R. Goldschmidt and J. Huxley: creative parallelisms

The comparative analysis of scientific heritage of Richard Goldschmidt and Julian Huxley shows convincingly the resemblance of these two scientists' views over the core problems of evolutionary theory, genetics and development biology. They both contributed to developing a triad "genetics--development--evolution". The problem of a relative growth of animals was the central point in both Goldschmidt's and Huxley's works. Huxley developed a formula of the allometric growth (law of constant differential growth) while Goldschmidt was the first to draw up the broad interpretation of the consequences of that phenomenon. Both scientists belonged to initiators of development genetics and used the "non-morganian" genetics in their efforts of solving problems of macroevolution. Goldschmidt tended toward an idea of an important role of macromutation in the process of macroevolution, though Huxley adhered to more moderate views. But at the same time the concept of preadaptive mutations proposed by Huxley was close to Goldschmidt's idea of macromutants. It is shown that both scientists analyzed profoundly the changes in early stages of embryogenesis in respect to macroevolution. It is not likely to be reasonable to oppose firmly Goldschmidt's saltationism to the evolutionary synthesis of Huxley. They developed the larger biological problems in a similar way, and undoubtedly their works in the field helped to enrich the development of the views over genetics and evolution. The open-minded analysis of Goldschmidt's and Huxley's concepts leads to creating modern and up-to-date views over the theory of evolution where seemingly incompatible things go together rather well and supplement each other. Evo-Devo rediscovered Goldshmidt's Biology and Huxley's Synthesis.     

Macromutations and Evolution: Fixation of Goldschmidt's Macromutations as Species and Genus Characters.* Papillomatosis and Appearance of Macrovilli in the Rodent Stomach

The cardiac portion of the stomach is lined with macrovilli in a few rodent genera. These are Mystromys (Cricetinae, Cricetidae), Myospalax (Myospalacinae, Cricetidae), Tachyoryctes (Tachyoryctinae, Cricetidae), and Cryptomys(Bathyergidae). The macrovilli favor the development of symbiotic flora and are called symbiovilli. Growth of the corneal epithelium of the cardiac portion of the stomach serves as a morphological basis of symbiovilli. Cases of a hereditary malignant neoplasm giving rise to the formation of multiple macrovilli in the cardiac portion of the stomach have been found in Microtus abbreviatus (Microtinae, Cricetidae), a vole endemic to St. Matthew Island in the Bering Sea. The macrovilli resulting from the papillomatosis mutation are morphologically and histologically identical to the macrovilli of the stomach of the four aforementioned genera. The voles affected with papillomatosis still survive long enough to reproduce. Therefore, the macromutation that leads to death in adult and old voles has been fixed as a species character in some rodent genera. At the early stages of papillomatosis, the pathogenic morphogenesis creates favorable conditions for the development of symbiotic microflora, which gives a selective advantage to the affected animals. It is assumed that mutations with pathogenic effects have been fixed as a species character as a result of heterochrony. The pathogenic neoplasm serves as a preadaptation for the growth of symbiotic flora in the stomach. The mechanisms of the fixation of Goldschmidt's systemic mutations during phylogeny are discussed.     

Macromutations and evolution: fixation of Goldschmidt's macromutations as species and genus characters. Papillomatosis and appearance of macrovilli in the rodent stomach

The cardiac portion of the stomach is lined with macrovilli in a few rodent genera. These are Mystromys (Cricetinae, Cricetidae), Myospalax (Myospalacinae, Cricetidae), Tachyoryctes (Tachyoryctinae, Cricetidae), and Cryptomys (Bathyergidae). The macrovilli favor the development of symbiotic flora and are called symbiovilli. Growth of the corneal epithelium of the cardiac portion of the stomach serves as a morphological basis of symbiovilli. Cases of a hereditary malignant neoplasm giving rise to the formation of multiple macrovilli in the cardiac portion of the stomach have been found in Microtus abbreviatus (Microtinae, Cricetidae), a vole endemic to St. Matthew Island in the Bering Sea. The macrovilli resulting from the papillomatosis mutation are morphologically and histologically identical to the macrovilli of the stomach of the four aforementioned genera. The voles affected with papillomatosis still survive long enough to reproduce. Therefore, the macromutation that leads to death in adult and old voles has been fixed as a species character in some rodent genera. At the early stages of papillomatosis, the pathogenic morphogenesis creates favorable conditions for the development of symbiotic microflora, which gives a selective advantage to the affected animals. It is assumed that mutations with pathogenic effects have been fixed as a species character as a result of heterochrony. The pathogenic neoplasm serves as a preadaptation for the growth of symbiotic flora in the stomach. The mechanisms of the fixation of Goldschmidt's "systemic mutations" during phylogeny are discussed.     

