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Results for “Continuous Evolution”

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PubMed1988

Deleterious mutations and the evolution of sexual reproduction.

The origin and maintenance of sexual reproduction continues to be an important problem in evolutionary biology. If the deleterious mutation rate per genome per generation is greater than 1, then the greater efficiency of selection against these mutations in sexual populations may be responsible for the evolution of sex and related phenomena. In modern human populations detrimental mutations with small individual effects are probably accumulating faster than they are being eliminated by selection.

Animals↗

PubMed1993

Will man need the vestibular system in generations to come? A slightly heretical review.

Some people are of the opinion, that man's evolution reached a plateau when he became self-aware. Thus, the argument goes, he was enabled to reflect on what happened to him and what he did to his environment. Subsequent to that man would think ahead to the consequences of his actions and thereby actively shape his future to ensure optimal survival of his species. And this state of course no longer could be called evolution in the classical sense. Need one comment on the vanity of the hope for such a state? Let us assume then, that the evolution of man has not ended, but will continue and that man has barely a clue, yet, as to the direction it may lead.

Adaptation, Biological↗

PubMed2006

The phylogenetic distribution of metazoan microRNAs: insights into evolutionary complexity and constraint.

How complex body plans evolved in animals such as fruit flies and vertebrates, as compared to the relatively simple jellyfish and sponges, is not known, given the similarity of developmental genetic repertoires shared by all these taxa. Here, we show that a core set of 18 microRNAs (miRNAs), non-coding RNA molecules that negatively regulate the expression of protein-coding genes, are found only in protostomes and deuterostomes and not in sponges or cnidarians. Because many of these miRNAs are expressed in specific tissues and/or organs, miRNA-mediated regulation could have played a fundamental evolutionary role in the origins of organs such as brain and heart--structures not found in cnidarians or sponges--and thus contributed greatly to the evolution of complex body plans. Furthermore, the continuous acquisition and fixation of miRNAs in various animal groups strongly correlates both with the hierarchy of metazoan relationships and with the non-random origination of metazoan morphological innovations through geologic time.

Animals↗

PubMedDate not supplied

[Complete nitrification in soil columns perfused with nitrite].

Four columns of the same soil were put under the continuous flow of a NaNO2 solution [50 ppm N], so as to follow the evolution of nitrification. The soil, the columns as well as the solution continuous flow regulating system, were prepared as in the previous experiments. The columns, with the exception of No1 (control), contained also the following substances: No2 and 4: 2% de CaCO3 and No3 and 4:0.0015% SO - 4-S. Since the eight day of perfusion all the effluents had an important concentration of nitrate (Figure 1), exceeding in them, the sum of [No-2-N] an [NO-3-N] (Table 1) the concentration of th NO-2-N of the perfusion solution. Finally, the [NO-2-N] was reduced importantly in the effluents, and the (NO-3N), in all of them, stabilized itself as values nearing 50 ppm. Its suggested that at the beginning of the experiment, an endogenous source of NO-2 was functioning, which could explain the observed phenomenon, and that later it ceased to do so. The populational density of NO-2 oxidizers increased, during the experiment, 49 times (Table 2). An increase was also measured in the populational density of NH+4 oxidizers, which amounted to 41 times. This later fact contributes to support the existence of an endogenous provision of NO-2 during the initial part of the experiment.

Bacteria↗

PubMed1995

Mutual policing and repression of competition in the evolution of cooperative groups.

Evolutionary theory has not explained how competition among lower level units is suppressed in the formation of higher-level evolutionary units. For example, the key problem of early evolution is small, individual replicators formed cooperative groups of sufficient complexity to allow accurate copying of the genetic material. The puzzle is why parasites did not subvert the formation of cells by obtaining benefits from the group without contributing to shared traits that enhance reproduction. These parasites would outcompete other replicators within the cell, disrupting reproductive fairness among subunits and destroying the functional coherence of the group. A similar problem arose at a later evolutionary stage with the orderly mendelian segregation of subunits (chromosomes) within cells, and reproductive fairness continued to be a problem in the evolution of insect and human societies. Here I present a simple model to show how reproductive fairness evolves among subunits to create functional coherence and higher-level units. Self-restraint, which evolves according to the kin-selection coefficient of relatedness, is not sufficient: mutual policing and enforcement of reproductive fairness are also required for the evolution of increasing social complexity.

