Biogenesis

Dehydration/condensation reactions between organic molecules in the prebiotic environment increased the inventory and complexity of organic compounds available for self-assembly into primitive cellular organisms. As a model of such reactions and to demonstrate this principle, we have investigated the esterification reaction between glycerol and decanoic acid that forms glycerol monodecanoate (GMD). This amphiphile enhances robustness of self-assembled membranous structures of carboxylic acids to the potentially disruptive effects of pH, divalent cation binding and osmotic stress. Experimental variables included temperature, water activity and hydrolysis of the resulting ester product, providing insights into the environmental conditions that would favor the formation and stability of this more evolved amphiphile. At temperatures exceeding 50 degrees C, the ester product formed even in the presence of bulk water, suggesting that the reaction occurs at the liquid interface of the two reactants and that the products segregate in the two immiscible layers, thereby reducing hydrolytic back reactions. This implies that esterification reactions were likely to be common in the prebiotic environment as reactants underwent cycles of wetting and drying on rare early landmasses at elevated temperatures.

There is no broadly accepted definition of 'life.' Suggested definitions face problems, often in the form of robust counter-examples. Here we use insights from philosophical investigations into language to argue that defining 'life' currently poses a dilemma analogous to that faced by those hoping to define 'water' before the existence of molecular theory. In the absence of an analogous theory of the nature of living systems, interminable controversy over the definition of life is inescapable.

It is commonly accepted among origin-of-life scientists that the emergence of life was an evolutionary process involving at one stage or other the working of natural selection. Researchers disagree, however, on the nature of the chemical infrastructure that could have formed prebiotically, enabling the evolutionary process. The division of the origin-of-life research community into ‘geneticists’ and ‘metabolists’ usually revolves around the issue whether the first to arise prebiotically was a genetic polymer or a primitive metabolic system. In this paper I offer an alternative classification based on the attitude to the onset of natural selection. From this perspective I add to the conventional division between gene-first and metabolism-first groups a position I call “preparatory metabolism”. By this line of thought, an RNA or an RNA-like polymer could not have emerged prebiotically. Nevertheless, the onset of natural selection had to wait until such a polymer had arised. This paper examines the RNA-first, RNA-later, metabolism-first and preparatory-metabolism scenarios, assessing the weaknesses and strengths of each. I conclude that despite the recent theoretical advances in all these lines of research, and despite experimental breakthroughs, especially in overcoming several RNA-first hurdles, none of the examined paradigms has yet attained decisive experimental support. Demonstrating the evolvability of a potentially prebiotic infrastructure, whether genetic or metabolic, is a most serious challenge. So is the experimental demonstration of the emergence of such an infrastructure under prebiotic conditions. The current agenda before origin-of-life researchers of all stripes and colors is the search for the experimental means to tackle all these difficulties.

The discovery of hydrothermal vents at oceanic ridge crests and the appreciation of their importance in the element balance of the oceans is one of the main recent advances in marine geochemistry 1 . It is likely that vents were present in the oceans of the primitive Earth because the ...

Antropología Filosófico-teológica tiene como objeto reflexionar sobre el ser humano y tiene cuatro campos que se corresponden con las intencionalidades que son: 

- Mostrar los orígenes y la realidad universo como el campo donde el ser humano estira y ahonda su raíz. El universo, y en él la tierra, que es anterior a todo viviente, constituye la patria y casa en la que la vida es. (Primera parte).

- Exponer las visiones de ser humano que van desde las filosofías orientales (Confucianismo, Hinduismo y Budismo), pasando brevemente por las visiones que se tienen en la filosofía griega (Sócrates, Platón y Aristóteles), en la filosofía patrística (Agustín de Hipona y Tomás de Aquino), en la filosofía moderna (Descartes y Kant), en la filosofía cristiana, hasta la visión del mismo en la en las historias y cosmovisiones en el Continente América. (Segunda parte).

- Explicitar al ser humano como un ser integral y pluridimensional que se hace en la historia y en el tiempo concretos. (Tercera parte).