From Hopeful Monsters to Homeotic Effects: Richard Goldschmidt's Integration of Development, Evolution, and Genetics

Richard Goldschmidt's research on homeotic mutants from 1940until his death in 1958 represents one of the first seriousefforts to integrate genetics, development, and evolution. Usingtwo different models, Goldschmidt tried to show how differentviews of genetic structure and gene action could provide a mechanismfor rapid speciation. Developmental systems were emphasizedin one model and a hierarchy of genetic structures in the other.While Goldschmidt tried to find a balance between developmentand genetics, critics, such as Sewall Wright, urged him andeventually helped him incorporate population dynamics into hismodels as well. As such, the history of Goldschmidt's researchon homeotic mutants highlights the continuing challenge of producinga balanced and integrated developmental evolutionary genetics.     

On progressive evolution and competitive extinction

Synopsis Extinction may be caused by abiotic and biotic factors in the environment. In the present essay the focus is on extinction caused by biotic factors, and the problem is discussed with reference to two theories of evolution, micromutation and macromutation. According to the former, evolution is adaptive, implying that the only kind of extinction is pseudoextinction or gradual extinction, reflecting the mechanism through which evolution advances in small steps. The macromutation theory asserts that two kinds of evolution exist, divergent (adaptive) and progressive. The latter steadily gives rise to more dominant forms in the phylogenetic hierarchy, and whenever these have a chance to compete with inferior organisms, they will cause the extermination of the latter. However, primitive forms may survive in isolation. The predictions of the macromutation theory are shown to be in better agreement with the fossil record and other observations than are those of the micromutation theory.Invited Editorial     

TESTING MACROEVOLUTIONARY HYPOTHESES WITH CLADISTIC ANALYSIS: EVIDENCE AGAINST RECTANGULAR EVOLUTION

The properties of cladistic data sets from small monophyletic groups (6–12 species) are investigated using computer simulations of macroevolution. Two evolutionary models are simulated: gradualism and the punctuated-equilibrium hypothesis. Under the conditions of our simulations these two models of evolution make consistently different predictions about the distribution of autapomorphies among species. When strict stasis is enforced, the punctuated-equilibrium hypothesis predicts that the most expected number of autapomorphies per species will be zero, no matter how many characters are used in the analysis. As the number of characters used in the analysis increases, the distribution of the number of autapomorphies per species becomes bimodal. Under gradualism, the distribution of autapomorphies remains unimodal under all conditions, but the number of species without autapomorphies can fall to zero. A survey of real cladograms of extant monophyletic groups from a wide range of taxa indicates that the predictions of the punctuated-equilibrium hypothesis about autapomorphies do not hold. This constitutes strong evidence against the punctuated-equilibrium hypothesis.     

Ancon sheep: a now disproven example of macroevolution.

The Ancon breed of sheep provided, for decades, a critical support for the existence of major evolutionary changes or jumps called "sports." Putative examples of sports have been used as evidence of rapid macroevolution since Darwin first discussed the Ancon sheep mutation in 1859. Ancon sheep had very short legs that were considered an advantage for shepherds because the sheep were less likely to escape over fences. Many textbooks and articles implied that the breed was an example of how a major new trait could evolve in a single generation. The Ancon sheep example has been used both to prove gradual Darwinism and also to argue for rapid evolution as opposed to gradualism. It now is recognized that Ancon sheep resulted from genetic diseases, and that they usually suffered from achondroplasia. The so-called new breed had so many major health problems that the condition caused the breed's extinction decades ago, yet was mentioned in textbooks as evidence for evolutionary jumps as recently as 2005.     