Biological Evolution↗

PubMed1990

Evolution of sequences encoding the principal neutralization epitope of human immunodeficiency virus 1 is host dependent, rapid, and continuous.

The principal neutralization epitope of human immunodeficiency virus 1 is localized in the third variable (V3) domain of the external envelope and has been shown to bind isolate-specific antibodies. Therefore, the extent of variation within the nucleic acid sequence encoding this epitope was studied in DNA directly obtained from peripheral blood mononuclear cells of six children and their plasma donor. This revealed that the quasi-species distribution of sequences obtained after cloning varied from recipient to recipient and that the distance from the donor sequences increased over time. V3 nucleotide evolution rates averaged 9.5 x 10(-3) per site per year for silent sites and 11.4 x 10(-3) per site per year for nonsilent sites (vs. 9.7 and 9.8 x 10(-3) per site per year for a control region 5' adjacent to the V3 region) and, although individual differences were observed, did not correlate with the serum antigen levels or disease progression. Sequences of both the epitope coding region itself (V3) and the control region upstream diverted more from the donor sequence among children not progressing to AIDS than among children progressing to AIDS. The evolution of V3 sequences is apparently host dependent, rapid, and independent of the level of antigen expression.

Acquired Immunodeficiency Syndrome↗

PubMed2003

Evolution of function in (beta/alpha)8-barrel enzymes.

The (beta/alpha)(8)-barrel is the most common fold in structurally characterized enzymes. Whether the functionally diverse enzymes that share this fold are the products of either divergent or convergent evolution (or both) is an unresolved question that will probably be answered as the sequence databases continue to expand. Recent work has examined natural, designed, and directed evolution of function in several superfamilies of (beta/alpha)(8)-barrel containing enzymes.

Animals↗

PubMed2000

Impulsive and Varying Injection in Gamma-Ray Burst Afterglows.

The standard model of gamma-ray burst afterglows is based on synchrotron radiation from a blast wave produced when the relativistic ejecta encounters the surrounding medium. We reanalyze the refreshed shock scenario, in which slower material catches up with the decelerating ejecta and reenergizes it. This energization can be done either continuously or in discrete episodes. We show that such a scenario has two important implications. First, there is an additional component coming from the reverse shock that goes into the energizing ejecta. This persists for as long as the reenergization itself, which could extend for up to days or longer. We find that during this time the overall spectral peak is found at the characteristic frequency of the reverse shock. Second, if the injection is continuous, the dynamics will be different from that in constant energy evolution and will cause a slower decline of the observed fluxes. A simple test of the continuously refreshed scenario is that it predicts a spectral maximum in the far-infrared or millimeter range after a few days.

Journal Article↗

PubMed2001

A generalized adaptive dynamics framework can describe the evolutionary Ultimatum Game.

Adaptive dynamics describes the evolution of games where the strategies are continuous functions of some parameters. The standard adaptive dynamics framework assumes that the population is homogeneous at any one time. Differential equations point to the direction of the mutant that has maximum payoff against the resident population. The population then moves towards this mutant. The standard adaptive dynamics formulation cannot deal with games in which the payoff is not differentiable. Here we present a generalized framework which can. We assume that the population is not homogeneous but distributed around an average strategy. This approach can describe the long-term dynamics of the Ultimatum Game and also explain the evolution of fairness in a one-parameter Ultimatum Game.

Adaptation, Physiological↗

PubMed2000

Continuous haemofiltration in the intensive care unit.

Continuous renal replacement therapy (CRRT) was first described in 1977 for the treatment of diuretic-unresponsive fluid overload in the intensive care unit (ICU). Since that time this treatment has undergone a remarkable technical and conceptual evolution. It is now available in most tertiary ICUs around the world and has almost completely replaced intermittent haemodialysis (IHD) in some countries. Specially made machines are now available, and venovenous therapies that use blood pumps have replaced simpler techniques. Although, it remains controversial whether CRRT decreases mortality when compared with IHD, much evidence suggests that it is physiologically superior. The use of CRRT has also spurred renewed interest in the broader concept of blood purification, particularly in septic states. Experimental evidence suggests that this is a promising approach to the management of septic shock in critically ill patients. The evolution and use of CRRT is likely to continue and grow over the next decade.

Brain Edema↗

PubMed1985

Mitochondrial DNA-like sequences in the human nuclear genome. Characterization and implications in the evolution of mitochondrial DNA.

