Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Origin of Life”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 757 records · Page 42Linked to original sources
PubMed2006

Pereskia and the origin of the cactus life-form.

The cactus life-form is cited as an example of a tight relationship between organism form and function: a succulent, long-lived, photosynthetic stem allows cacti to survive long periods of drought while maintaining a positive tissue water status. Pereskia (Cactaceae) comprises 17 species of leafy shrubs and trees that are thought to represent the original cactus condition. Recent phylogenetic work has shown that there are two separate clades of Pereskia species, which are basal and paraphyletic with respect to the rest of the cacti. We selected seven Pereskia species, representing both clades, and characterized their water relations by measuring a suite of physiological traits in wild populations. Additionally, we estimated basic climate parameters from collection localities for all 17 Pereskia species. Extant Pereskia species exhibit ecological water use patterns that are very similar to those of the leafless, stem-succulent cacti. Ancestral trait reconstruction for the physiological and environmental data provides a preliminary assessment of the ecology and water relations of the earliest cacti and suggests that several key elements of the cactus ecological niche were established before the evolution of the cactus life-form. We interpret these ecological traits as potentially important drivers of evolutionary innovation in the cacti.

Biological Evolution↗
PubMed2004

[Cribra orbitalia, dentin hypoplasia and life expectancy of 20-year-old persons as social and sex specific stress indicators in correlation with the health status of an early medieval population].

The aim of this study is based on the analysis of diachronically social and sexual specific considerations on the life situation of the early medieval population of Schleitheim, Kanton Schaffhausen, Switzerland. Cribra orbitalia and the linear enamel hypoplasia of the teeth are considered as stressors. This study is based on the life expectancy of the 20 years old, as the life expectancy gives information on the health condition of a social group or an entire population. The considered indicators show the same tendencies in three of the four social groups (women social group A and group B/C, men of the social group A). The female and male population of the social group A show a steady decrease in the indicator from the 5th century to come to its lowest level in the 7th century. The same parameters indicate a continuous increase in stress for the female population of the group B/C. Only one of the three indicators, the Cribra orbitalia, shows a positive tendency in the male population of the social group B/C from the 6th century to the following period, while hypoplasia and the life expectancy on the other hand indicate a negative tendency. The results show equal tendencies in the three independent indicators concerning three of the four social groups. This proves the high reliability of the indicators. These results are astonishing in two ways. First of all, the tendencies show that the originally better life situation of women of the higher ranking social group decreases in the following periods, whereas the women of the lower social group show an inverse development. This female population of low life situation in the 5th century shows an increase in life qualities in the following periods. Remarkable, too, is the fact, that the female population of both social groups shows a lower level of stress than the corresponding male population. This fact is astonishing, as we would expect inverse results in a patriarchal society. This may point to a well known fact: Women show a higher vitality than the male population.

Adult↗
PubMed2004

Basic autonomy as a fundamental step in the synthesis of life.

In the search for the primary roots of autonomy (a pivotal concept in Varela's comprehensive understanding of living beings), the theory of autopoiesis provided an explicit criterion to define minimal life in universal terms, and was taken as a guideline in the research program for the artificial synthesis of biological systems. Acknowledging the invaluable contribution of the autopoietic school to present biological thinking, we offer an alternative way of conceiving the most basic forms of autonomy. We give a bottom-up account of the origins of "self-production" (or self-construction, as we propose to call it), pointing out which are the minimal material and energetic requirements for the constitution of basic autonomous systems. This account is, indeed, committed to the project of developing a general theory of biology, but well grounded in the universal laws of physics and chemistry. We consider that the autopoietic theory was formulated in highly abstract terms and, in order to advance in the implementation of minimal autonomous systems (and, at the same time, make major progress in exploring the origins of life), a more specific characterization of minimal autonomous systems is required. Such a characterization will not be drawn from a review of the autopoietic criteria and terminology (à la Fleischaker) but demands a whole reformulation of the question: a proper naturalization of the concept of autonomy. Finally, we also discuss why basic autonomy, according to our account, is necessary but not sufficient for life, in contrast with Varela's idea that autopoiesis was a necessary and sufficient condition for it.