“And then a miracle occurs” — weak links in the chain of argument from punctuation to hierarchy

Weak links, in the form of inadequacies in both reasoning and supporting evidence, exist at several critical steps in the derivation of an hierarchical concept of evolution from punctuated equilibria. Punctuation itself is predicated on a distorted reading of phyletic change as phyletic gradualism, and of allopatric speciation as the instantaneous formation of unchanging typological taxa. The concept of punctuation is further confounded by the indescriminate employment of the same term to denote both a causal explanation for evolutionary change and an outcome of substantiated evolutionary processes. Even when the intended usage for the term is specified, each denotation of punctuation entails respective drawbacks. As a causal explanation, punctuation clearly belongs to the class of quantum theories with all their attendant impedimenta, including special salsatory non-adaptive mechanisms of evolutionary change. Redefinition of punctuation as a pattern of morphologic change reduces it to one possible outcome of known microevolutioanry processes, thus obviating any need for an hierarchical explanation of macroevolution. While vacillation between usages has preserved the term in the literature, the end result of this obfuscation has been a circle of faulty reasoning in which the pattern of punctuation is invoked as its own proof. Widespread confusion concerning what constitutes an adequate test of punctuation is directly attributable to imprecision in both the original and revised formulations of the concept.The argument for species-level selection is based on the typological and philosphically flawed premise of species as individuals, and further requires the hypothesis of heritable emergent properties, for which empirical evidence is lacking.Extrapolation of hierarchy to higher taxonomic levels depends on the unproven assumption that mass extinction constitutes a causal mechanism for macroevolution which is qualitatively distinct from, and not reducible to, the causes of microevolution.Because key elements of hierarchical theory depend upon misrepresentations of the synthetic theory, semantic circumvention, and questionable reasoning, and because its central assertions remain unsubstantiated by empirical evidence, the derivation of an hierarchical theory of evolution from punctuation constitutes an exercise an futility and should be abandoned.     

The proper place of hopeful monsters in evolutionary biology

Hopeful monsters are organisms with a profound mutant phenotype that have the potential to establish a new evolutionary lineage. The Synthetic Theory of evolutionary biology has rejected the evolutionary relevance of hopeful monsters, but could not fully explain the mechanism and mode of macroevolution. On the other hand, several lines of evidence suggest that hopeful monsters played an important role during the origin of key innovations and novel body plans by saltational rather than gradual evolution. Homeotic mutants are identified as an especially promising class of hopeful monsters. Examples for animal and plant lineages that may have originated as hopeful monsters are given. Nevertheless, a brief review of the history of the concept of hopeful monsters reveals that it needs refinements and empirical tests if it is to be a useful addition to evolutionary biology. While evolutionary biology is traditionally zoocentric, hopeful monsters might be more relevant for plant than for animal evolution. Even though during recent years developmental genetics has provided detailed knowledge about how hopeful monsters can originate in the first place, we know almost nothing about their performance in natural populations and thus the ultimate difference between hopeful and hopeless. Studying the fitness of candidate hopeful monsters (suitable mutants with profound phenotype) in natural habitats thus remains a considerable challenge for the future.     

Zum konzept der »inneren« selektion: Stellungnahme zu einer evolutionstheoretischen kontroverse

Recently the concept of natural selection in Darwin’s sense has been criticized by some authors. It has been argued that this concept does not explain certain phenomena of evolutionary change, especially in the reach of macroevolution. Some biologists, therefore, demanded for evolution a new model of selection which focuses internal factors in phytogeny. — This paper is a brief discussion of some aspects of “internal” selection and its meaning in contemporary evolutionary biology. The argument of the paper is that evolution can only be explained by a theory taking cognizance of interactions between external and internal selective agencies. Such a theory would be a systems theory of evolution.     