- Presentar al Hombre Jesús de Nazareth quien a partir de su praxis y su proyecto liberador que tienen como objeto la construcción de un mundo justo y como destinatarios a los excluidos, se constituye en la revelación y panificación de la historia del ser humano en la historia del mundo y en la historia de Dios. (Cuarta parte).

Consciente de que ni el universo ni el ser humano están concluidos, este trabajo que trata de realidades inconclusas tampoco queda concluido, está abierto a toda crítica y aporte interdisciplinario.

Vicente Plasencia LLanos

Sumario 1. Raíces etimológicas y concepto de antropología 2. El lugar de la antropología en el concierto de las ciencias 3. Horizontes de la ciencia antropología 4. Teorías que explican el origen del universo y del ser humano 5. El recorrido de la pregunta del ser humano por el ser humano 6. Cuestiones antropológicas polémicas 7. Una aclaración al ¿por qué de una antropología personalista y cristiana? Introducción La antropología es una ciencia que nace con el ser humano pero que se ha sistematizado en los siglos XVII y XVIII y, sin embargo, sigue siendo una ciencia inacabada. Dicha ciencia tiene muchas acentuaciones y todas ellas convergen en las preguntas y respuestas que el ser humano se plantea para sí mismo tratando de comprender su identidad. En este horizonte, la pregunta que ha sido y es conductora de estas plurales y diferentes investigaciones es: ¿qué es el hombre?. Sin embargo, para responder a la cuestión del ser humano por el ser humano, son necesarios unos marcos conceptuales comunes que nos permitan contextualizar el fenómeno en cuestión, por eso, en este apartado trataré de presentar unas nociones generales de la ciencia objeto de estudio. Así entonces, empezaré por las raíces etimológicas y el esbozo de un posible concepto de la antropología; seguidamente pasaré a ver una contextualización científica de la ciencia antropología en el cosmos de las demás ciencias; continuaré con las teorías que explican el origen del ser humano; abordaré el recorrido de la pregunta conductora del tema macro y, con ella abriré la puerta hacia una antropología biológica, cultural y religiosa. Puesto que he sostenido que abriré la puerta hacia una antropología religiosa, quiero precisar que no estoy refiriéndome de ninguna manera a una visión necesariamente cristiana sino a esa actitud de apertura por parte de todo ser humano hacia la Trascendencia, experiencia humana que permitirá re-conocer algunos elementos que más tarde orientarán hacia la comprensión de una antropología que quiere ser de corte cristiana. (Ver Parte IV de este texto)

All known cosmic and geological conditions and laws of chemistry and thermodynamics allow that complex organic matter could have formed spontaneously on pristine planet Earth about 4,000 mya. Simple gasses and minerals on the surface and in oceans of the early Earth reacted and were eventually organized in supramolecular aggregates and enveloped cells that evolved into primitive forms of life. Chemical evolution, which preceded all species of extant organisms, is a fact. In this review, we have concentrated on experimental and theoretical research published over the last two decades, which has added a wealth of new details and helped to close gaps in our previous understanding of this multifaceted field. Recent exciting progress in the molecular and genetic analyses of existing life, in particular microorganisms of ancient origin, even supports the possibility that a cellular, self-reproducing common ancestor might be assembled and resurrected in anaerobic cultures at some time in the future. Charles Darwin did not, and indeed, could not, address and specify the earliest phases of life which preceded the Origin of Species. However, in a famous letter, he sketched “a warm little pond with all sorts of… (chemicals, in which) …a protein was chemically formed.” We try to trace the impact of his charming clear-sighted metaphor up to the present time.