Artificial Intelligence↗
PubMed1996

End of life decisions at the beginning of life.

Modern neonatal intensive care technology enhances the ability to maintain vulnerable newborns. In some circumstances survival may be insufficient justification for care. "End of life" strategies, originally applicable to adults, are being considered for newborns. Unresolved ethical issues in the care of these newborns involve multiple considerations. Concern occurs regarding patient-centered beneficence, non-maleficence, distributive justice, futility, legal rights of infants, and autonomy. The benefits to a newborn of treatment may fail to overcome the burdens of subsequent life. Under what circumstances a newborn loses the right to have life prolonged becomes a difficult ethical issue. With time and debate the proper response will become implemented.

Decision Making↗
PubMed2002

Mechanisms influencing bone metabolism in chronic illness.

Bone is permanently renewed by the coordinated actions of bone-resorbing osteoclasts and bone-forming osteoblasts, which model and remodel bone structure during growth and adult life. The origin of osteoblastic cells (osteoblasts, osteocytes and bone-lining cells) differs from that of osteoclasts, but both cell groups communicate with each other using cytokines and cell-cell contact as to optimally maintain bone homeostasis. This communication in many ways uses the same players as the communication between cells in the immune system. During acute life-threatening illness massive bone resorption is the rule, while bone formation is suppressed. During chronic illness, the balance between bone formation and bone resorption also shifts, frequently resulting in decreased bone mass and density. Several factors may contribute to the osteopenia that accompanies chronic illness, the most important being undernutrition and low body weight, inflammatory cytokines, disorders of the neuroendocrine axis (growth hormone/IGF-1 disturbances, thyroid and gonadal deficiency), immobilization, and the long-term use of glucocorticoids. Their combined effects not only influence the generation and activity of all bone cells involved, but probably also regulate their life span by apoptotic mechanisms. Osteopenia or even osteoporosis and bone fragility, and before puberty also decreased linear growth and lower peak bone mass are therefore frequent consequences of chronic illnesses.

Adult↗
PubMed2002

Thermodynamics of biological evolution and aging. Supramolecular thermodynamics is a key to understanding phenomena of life. What is life from a physical chemist's viewpoint.

The law of temporal hierarchies of the biological world allows us to pick out of the biomass quasi-closed thermodynamic systems with a given hierarchy. It has been established, that the use of this law of Nature as applied to supramolecular structures of organisms allows us the opportunity of using the methods of equilibrium supramolecular thermodynamics in the examination of open living systems. It has been shown that supramolecular thermodynamics is one of the "keys", which allows us to explain the origin of life and evolution of living beings. The second law of thermodynamics in its classic formulation (R. Clausius, J.W. Gibbs) is easy to apply in order to make calculations, carried out through methods of chemical, supramolecular and overall hierarchical thermodynamics.

Aging↗
PubMed1993

Evolution of the glutamine synthetase gene, one of the oldest existing and functioning genes.

We performed molecular phylogenetic analyses of glutamine synthetase (GS) genes in order to investigate their evolutionary history. The analyses were done on 30 DNA sequences of the GS gene which included both prokaryotes and eukaryotes. Two types of GS genes are known at present: the GSI gene found so far only in prokaryotes and the GSII gene found in both prokaryotes and eukaryotes. Our study has shown that the two types of GS gene were produced by a gene duplication which preceded, perhaps by > 1000 million years, the divergence of eukaryotes and prokaryotes. The results are consistent with the facts that (i) GS is a key enzyme of nitrogen metabolism found in all extant life forms and (ii) the oldest biological fossils date back 3800 million years. Thus, we suggest that GS genes are one of the oldest existing and functioning genes in the history of gene evolution and that GSI genes should also exist in eukaryotes. Furthermore, our study may stimulate investigation on the evolution of "preprokaryotes," by which we mean the organisms that existed during the era between the origin of life and the divergence of prokaryotes and eukaryotes.

Animals↗
PubMed1996

Models of parasite virulence.