Symbiogenesis,natural selection,and the dynamic Earth

One century ago, Constantin S. Mereschkowsky introduced the symbiogenesis theory for the origin of chloroplasts from ancient cyanobacteria which was later supplemented by Ivan E. Wallin’s proposal that mitochondria evolved from once free-living bacteria. Today, this Mereschkowsky–Wallin principle of symbiogenesis, which is also known as the serial primary endosymbiosis theory, explains the evolutionary origin of eukaryotic cells and hence the emergence of all eukaryotes (protists, fungi, animals and plants). In 1858, the concept of natural selection was described independently by Charles Darwin and Alfred R. Wallace. In the same year, Antonio Snider-Pellegrini proposed the idea of shifting continents, which was later expanded by Alfred Wegener, who published his theory of continental drift eight decades ago. Today, directional selection is accepted as the major cause of adaptive evolution within natural populations of micro- and macro-organisms and the theory of the dynamic Earth (plate tectonics) is well supported. In this article, I combine the processes and principles of symbiogenesis, natural selection and the dynamic Earth and propose an integrative ‘synade-model’ of macroevolution which takes into account organisms from all five Kingdoms of life.     

The concept of macroevolution in view of modern data

Macroevolution, or evolution of superspecies taxa is the process of transformation of “organismal” life flows on the Earth during its geological history. In the present study, this process is analyzed with using the system and evolutionarily?ecological approaches. Based on modern paleontological, evolutionary biological, molecular, and genetic data, mostly on vertebrates and hominins, the major factors and patterns of macroevolution and also the role of macroevolution in the biosphere evolution are discussed. The fundamental bases of the concept of macroevolution, the problems of methodology and methods of the study of organismal evolution are considered. It is shown that the processes at the macroevolutionary level agree with the epigenetic theory of evolution.     

Approaches to Macroevolution: 1. General Concepts and Origin of Variation

Approaches to macroevolution require integration of its two fundamental components, i.e. the origin and the sorting of variation, in a hierarchical framework. Macroevolution occurs in multiple currencies that are only loosely correlated, notably taxonomic diversity, morphological disparity, and functional variety. The origin of variation within this conceptual framework is increasingly understood in developmental terms, with the semi-hierarchical structure of gene regulatory networks (GRNs, used here in a broad sense incorporating not just the genetic circuitry per se but the factors controlling the timing and location of gene expression and repression), the non-linear relation between magnitude of genetic change and the phenotypic results, the evolutionary potential of co-opting existing GRNs, and developmental responsiveness to nongenetic signals (i.e. epigenetics and plasticity), all requiring modification of standard microevolutionary models, and rendering difficult any simple definition of evolutionary novelty. The developmental factors underlying macroevolution create anisotropic probabilities—i.e., an uneven density distribution—of evolutionary change around any given phenotypic starting point, and the potential for coordinated changes among traits that can accommodate change via epigenetic mechanisms. From this standpoint, “punctuated equilibrium” and “phyletic gradualism” simply represent two cells in a matrix of evolutionary models of phenotypic change, and the origin of trends and evolutionary novelty are not simply functions of ecological opportunity. Over long timescales, contingency becomes especially important, and can be viewed in terms of macroevolutionary lags (the temporal separation between the origin of a trait or clade and subsequent diversification); such lags can arise by several mechanisms: as geological or phylogenetic artifacts, or when diversifications require synergistic interactions among traits, or between traits and external events. The temporal and spatial patterns of the origins of evolutionary novelties are a challenge to macroevolutionary theory; individual events can be described retrospectively, but a general model relating development, genetics, and ecology is needed. An accompanying paper (Jablonski in Evol Biol 2017) reviews diversity dynamics and the sorting of variation, with some general conclusions.     

