss of genetic variation in the two-locus multiallelic haploid model

2020 ◽  
Author(s):  
Martin Pontz ◽  
Marcus W. Feldman
Keyword(s):  
Game Theory ◽  
Genetic Variation ◽  
Global Attractor ◽  
Evolutionary Biology ◽  
Selection Models ◽  
Fitness Parameters ◽  
Unequal Number ◽  
Haploid Selection ◽  
Additional Assumptions

AbstractIn the evolutionary biology literature, it is generally assumed that in deterministic haploid selection models, in the absence of variation-generating mechanisms such as mutation, no polymorphic equilibrium can be stable. However, results corroborating this claim are scarce and almost always depend upon additional assumptions. Using ideas from game theory, we establish a condition on the fitness parameters of haplotypes formed by two loci such that a monomorphism is a global attractor. Further, we show that no isolated equilibrium exists, at which an unequal number of alleles from two loci is present. Under the assumption of convergence of trajectories to equilirium points, we settle the two-locus three-allele case for a fitness scheme formally equivalent to the classical symmetric viability model.

scholarly journals What Future for Evolutionary Biology? Response to Commentaries on “The Illusions of the Modern Synthesis”

Biosemiotics ◽  
2021 ◽  
Author(s):  
Denis Noble
Keyword(s):  
Evolutionary Biology ◽  
Modern Synthesis ◽  
The Other ◽  
Target Article ◽  
Wide Range ◽  
Extensive Range ◽  
The Way

Abstract The extensive range and depth of the twenty commentaries on my target article (Noble, 2021) confirms that something has gone deeply wrong in biology. A wide range of biologists has more than met my invitation for “others to pitch in and develop or counter my arguments.” The commentaries greatly develop those arguments. Also remarkably, none raise issues I would seriously disagree with. I will focus first on the more critical comments, summarise the other comments, and then point the way forward on what I view as a necessary and long-overdue transition in the foundations of biology.

Genetic Assimilation and the Paradox of Blind Variation

2017 ◽  
Author(s):  
Arnaud Pocheville ◽  
Étienne Danchin
Keyword(s):  
Genetic Variation ◽  
Natural Selection ◽  
Genetic Assimilation ◽  
Random Mutation ◽  
Empirical Claim ◽  
Hypothetical Mechanism

This chapter confronts the neo-Darwinian core tenet of blind variation, or random mutation, with classical and recent models of genetic assimilation. We first argue that all the mechanisms proposed so far rely on blind genetic variation fueling natural selection. Then, we examine a new hypothetical mechanism of genetic assimilation, relying on nonblind genetic variation. Yet, we show that such a model still relies on blind variation of some sort to explain adaptation. Last, we discuss the very meaning of the tenet of blind variation. We propose a formal characterization of the tenet and argue that it should not be understood solely as an empirical claim, but also as a core explanatory principle.

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