Several evolutionary processes influence virulence, the amount of damage a parasite causes to its host. For example, parasites are favored to exploit their hosts prudently to prolong infection and avoid killing the host. Parasites also need to use some host resources to reproduce and transmit infections to new hosts. Thus parasites face a tradeoff between prudent exploitation and rapid reproduction-a life history tradeoff between longevity and fecundity. Other tradeoffs among components of parasite fitness also influence virulence. For example, competition among parasite genotypes favors rapid growth to achieve greater relative success within the host. Rapid growth may, however, lower the total productivity of the local group by overexploiting the host, which is a potentially renewable food supply. This is a problem of kin selection and group selection. I summarize models of parasite virulence with the theoretical tools of life history analysis, kin selection, and epidemiology. I then apply the theory to recent empirical studies and models of virulence. These applications, to nematodes, to the extreme virulence of hospital epidemics, and to bacterial meningitis, show the power of simple life history theory to highlight interesting questions and to provide a rich array of hypotheses. These examples also show the kinds of conceptual mistakes that commonly arise when only a few components of parasite fitness are analysed in isolation. The last part of the article connects standard models of parasite virulence to diverse topics, such as the virulence of bacterial plasmids, the evolution of genomes, and the processes that influenced conflict and cooperation among the earliest replicators near the origin of life.

Animals↗
PubMed1995

Estimating parametric survival model parameters in gerontological aging studies: methodological problems and insights.

Studies of the biology of aging (both experimental and evolutionary) frequently involve the estimation of parameters arising in various multi-parameter survival models such as the Gompertz or Weibull distribution. Standard parameter estimation methodologies, such as maximum likelihood estimation (MLE) or nonlinear regression (NLR), require knowledge of the actual life spans or their explicit algebraic equivalents in order to provide reliable parameter estimates. Many fundamental biological discussions and conclusions are highly dependent upon accurate estimates of these survival parameters (this has historically been the case in the study of genetic and environmental effects on longevity and the evolutionary biology of aging). In this article, we examine some of the issues arising in the estimation of gerontologic survival model parameters. We not only address issues of accuracy when the original life-span data are unknown, we consider the accuracy of the estimates even when the exact life spans are known. We examine these issues as applied to known experimental data on diet restriction and we fit the frequently used, two-parameter Gompertzian survival distribution to these experimental data. Consequences of methodological misuse are demonstrated and subsequently related to the values of the final parameter estimates and their associated errors. These results generalize to other multiparametric distributions such as the Weibull, Makeham, and logistic survival distributions.

Aging↗
PubMed1997

Prebiotic phosphorus chemistry reconsidered.

The available evidence indicates that the origin of life on Earth certainly occurred earlier than 3.5 billion years ago and perhaps substantially earlier. The time available for the chemical evolution which must have preceded this event is more difficult to estimate. Both endogenic and exogenic contributions to chemical evolution have been considered; i.e., from chemical reactions in a primitive atmosphere, or by introduction in the interiors of comets and/or meteorites. It is argued, however, that the phosphorus chemistry of Earth's earliest hydrosphere, whether primarily exogenic or endogenic in origin, was most likely dominated by compounds less oxidized than phosphoric acid and its esters. A scenario is presented for the early production of a suite of reactive phosphonic acid derivatives, the properties of which may have foreshadowed the later appearance of biophosphates.

Atmosphere↗
PubMed2005

Early environmental origins of neurodegenerative disease in later life.

Parkinson disease (PD) and Alzheimer disease (AD), the two most common neurodegenerative disorders in American adults, are of purely genetic origin in a minority of cases and appear in most instances to arise through interactions among genetic and environmental factors. In this article we hypothesize that environmental exposures in early life may be of particular etiologic importance and review evidence for the early environmental origins of neurodegeneration. For PD the first recognized environmental cause, MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), was identified in epidemiologic studies of drug abusers. Chemicals experimentally linked to PD include the insecticide rotenone and the herbicides paraquat and maneb; interaction has been observed between paraquat and maneb. In epidemiologic studies, manganese has been linked to parkinsonism. In dementia, lead is associated with increased risk in chronically exposed workers. Exposures of children in early life to lead, polychlorinated biphenyls, and methylmercury have been followed by persistent decrements in intelligence that may presage dementia. To discover new environmental causes of AD and PD, and to characterize relevant gene-environment interactions, we recommend that a large, prospective genetic and epidemiologic study be undertaken that will follow thousands of children from conception (or before) to old age. Additional approaches to etiologic discovery include establishing incidence registries for AD and PD, conducting targeted investigations in high-risk populations, and improving testing of the potential neurologic toxicity of chemicals.