Towards an alternative evolution model

Lamarck and Darwin agreed on the inconstancy of species and on the exclusive gradualism of evolution (nature does not jump). Darwinism, revived as neo-Darwinism, was almost generally accepted from about 1930 till 1960. In the sixties the evolutionary importance of selection has been called in question by the neutralists. The traditional conception of the gene is disarranged by recent molecular-biological findings. Owing to the increasing confusion about the concept of genotype, this concept is reconsidered. The idea of the genotype as a cluster of genes is replaced by a cybernetical interpretation of the genotype. As nature does jump, exclusive gradualism is dismissed. Saltatory evolution is a natural phenomenon, provoked by a sudden collapse of the thresholds which resist against evolution. The fossil record and the taxonomic system call for a macromutational interpretation. As Lamarck and Darwin overlooked the resistance of evolutionary thresholds, an alternative evolution model is needed, the first to be constructed on a palaeontological and taxonomic basis.Progress emerges from error, far more than from chaos. (Gray, 1963)     

Homoeotic and atavic mutations in insects

A comparative analysis of the known types of homoeotic mutantsin insects uncovers the existence of invariants in the homoeotictransformations. Mutations change individual segments and individualcompartments into one another leaving other developmental coordinatesunchanged. Clonal analysis of some favorable mutants shows thatthe homoeotically transformed organ or region (allotype) andthe organ or region it mimics (telotype) are developmentallyidentical. From this it is concluded that the function of thewildtype allele is to repress the developmental characteristicof the telotype in the affected organ or region (autotype).Since homoeotic mutations are specific to compartments and doublemutants show an additive effect, it is concluded that theirwildtype genes act in a combinatorial way, defining a givendevelopmental pathway. The establishment and maintenance ofa given step in this pathway may be affected by mutations indifferent loci. Genetic and developmental analyses of thesemutations suggest that they are related in a sequence of regulatorysteps. The consideration of these findings leads to an operationalmodel for explaining genetic control of developmental pathwaysduring ontogenesis and evolution.     

Neoteny, evolution and the New Zealand Parsonsia hybrids (Apocynaceae)

The striking diversification of leaf shape in juveniles of the hybrids between Parsonsia heterophylla A. Cunn. and P. capsularis (Forst. f.) R. Br. is described and illustrated. The applicability of Turing's diffusion reaction theory of morphogenesis was tested, and it was found that the diversity could be explained as a result of interactions between sine-wave-like gradients of morphogens in the leaf primordia. Precession in the onset of sexual maturity leads to the fixation of juvenile leaf characters. This neotenic process combined with natural selection may then lead to speciation and adaptive radiation, as in the Australian Parsonsia spp. The operation of these processes in other New Zealand genera and in Australian Proteaceae is discussed in relation to adaptive radiation and evolution.     

Explanations in evolutionary theory1

The theory of biological evolution is defined in many ways, leading to considerable confusion in its application and testing against objective empirical observations. Evolutionary change is usually defined as genetic which would exclude both cultural and template evolution; hence the qualifying adjective genetic should not be included in the definition of biological evolution. Darwin's theory, always described by him in the singular, is actually a bundle of five independent theories about evolution as advocated by Mayr. Furthermore only one of these theories, that of common descent, is historical, and the other four – evolution as such, gradualism, processes of phyletic evolution and of speciation, and causes of evolution – are nomological. Hence not all evolutionary theory is historical. Biological comparisons can be divided into horizontal and vertical ones and valid conclusions from one type of comparisons cannot be automatically extrapolated to the other. All phyletic evolutionary change, no matter how extensive it may be, never crosses species taxa boundaries; hence it is not possible to distinguish ‘trans‐specific evolution’ (= evolution beyond or above the level of the species) from evolution within the species level. Macroevolution does not differ from microevolution except in the scale of the overall change; no special causes or processes of macroevolution exist.     

Examining the Interaction of Acceptance and Understanding: How Does the Relationship Change with a Focus on Macroevolution?