¿Qué es el hombre? es la pregunta en la que el ser humano se revela a sí mismo como un problema y, el intento de aproximarse a una respuesta “conduce a mantenerse en alerta en su proceso, históricamente contextualizado, de humanización”. En este texto el autor realiza un acercamiento al problema del ser humano desde una perspectiva filosófica y teológica, mostrándolo como parte del entramado del proceso de la evolución cósmica que, habiendo llegado hasta la consciencia y la libertad en la cima de la evolución, se humaniza de modo contextualizado y plural; este ser humano, en su complejidad constitutiva, es uno y pluridimensional y, su realización historizada se da en el despliegue de sus dimensiones corporeo-sexuada, mundano-historizada, racio-intelectiva, psico-afectiva, intersubjetiva/social, de libertad, ético-política y trascendente y; cuanto ser espiritual y trascendente, esto es perspectiva cristiana, encuentra su derrotero en la historia de Jesús de Nazareth quien desde la historia concreta traza el camino de emancipación y liberación desde las víctimas. El texto responde radicalmente a los diálogos inter-pluri-trans-disciplinares ejercidos en las cátedras del Área Razón y Fe de la Universidad Politécnica Salesiana-Ecuador. El autor deja abierto el desafío de reflexión sobre el “Ser humano: Un pro-yecto inconcluso”. (Tomado del original de la contratapa del texto)

Spectacular advances in structural and molecular biology have added support to the 'RNA world' hypothesis, and provide a mandate for chemistry to explain how RNA might have been generated prebiotically on the early earth. Difficulties in achieving a prebiotically plausible synthesis of RNA, however, have led many to ponder the question posed in the title of this paper. Herein, we review recent experimental work on the assembly of potential RNA precursors, focusing on methods for stereoselective C-C bond construction by aldolisation and related processes. This chemistry is presented in the context of a broader picture of the potential constitutional self-assembly of RNA. Finally, the relative accessibility of RNA and alternative nucleic acids is considered.

Understanding the origin of cellular life on Earth requires the discovery of plausible pathways for the transition from complex prebiotic chemistry to simple biology, defined as the emergence of chemical assemblies capable of Darwinian evolution. We have proposed that a simple primitive cell, or protocell, would consist of two key components: a protocell membrane that defines a spatially localized compartment, and an informational polymer that allows for the replication and inheritance of functional information. Recent studies of vesicles composed of fatty-acid membranes have shed considerable light on pathways for protocell growth and division, as well as means by which protocells could take up nutrients from their environment. Additional work with genetic polymers has provided insight into the potential for chemical genome replication and compatibility with membrane encapsulation. The integration of a dynamic fatty-acid compartment with robust, generalized genetic polymer replication would yield a laboratory model of a protocell with the potential for classical Darwinian biological evolution, and may help to evaluate potential pathways for the emergence of life on the early Earth. Here we discuss efforts to devise such an integrated protocell model.

The first systems of molecules having the properties of the living state presumably self-assembled from a mixture of organic compounds available on the prebiotic Earth. To carry out the polymer synthesis characteristic of all forms of life, such systems would require one or more sources of energy to activate monomers to be incorporated into polymers. Possible sources of energy for this process include heat, light energy, chemical energy, and ionic potentials across membranes. These energy sources are explored here, with a particular focus on mechanisms by which self-assembled molecular aggregates could capture the energy and use it to form chemical bonds in polymers. Based on available evidence, a reasonable conjecture is that membranous vesicles were present on the prebiotic Earth and that systems of replicating and catalytic macromolecules could become encapsulated in the vesicles. In the laboratory, this can be modeled by encapsulated polymerases prepared as liposomes. By an appr...

[Pre-print of a paper published in Progress of Biophysics and Molecular Biology, September 2012]

