ABSTRACT
Resumo Em 1868, Darwin publica seu livro The variation of animals and plants under domestication, no qual expõe sua teoria da hereditariedade. Nela se encontrava o pressuposto de que o desenvolvimento era fundamental para compreensão do processo evolutivo. No presente trabalho, é feita uma releitura da teoria darwiniana da pangênese, no intuito de rediscutir seu valor histórico. Conclui-se que a teoria da pangênese estava bem adequada a seu tempo e, mais do que isso, é possível encontrar ressonâncias de seu pressuposto em trabalhos das novas áreas biologia evolutiva do desenvolvimento (evo-devo) e epigenética.
Abstract In 1868, Darwin published his book The variation of animals and plants under domestication, which laid out his theory of heredity. This included the assumption that development was essential to understanding the evolutionary process. This present article reassesses the Darwinian theory of pangenesis in order to revisit its historical value. The conclusion is that the theory of pangenesis was well-suited to its time, and additionally, reflections of this assumption can be found in work in new areas known as evolutionary biology of development (evo-devo) and epigenetics.
Subject(s)
Humans , Biology , EpigenomicsABSTRACT
The standard model of evolutionary change of form, deriving from Darwin’s theory via the Modern Synthesis, assumes a gradualistic reshaping of anatomical structures, with major changes only occurring by many cycles of natural selection for marginal adaptive advantage. This model, with its assertion that a single mechanism underlies both micro- and macroevolutionary change, contains an implicit notion of development which is only applicable in some cases. Here we compare the embryological processes that shape the vertebrate limb bud, the mammalian tooth and the avian beak. The implied notion of development in the standard evolutionary picture is met only in the case of the vertebrate limb, a single-primordium organ with morphostatic shaping, in which cells rearrange in response to signalling centres which are essentially unchanged by cell movement. In the case of the tooth, a single-primordium organ with morphodynamic shaping in which the strengths and relationships between signalling centres is influenced by the cell and tissue movements they induce, and the beak, in which the final form is influenced by the collision and rearrangement of multiple tissue primordia, abrupt appearance of qualitatively different forms (i.e. morphological novelties) can occur with small changes in system parameters induced by a genetic change, or by an environmental factor whose effects can be subsequently canalized genetically. Bringing developmental mechanisms and, specifically, the material properties of tissues as excitable media into the evolutionary picture, demonstrates that gradualistic change for incremental adaptive advantage is only one of the possible modes of morphological evolution.
ABSTRACT
A controversy of relevance to the study of biological form involves the concept of adaptation. This controversy is illustrated by the structure and function of the human hand. A review of the principal definitions of adaptation points to two main problems: (1) they are qualitative and make reference to the whole structure (or substructural feature) and (2) they are based on the idea of natural selection as a moulding factor. The first problem would be solved by a definition that encompasses quantitative measures of the effects of selection, drawing on new advances in the comparative method. The second problem is deeper and presents greater conceptual difficulties. I will argue that the idea of natural selection as a moulding factor depends on the notion of a genetic program for development. But regarding the hand, experimental evidence on limb development challenges the idea of a genetic program for skeletal pattern formation, undermining a simple application of standard adaptationist concepts. These considerations lead to a revised definition of adaptation and interpretation of the evolutionary determinants of the hand’s form.
ABSTRACT
Noggin, along with other secreted bone morphogenetic protein (BMP) inhibitors, plays a crucial role in neural induction and neural tube patterning as well as in somitogenesis, cardiac morphogenesis and formation of the skeleton in vertebrates. The BMP signalling pathway is one of the seven fundamental pathways that drive embryonic development and pattern formation in animals. Understanding its evolutionary origin and role in pattern formation is, therefore, important to evolutionary developmental biology (evo-devo).We have studied the evolutionary origin of BMP–Noggin antagonism in hydra, which is a powerful diploblastic model to study evolution of pattern-forming mechanisms because of the unusual cellular dynamics during its pattern formation and its remarkable ability to regenerate. We cloned and characterized the noggin gene from hydra and found it to exhibit considerable similarity with its orthologues at the amino acid level. Microinjection of hydra Noggin mRNA led to duplication of the dorsoventral axis in Xenopus embryos, demonstrating its functional conservation across the taxa. Our data, along with those of others, indicate that the evolutionarily conserved antagonism between BMP and its inhibitors predates bilateral divergence. This article reviews the various roles of Noggin in different organisms and some of our recent work on hydra Noggin in the context of evolution of developmental signalling pathways.
ABSTRACT
Aunque no lo suficientemente conocida y difundida, la obra botánica de Darwin aportó una gran cantidad de evidencia empírica fundamental para el establecimiento de la revolución darwinista. Se describe el desarrollo de esta obra, en especial con relación a los dos mentores de Darwin en botánica: J. S. Henslow y J. D. Hooker. Además de numerosos artículos y notas en sus diarios de viaje, su correspondencia y numerosos apartes de sus dos obras magnas El origen de las especies y selección natural, Darwin escribió siete libros relacionados con diversos aspectos de la botánica, incluída la polinización en orquídeas, la morfología y fisiología de plantas trepadoras, la domesticación, las plantas insectívoras, la polinización, las formas florales, y los movimientos de las plantas. Cada uno de estos libros es ahora clásico en cada tema. La introducción de la teoría evolutiva en la sistemática de plantas enriqueció los distintos sistemas de clasificación en los 70 años que siguieron a la publiación de El origen, lo cual está en estrecha relación con las preguntas, aún vigentes, acerca del origen y la diversificación temprana de las angiospermas. A la vez, se revisa la influencia de las contribuciones botánicas de Darwin en las obras de autores en diversos países de Europa y América, y en disciplinas tan diversas y actuales como la biogeografía, la biología reproductiva en muy diversos grupos de plantas con flor, la citología y mecanismos de herencia en la célula vegetal, la teratología vegetal, las variaciones debidas a domesticación, y la reciente integración de evolución, genética y desarrollo en la disciplina conocida como evo-devo.
Despite Darwin s botanical works are not sufficiently known, they provided a large amount of critical, empirical evidence in favor of the darwinian revolution. This paper describes the development of such works in connection to the influence of two of Darwin s mentors in botany, J. S. Henslow and J. D. Hooker. Besides numerous articles, field notes, extensive correspondence, and Darwin s main books, The Origin of Species and Natural Selection, he wrote seven books related to different botanical issues, including orchid pollination, morphology and physiology of climbers, domestication, insectivorous plants, cross-and self-pollination, floral forms, and plant movements. Each of these volumes became classic on each topic. The introduction of the evolutionary theory in plant systematics had a positive effect by increasing the systems of classification during the 70 years following the publication of The Origin, which is in close relation to the still unresolved questions about the origin and early diversification of angiosperms. In addition, we review the influence of Darwin s contributions in European and American authors, as well as in current disciplines such as biogeography, reproductive biology, citology and mechanisms of heredity in the plant cell, plant teratology, plant domestication, and the new integration of evolution, genetics and development under the discipline known as evo-devo.