The goal of this research was to illuminate the relationship between students’ acceptance and understanding of macroevolution. Our research questions were: (1) Is there a relationship between knowledge of macroevolution and acceptance of the theory of evolution?; (2) Is there a relationship between the amount of college level biology course work and acceptance of evolutionary theory and knowledge of macroevolution?; and (3) Can college student acceptance of the theory of evolution and knowledge of macroevolution change over the course of a semester? The research participants included 667 students from a first-semester biology course and 74 students from the evolutionary biology course. Data were collected using both the MATE (a measure of the acceptance of evolutionary theory) and the MUM (a measure of understanding of macroevolution). Pre-instruction data were obtained for the introductory biology course, and pre- and post-data were obtained for the evolutionary biology course. Analysis revealed acceptance of evolution (as measured by the MATE) was correlated to understanding of macroevolution, and the number of biology courses was significantly correlated to acceptance and knowledge of macroevolution. Finally, there was a statistically significant change in students’ understanding of macroevolution and acceptance of evolution after the one-semester evolutionary biology course. Significance of these findings is discussed.     

Early 20th-century research at the interfaces of genetics, development, and evolution: reflections on progress and dead ends

Three early 20th-century attempts at unifying separate areas of biology, in particular development, genetics, physiology, and evolution, are compared in regard to their success and fruitfulness for further research: Jacques Loeb's reductionist project of unifying approaches by physico-chemical explanations; Richard Goldschmidt's anti-reductionist attempts to unify by integration; and Sewall Wright's combination of reductionist research and vision of hierarchical genetic systems. Loeb's program, demanding that all aspects of biology, including evolution, be studied by the methods of the experimental sciences, proved highly successful and indispensible for higher level investigations, even though evolutionary change and properties of biological systems up to now cannot be fully explained on the molecular level alone. Goldschmidt has been appraised as pioneer of physiological and developmental genetics and of a new evolutionary synthesis which transcended neo-Darwinism. However, this study concludes that his anti-reductionist attempts to integrate genetics, development and evolution have to be regarded as failures or dead ends. His grand speculations were based on the one hand on concepts and experimental systems that were too vague in order to stimulate further research, and on the other on experiments which in their core parts turned out not to be reproducible. In contrast, Sewall Wright, apart from being one of the architects of the neo-Darwinian synthesis of the 1930s, opened up new paths of testable quantitative developmental genetic investigations. He placed his research within a framework of logical reasoning, which resulted in the farsighted speculation that examinations of biological systems should be related to the regulation of hierarchical genetic subsystems, possibly providing a mechanism for development and evolution. I argue that his suggestion of basing the study of systems on clearly defined properties of the components has proved superior to Goldschmidt's approach of studying systems as a whole, and that attempts to integrate different fields at a too early stage may prove futile or worse.     

Genetic Analysis of the Antennapedia Gene Complex (Ant-C) and Adjacent Chromosomal Regions of DROSOPHILA MELANOGASTER. II. Polytene Chromosome Segments 84A-84B1,2

The existence of a gene complex in the proximal right arm of chromosome 3 of Drosophila melanogaster involved in the development of the head and thorax was originally suggested by the phenotypes of several dominant homoeotic mutations and their revertants. A screen for mutations utilizing Df(3R) Antp^Ns+R17 (proximally broken in salivary region 84B1,2) yielded, among 102 recovered mutations, 17 localized by deficiency mapping to the putative homoeotic cluster. These fell into four complementation groups, two of which were characterized by homoeotic phenotypes. To explore the limits of the Antennapedia gene complex (ANT-C) more proximally, a second screen has been undertaken utilizing Df(3R)Scr, a deficiency of 84A1–B1,2.—Of 2832 chromosomes screened, 21 bearing alterations localized to polytene interval 84A–84B1,2 have been recovered. Sixteen are recessive lethals, and five showing reduced viability display a visible phenotype in surviving individuals. Complementation and phenotypic analyses revealed four complementation groups proximal to those identified in the previous screen, including two new alleles of the recessive homoeotic mutation, proboscipedia (pb). Ten of the new mutations correspond to complementation groups defined previously in the Df(3R)Antp^Ns+R17 screen four to the EbR11 group, two to the Scr group and four to the Antp group.—On the basis of the phenotypes of the 39 mutations localized to this region, plus their interactions with extant homoeotic mutations, we postulate that there are at least five functional sites comprising the ANT-C. Three have been demonstrated to be homoeotic in nature. The specific homoeotic transformations thus far observed suggest that these loci are critical for normal development of adult labial, maxillary and thoracic structures.