From unicellularity to multicellularity - molecular speculations about early animal evolution

A morphological, physiological, developmental, and genetic organization of great complexity ineluctably unfolded from relatively simple phenomena invested with enormous potential. Sometime long ago in the Protererozoic times, parasitic invasions caused lower evolutionary levels to integrate into higher-level selection. Therefore, we have a multi-level selection problem that ultimately revolves around the question of how natural selection among lower-level units acts to create higher-level units of selection, in which Darwinian competition among replicators ceases to be the foremost force. The first level relinquishes its independence for the benefit of a higher-level cooperative force that is now the criterion of fitness for the new transition in the evolutionary process.

From geochemistry and biochemistry to prebiotic evolution... we necessarily enter into Gánti's fluid automata

The present study is just an overview of the opening of the geochemical stage for the appearance of life. But that opening would not have been sufficient for the intellectual discovery of the origin of life! The excellent works and many commendable efforts that advance this explanation have not shown the fundamental elements that participate in the theoretical frame of biological evolution. The latter imply the existence of evolutionary transitions and the production of new levels of organization. In this brief analysis we do not intend to introduce the audience to the philosophy of biology. But we do expect to provide a modest overview, in which the geochemical chemolithoautotrophic opening of the stage should be seen, at most, as the initial metabolism that enabled organic compounds to follow the road where a chemical fluid machinery was thus able to undertake the more [quot ]sublime[quot ] course of organic biological evolution. We think that Tibor Gánti's chemoton is the most significant contribution to theoretical biology, and the only course now available to comprehend the unit of evolution problem without the structuralist and functionalist conflict prevalent in theoretical biology. In our opinion Gánti's chemoton theory travels to the [quot ]locus[quot ] where evolutionary theory dares to extend itself to entities at many levels of structural organization, beyond the gene or the group above. Therefore, in this and subsequent papers on the prebiotic conditions for the eventual appearance of the genetic code, we explore the formation and the presence of metal sulfide minerals, from the assembly of metal sulfide clusters through the precipitation of nanocrystals and the further reactions resulting in bulk metal sulfide phases. We endeavor to characterize pristine reactions and the modern surfaces, utilizing traditional surface science techniques and computational methods. Moreover, mechanistic details of the overall...

Evolution without speciation but with selection: LUCA, the Last Universal Common Ancestor in Gilbert's RNA world

This is not an attempt to analyze the Last Universal Common Ancestor (LUCA) to understand the origin of living systems. We do not know what came before Gilberts' RNA world. Our analysis starts with the RNA world and with genes (biological replicators alla Dawkings) made up of RNA proteins with enzymatic catalytic functions within units that are not yet modern cells. We offer a scenario where cellular entities are very simple and without individuality; they are only simple primary units of selection (the first level of selection) in which replicators compete in the most Darwinian manner, totally deprived of cooperation and interactions among genes. The information processing system of this RNA world is inaccurate and inefficient when compared to that found in organisms that came later. Among the [quot ]genes[quot ] and the entities that harbor them, high mutation rate was the most prevalent source of variability and the only inheritance was through lateral gene transfer of mobile elements. There were no chromosomes or any other genomic organization. As millions of years accumulated, complex and organized biological structures and processes evolved thanks to the variability mustered up mostly by lateral gene transfers and mutations. With micro- and mini-satellites, lateral gene transfers became indispensable devices of selection to mold variability. Competition and Darwinian selection gave way to a new transition in evolution, one I consider ineluctable, in which cooperation among interactive genes prevailed for the sake of higher fitness. Compartmentalization constituted a major transition in evolution that spurted new types of genome organization. Minichromosomes is one of these; cellular membranes and cytoplasmic structures completed the picture of the primitive cell. However, the much talked about phylogenetic tree does not exit in that ancient LUCA. The tree has no organism at its base; only clusters of genes evoke a fragile beginning for the increasingly complex cell types that were to emerge later

Non-Darwinian and Darwinian prokaryotic and eukaryotic evolution--an enigma in cell biology conservation

Our theory is embarrassingly simple. What made today's prokaryotes and modern cyanobacteria so robust is the fact that in their origin, back in the Archean (3 billion years ago), selection did not play a central role in evolution, it had only a transitory role. Asexual reproduction, mutation, drift and sampling variance in local demes were more important especially when they were accompanied by population catastrophes, where millions perished. Metazoans are generally macroscopic, sexually reproducing, ecologically specialized organisms whose history is full of extinctions and radiations leading to morphological change. On the other hand, prokaryotes, thanks to their origin, avoid extinction because as a group they have slowly evolved as generalists. Specialization appears to be less important than ecological versatility and metabolic unspecialization. Modern cyanobacteria keep on using that strategy

Cell biology, molecular embryology, Lamarckian and Darwinian selection as evolvability