Age Factors↗
PubMed2002

Chromosomal aberrations in peripheral lymphocytes of children as biomarkers of environmental exposure and life style.

The original purpose of our study was to determine if the detection of chromosomal aberrations in peripheral lymphocytes of children might be used as a biomarker of environmental pollution and life style. We compared the results of cytogenetic analyses performed in children and adolescents in the periods 1984-1993 and 1994-1999, in a total of 3402 subjects. The frequency of aberrant cells (AB.C.) markedly decreased in the period 1994-1999 compared with the period 1984-1993. The decreases in AB.C. were significant in the age groups 7-15 and 16-19 years: 1.63% AB.C. versus 1.14% AB.C. and 2.02% AB.C. versus 1.08% AB.C., respectively (P<0.01). No difference in the frequency of AB.C. was observed in newborns. Based on our experience, we believe that monitoring the spontaneous level of chromosomal aberrations in children over 5 year periods may be used to examine the general changes in environmental pollution in larger geographic areas.

Adolescent↗
PubMed2003

Exchange of meteorites (and life?) between stellar systems.

It is now generally accepted that meteorite-size fragments of rock can be ejected from planetary bodies. Numerical studies of the orbital evolution of such planetary ejecta are consistent with the observed cosmic ray exposure times and infall rates of these meteorites. All of these numerical studies agree that a substantial fraction (up to one-third) of the ejecta from any planet in our Solar System is eventually thrown out of the Solar System during encounters with the giant planets Jupiter and Saturn. In this paper I examine the probability that such interstellar meteorites might be captured into a distant solar system and fall onto a terrestrial planet in that system within a given interval of time. The overall conclusion is that it is very unlikely that even a single meteorite originating on a terrestrial planet in our solar system has fallen onto a terrestrial planet in another stellar system, over the entire period of our Solar System's existence. Although viable microorganisms may be readily exchanged between planets in our solar system through the interplanetary transfer of meteoritic material, it seems that the origin of life on Earth must be sought within the confines of the Solar System, not abroad in the galaxy.

Evolution, Planetary↗
PubMed2005

Hormonal aspects in the causation of human breast cancer: epidemiological hypotheses reviewed, with special reference to nutritional status and first pregnancy.

Epidemiology of breast cancer has identified early age at menarche, late first pregnancy, low parity and late menopause as risk factors, but in addition genetic factors, height, weight and living in western countries play a significant role. The international variation in incidence is almost exclusively due to non-genetic factors. Hypotheses in prevention-oriented research are reviewed: 1. obesity-related oestrogen production as a stimulus of the tumour in postmenopausal women; 2. nutritional status and energy expenditure during puberty and adolescence, developed for fertility and fecundity and extended later to breast cancer; 3. reproductive life during early adulthood, age at first pregnancy and its specific effects on breast tissues. The message of preventability of breast cancer is that mammary epithelial differentiation should come early. Our insight concerning events in puberty and early adulthood can be consolidated in one concept on the risk of extended proliferation of breast epithelium during early adulthood in the absence of full differentiation induced by pregnancy. The combined effects of Western-type nutrition, lack of exercise and Western-type women's emancipation sets the stage for breast cancer already at a young age. Since it is unlikely that emancipated women in affluent societies will return to the original life-style of getting pregnant as soon as it is biologically possible, a novel daring way of protection has to be considered. Could a "Breast Differentiation Pill" be developed to offer protection?

Age Factors↗
PubMed1999

Constructing an RNA world.

A popular theory of life's origins states that the first biocatalysts were not made of protein but were made of RNA or a very similar polymer. Experiments are beginning to confirm that the catalytic abilities of RNA are compatible with this 'RNA world' hypothesis. For example, RNA can synthesize short fragments of RNA in a template-directed fashion and promote formation of peptide, ester and glycosidic linkages. However, no known activity fully represents one presumed by the 'RNA world' theory, and reactions such as oxidation and reduction have yet to be demonstrated. Filling these gaps would place the hypothesis on much firmer ground and provide components for building minimal forms of RNA-based cellular life.