Thirty-three phage clones carrying DNAs homologous to human mitochondrial DNA (mtDNA) were isolated from two independently constructed human gene libraries, and the region and extent of homology of mtDNA-like sequences carried by these clones were examined in hybridization experiments. Each phage clone contained DNA sequences homologous to various parts of the mtDNA and the extent of homology differed from clone to clone. From the efficiency of the library screening, it was estimated that human nuclear DNA contains at least several hundred copies of mtDNA-like fragments. Four clones carrying nuclear DNA sequences homologous to the mitochondrial Unidentified Reading Frame (URF) 4 and URF5 regions were chosen for further studies, and their structures were analyzed by DNA sequencing. Comparison of these mtDNA-like sequences with that of mtDNAs of several mammalian species revealed conservation of a part of the structures present in direct ancestral mtDNAs. The mtDNA fragments seem to have been continuously integrated into mammalian nuclear DNA during evolution.

Bacteriophage lambda↗

PubMed2004

Continuous renal replacement technology: from adaptive devices to flexible multipurpose machines.

OBJECTIVE: To review the evolution of technologies in the development of renal replacement therapies. DATA SOURCES: Articles and published reviews on renal replacement therapies. SUMMARY OF REVIEW: Continuous arterio-venous haemofiltration (CAVH) was the first continuous renal replacement technique capable of overcoming the traditional haemodialysis-related side effects, making possible the treatment of critically ill patients safely and with less physiological instability. The evolution of technology and the progress experienced in intensive care units (ICUs) has made it possible to start renal replacement therapy programs in the absence of a chronic dialysis facility or a trained nephrological team. Initial limitations and draw-backs of CAVH, stimulated the ICU staff to explore new avenues for better therapy. Extracorporeal therapies are today a routine experience in the ICUs: continuous renal replacement therapies are a broadly accepted treatment for acute renal failure. Furthermore, alternative indications for extracorporeal blood circulation (e.g. sepsis, liver failure, congestive heart failure, drug intoxications, hyperthermia, immuno-mediated syndromes) are becoming more and more popular. The ideal machine has yet to be completed, but progress has occurred and has opened a new era for critical care nephrology and the further expansion of blood purification technology in the ICU. CONCLUSIONS: Technical advances in renal replacement therapies have increased their functionality (i.e. used in hepatic failure, sepsis, cardiac failure and immuno-mediated syndromes), are easier to operate and have less side-effects compared with their standard extracorporeal counterparts. Further improvements may see them become a routine part in the management of the critically ill patient.

Journal Article↗

PubMed1994

"Simulated molecular evolution" or computer-generated artifacts?

1. The authors define a function with value 1 for the positive examples and 0 for the negative ones. They fit a continuous function but do not deal at all with the error margin of the fit, which is almost as large as the function values they compute. 2. The term "quality" for the value of the fitted function gives the impression that some biological significance is associated with values of the fitted function strictly between 0 and 1, but there is no justification for this kind of interpretation and finding the point where the fit achieves its maximum does not make sense. 3. By neglecting the error margin the authors try to optimize the fitted function using differences in the second, third, fourth, and even fifth decimal place which have no statistical significance. 4. Even if such a fit could profit from more data points, the authors should first prove that the region of interest has some kind of smoothness, that is, that a continuous fit makes any sense at all. 5. "Simulated molecular evolution" is a misnomer. We are dealing here with random search. Since the margin of error is so large, the fitted function does not provide statistically significant information about the points in search space where strings with cleavage sites could be found. This implies that the method is a highly unreliable stochastic search in the space of strings, even if the neural network is capable of learning some simple correlations. 6. Classical statistical methods are for these kind of problems with so few data points clearly superior to the neural networks used as a "black box" by the authors, which in the way they are structured provide a model with an error margin as large as the numbers being computed.7. And finally, even if someone would provide us with a function which separates strings with cleavage sites from strings without them perfectly, so-called simulated molecular evolution would not be better than random selection.Since a perfect fit would only produce exactly ones or zeros,starting a search in a region of space where all strings in the neighborhood get the value zero would not provide any kind of directional information for new iterations. We would just skip from one point to the other in a typical random walk manner.

Amino Acid Sequence↗

PubMed2005

Specification and patterning of neural crest cells during craniofacial development.