]The fundamental problem posed by Darwin distinguishes his theory from any transformism of the past as well as any evolutionism to come: since variation is inherent to the living, it is a question of explaining, not at all why the living varies, but instead why the living does not vary in all directions to the point of constituting a continuum of forms varying ad infinitum. What limits and stabilizes this intrinsically unlimited variation, allowing certain forms to subsist and multiply to the detriment of others, is natural selection. This double principle of intrinsic variation/extrinsic selection constitutes a vector for the unification of reality that underlies Jean-Jacques Kupiec's ontophylogenesis as well as Deleuze and Guattari's global philosophy of Nature. Therefore, everything would potentially tend to incessantly vary. The work of Kupiec and others identifies an intrinsic random variation within ontogenesis itself. For Deleuze and Guattari, it is nothing but the figure, already selected by the organic stratum, of a more fundamental or pure variation. But, in fact, nothing really varies incessantly: everything undergoes a selective pressure according to which nothing subsists as such except what manages to endure through invariance (physical stratum) or reproduction (organic stratum). Thus, organic stratification only retains from variation what ensures and augments this reproduction. In this sense, every organism stratifies, i.e. submits to its imperative of subsistence and reproduction, a body without organs that varies in itself and always tends to escape the organism, for better (intensifications of life) or worse (cancerous pathologies).

Stable, hydrogen-burning, M dwarf stars comprise about 75% of all stars in the Galaxy. They are extremely long-lived and because they are much smaller in mass than the Sun (between 0.5 and 0.08 MSun), their temperature and stellar luminosity are low and peaked in the red. We have re-examined what is known at present about the potential for a terrestrial planet forming within, or migrating into, the classic liquid-surface-water habitable zone close to an M dwarf star. Observations of protoplanetary disks suggest that planet-building materials are common around M dwarfs, but N-body simulations differ in their estimations of the likelihood of potentially-habitable, wet planets residing within their habitable zones, which are only ~ 1/5 to 1/50 of the width of that for a G star. Particularly in light of the claimed detection of the planets with masses as small as 5.5 and 7.5 MEarth orbiting M stars, there seems no reason to exclude the possibility of terrestrial planets. Tidally locked synchronous rotation within the narrow habitable zone doesn't necessarily lead to atmospheric collapse, and active stellar flaring may not be as much of an evolutionarily disadvantageous factor as has previously been supposed. We conclude that M dwarf stars may indeed be viable hosts for planets on which the origin and evolution of life can occur. A number of planetary processes such as cessation of geothermal activity, or thermal and non-thermal atmospheric loss processes may limit the duration of planetary habitability to periods far shorter than the extreme lifetime of the M dwarf star. Nevertheless, it makes sense to include M dwarf stars in programs that seek to find habitable worlds and evidence of life.

During the Hadean to early Archean period (4.5-3.5 Ga), the surface of the Earth's crust was predominantly composed of basalt and komatiite lavas. The conditions imposed by the chemical composition of these rocks favoured the crystallization of Fe-Mg clays rather than that of Al-rich ones (montmorillonite). Fe-Mg clays were formed inside chemical microsystems through sea weathering or hydrothermal alteration, and for the most part, through post-magmatic processes. Indeed, at the end of the cooling stage, Fe-Mg clays precipitated directly from the residual liquid which concentrated in the voids remaining in the crystal framework of the mafic-ultramafic lavas. Nontronite-celadonite and chlorite-saponite covered all the solid surfaces (crystals, glass) and are associated with tiny pyroxene and apatite crystals forming the so-called "mesostasis". The mesostasis was scattered in the lava body as micro-settings tens of micrometres wide. Thus, every square metre of basalt or komatiite rocks was punctuated by myriads of clay-rich patches, each of them potentially behaving as a single chemical reactor which could concentrate the organics diluted in the ocean water. Considering the high catalytic potentiality of clays, and particularly those of the Fe-rich ones (electron exchangers), it is probable that large parts of the surface of the young Earth participated in the synthesis of prebiotic molecules during the Hadean to early Archean period through innumerable clay-rich micro-settings in the massive parts and the altered surfaces of komatiite and basaltic lavas. This leads us to suggest that Fe,Mg-clays should be preferred to Al-rich ones (montmorillonite) to conduct experiments for the synthesis and the polymerisation of prebiotic molecules.

The continuity of abiotically formed bilayer membranes with similar structures in contemporary cellular life, and the requirement for microenvironments in which large and small molecules could be compartmentalized, support the idea that amphiphilic boundary structures contributed to the emergence of life. As an extension of this notion, we propose here a `Lipid World' scenario as an early evolutionary step in