RNA↗
PubMed2002

Microbial arsenic: from geocycles to genes and enzymes.

Arsenic compounds have been abundant at near toxic levels in the environment since the origin of life. In response, microbes have evolved mechanisms for arsenic resistance and enzymes that oxidize As(III) to As(V) or reduce As(V) to As(III). Formation and degradation of organoarsenicals, for example methylarsenic compounds, occur. There is a global arsenic geocycle, where microbial metabolism and mobilization (or immobilization) are important processes. Recent progress in studies of the ars operon (conferring resistance to As(III) and As(V)) in many bacterial types (and related systems in Archaea and yeast) and new understanding of arsenite oxidation and arsenate reduction by respiratory-chain-linked enzyme complexes has been substantial. The DNA sequencing and protein crystal structures have established the convergent evolution of three classes of arsenate reductases (that is classes of arsenate reductases are not of common evolutionary origin). Proposed reaction mechanisms in each case involve three cysteine thiols and S-As bond intermediates, so convergent evolution to similar mechanisms has taken place.

Arsenate Reductases↗
PubMed2005

Key science questions from the second conference on early Mars: geologic, hydrologic, and climatic evolution and the implications for life.

In October 2004, more than 130 terrestrial and planetary scientists met in Jackson Hole, WY, to discuss early Mars. The first billion years of martian geologic history is of particular interest because it is a period during which the planet was most active, after which a less dynamic period ensued that extends to the present day. The early activity left a fascinating geological record, which we are only beginning to unravel through direct observation and modeling. In considering this time period, questions outnumber answers, and one of the purposes of the meeting was to gather some of the best experts in the field to consider the current state of knowledge, ascertain which questions remain to be addressed, and identify the most promising approaches to addressing those questions. The purpose of this report is to document that discussion. Throughout the planet's first billion years, planetary-scale processes-including differentiation, hydrodynamic escape, volcanism, large impacts, erosion, and sedimentation-rapidly modified the atmosphere and crust. How did these processes operate, and what were their rates and interdependencies? The early environment was also characterized by both abundant liquid water and plentiful sources of energy, two of the most important conditions considered necessary for the origin of life. Where and when did the most habitable environments occur? Did life actually occupy them, and if so, has life persisted on Mars to the present? Our understanding of early Mars is critical to understanding how the planet we see today came to be.

Evolution, Planetary↗
PubMed1995

The prebiotic role of adenine: a critical analysis.

Adenine plays an essential role in replication in all known living systems today, and is prominent in many other aspects of biochemistry. It occurs among the products of oligomerization of HCN. These circumstances have stimulated the idea that adenine was a component in a replication system that was present at the start of life. Such replicators have included not only RNA, but also a number of simpler RNA-like alternatives which utilize a simpler backbone. Despite these encouraging indicators, a consideration of the chemical properties of adenine reveals reasons that disfavor its participation in such a role. These properties include the following: (1) Adenine synthesis requires HCN concentrations of at least 0.01 M. Such concentrations would be expected only in unique circumstances on the early Earth. Adenine yields are low in prebiotic simulations, and if a subsequent high-temperature hydrolysis step is omitted, the reported yield does not represent adenine itself, but 8-substituted adenines and other derivatives. (2) Adenine is susceptible to hydrolysis (the half life for deamination at 37 degrees C, pH 7, is about 80 years), and to reaction with a variety of simple electrophiles, forming a multiplicity of products. Its accumulation would not be expected over a geological time scale, and its regioselective incorporation into a replicator appears implausible. (3) The adenine-uracil interaction, which involves two hydrogen bonds (rather than three, as in guanine-cytosine pairing) is weak and nonspecific. Pairing of adenine with many other partners has been observed with monomers, synthetic oligonucleotides and in RNA. The hydrogen-bonding properties of adenine appear inadequate for it to function in any specific recognition scheme under the chaotic conditions of a prebiotic soup. New and fundamental discoveries in the chemistry of adenine would be needed to reverse this perception. An alternative and attractive possibility is that some other replicator preceeded RNA (or RNA-like substances) in the origin of life.

Adenine↗