The evolvability of vertebrate systems involves various mechanisms that eventually generate cooperative and nonlethal functional variation on which Darwinian selection can operate. It is a truism that to get vertebrate animals to develop a coherent machine they first had to inherit the right multicellular ontogeny. The ontogeny of a metazoan involves cell lineages that progressively deny their own capacity for increase and for totipotency in benefit of the collective interest of the individual. To achieve such cell altruism Darwinian dynamics rescinded its original unicellular mandate to reproduce. The distinction between heritability at the level of the cell lineage and at the level of the individual is crucial. However, its implications have seldom been explored in depth. While all out reproduction is the Darwinian measure of success among unicellular organisms, a high replication rate of cell lineages within the organism may be deleterious to the individual as a functional unit. If a harmoniously functioning unit is to evolve, mechanisms must have evolved whereby variants that increase their own replication rate by failing to accept their own somatic duties are controlled. For questions involving organelle origins, see Godelle and Reboud, 1995 and Hoekstra, 1990. In other words, modifiers of conflict that control cell lineages with conflicting genes and new mutant replication rates that deviate from their somatic duties had to evolve. Our thesis is that selection at the level of the (multicellular) individual must have opposed selection at the level of the cell lineage. The metazoan embryo is not immune to this conflict especially with the evolution of set-aside cells and other modes of self-policing modifiers (Blackstone and Ellison, 1998; Ransick et al., 1996. In fact, the conflict between the two selection processes permitted a Lamarckian soma-to-germline feedback loop. This new element in metazoan ontogeny became the evolvability of the vertebrate adaptive immune system and life as we know it now. We offer the hypothesis that metazoan evolution solved this ancient conflict by evolving an immunogenetic mechanism that responds with rapid Lamarckian efficiency by retaining the ancient reverse transcriptase enzyme (RNACopyright DNA copying discovered by Temin in 1959 (see Temin, 1989) and found in 1970 in RNA tumor viruses by Temin and Baltimore), which can produce cDNA from the genome of an RNA virus that infects the cells. It seems that molecular

Conflicting genomes, the demic theory & biodiversity

O darwinismo centrado nos organismos, para usar fenótipos diretos para medir os efeitos da seleçäo natural, requer harmonia e coerência uniforme do genoma, além de populaçöes de grande tamanho. Contudo, o darwinismo moderno, centrado no gene, tem encontrado novas interpretaçöes para dados que falam de incoerência e desarmonia genômica. Como resultado dessas duas posiçöes conflitantes, uma crise conceitual nasceu na Biologia. Minha posiçäo é que a presença de demes de diminuto tamanho, é importante para gerar divergências e crise fenotípica; além disso, a presença de genomas parasitas, como em vermes acantocéfalos, que chegam a manipular comportamentos suicidas em seus hospedeiros; distorcedores de segregaçäo que alteram a meiose e as taxas mendelianas; genes egoístas e cromossomas inteiros egoístas, tais como no caso de cromossomos B do gafanhoto; elementos P da Drosophila; cromossomos Y que manipulam as taxas sexuais, fazendo com que os machos sejam mais freqüentes, como no "drive" ligado ao X de Hamilton; e genes estratégia macho e fora-da-lei säo exemplos eloqüentes da presença de genomas conflitantes reais e de uma coerência fenotípica e harmonia genômica näo uniformes. Assim, nós propomos que a incoerência e a desarmonia em geral geram desordem, mas também geram mais biodiversidade e criatividade. Finalmente, se os genes podem manipular a seleçäo natural, eles podem multiplicar as mutaçöes ou as características indesejáveis e mesmo as letais ou deletérias, daí o acúmulo de cargas genéticas. Genes fora-da-lei podem mudar o que é conveniente adaptativamente, mesmo no sentido do carácter que se afasta do ótimo. O ótimo pode ser "negociado" entre as variantes näo apenas porque os efeitos pleiotrópicos assim o exigem, mas também, em alguns casos, porque genes egoístas ou fora-da-lei ou elementos P ou manipulaçäo fenótipica externa assim o requerem. Com o darwinismo organísmico, o genoma na populaçäo e no indivíduo era considerado como agindo harmoniosamente sem conflitos e os genótipos caminhavam em direçäo a uma maior adaptabilidade. O darwinismo moderno tem uma visäo centrada no gene, em que os genes, como objetos da seleçäo natural, podem mudar em dissonância no sentido que beneficia sua multiplicaçäo. Assim, existem maiores oportunidades para os genomas que estäo em permanente conflito.

La crisis poblacional / Population crisis

Con una visión Genética se analiza el vertiginoso crecimiento poblacional que presenta la especie humana y las repercusiones en su fertilidad y en las demás instancias fisiológicas, sico-sociales, de comportamiento del espacio físico, con sus consecuencias culturales y ambientales. Plantea la necesidad de que cada uno de los paises del mundo ejecuten políticas poblacionales con el fin de incrementar un control natal que logre una tasa de crecimiento cero, para optimizar las características genéticas fisiológicas, nutricionales, evolutivas y de recursos del hombre