Craniofacial evolution is considered fundamental to the origin of vertebrates and central to this process was the formation of a migratory, multipotent cell population known as the neural crest. The number of cell types that arise from the neural crest is truly astonishing as is the number of tissues and organs to which the neural crest contributes. In addition to forming melanocytes as well as many neurons and glia in the peripheral nervous system, neural crest cells also contribute much of the cartilage, bone and connective tissue of the face. These multipotent migrating cells are capable of self renewing decisions and based upon these criteria are often considered stem cells or stem cell-like. Rapid advances in our understanding of neural crest cell patterning continue to shape our appreciation of the evolution of neural crest cells and their impact on vertebrate craniofacial morphogenesis.

Animals↗

PubMed2002

The evolution of the Marie Stopes electrocautery no-scalpel vasectomy procedure.

OBJECTIVE: To review the evolution of the procedure, the reoperation rate and efficacy data for vasectomies performed in Marie Stopes centres during the periods 1990-1994 and 1995-1999. DESIGN: Retrospective review of re-operation rates and primary and secondary failures during the periods 1990-1994 and 1995-1999. SETTING: Marie Stopes vasectomy centres in the UK. PARTICIPANTS: A total of 41 123 men undergoing vasectomy. RESULTS: The re-operation rate for the period 1990-1994 was 0.7% and fell to 0.46% for 1995-1999. The reported pregnancy rate fell from 1 in 1429 procedures for the period 1990-1994 to 1 in 2804 for 1995-1999. CONCLUSION: The results show that vasectomy has had a low failure rate well below that of other methods of birth control. The outcome data continue to improve over time with the evolution of improved techniques and surgical expertise.

Electrocoagulation↗

PubMed1977

Cold Shock Syndrome in Anacystis nidulans.

The phenomenon of cold shock in Anacystis nidulans has been explored further in terms of loss of viability and immediate and subsequent metabolic effects. Cold shock was observed also in two closely related strains in which unsaturated fatty acid contents are also known to be low and temperature-dependent. Loss of viability was maximum for cells grown at temperatures above 40 C (<10(-4) survivors after 5 min at 0 C) but became negligibly small for cells grown below 34 C. Development of the cold-sensitive condition after transfer 25 --> 39 C was slow and comparable to rate of growth; development of the insensitive condition after transfer 39 --> 25 C was rapid, implying rapid in situ alteration. An immediate metabolic effect, observed as a decrease in rate of photosynthetic O(2) evolution measured at growth temperature, was less severe than loss of viability. Continued light incubation under growth conditions led to slow decay in rate of O(2) evolution accompanied by loss of membrane chlorophyll. The multiple effects which comprise the cold shock syndrome appear to be membrane-related phenomena and thereby provide an experimental probe of normal membrane function.

Journal Article↗

PubMed2004

Bacteroid proline catabolism affects N(2) fixation rate of drought-stressed soybeans.

In prior work, we observed that soybean (Glycine max L. cv Merr.) seeds inoculated with a mutant Bradyrhizobium japonicum strain unable to catabolize Pro (Pro dehydrogenase(-) [ProDH(-)]) resulted in plants that, when forced to depend on N(2) fixation as the sole source of nitrogen and subjected to mild drought stress, suffered twice as large a loss in seed yield as did plants inoculated with the parental strain. Here, we used a continuous gas flow system to measure H(2) evolution as a function of time and leaf water potential (Psi(L)). Since one H(2) is produced for every N(2) fixed as an obligate part of the mechanism of N(2) fixation, these measurements serve as the basis for continuous monitoring of the N(2) fixation rate. In five replicate experiments, the slope of the decline in N(2) fixation rate in response to water stress was always greater for plants inoculated with the mutant strain unable to catabolize Pro or take up H(2) (ProDH(-), hup(-)) than it was for plants inoculated with the parental strain (ProDH(+), hup(-)). In aggregate, the probability that this difference occurred by chance alone was 0.005. In combination with the earlier result, this is consistent with bacteroid catabolism of Pro synthesized in response to mild drought stress having a positive impact on N(2) fixation rate and seed yield.

Bradyrhizobium↗

PubMed1984

Origin of sex.

The competitive advantage of sex consists in being able to use redundancy to recover lost genetic information while minimizing the cost of redundancy. We show that the major selective forces acting early in evolution lead to RNA protocells in which each protocell contains one genome, since this maximizes the growth rate. However, damages to the RNA which block replication and failure of segregation make it advantageous to fuse periodically with another protocell to restore reproductive ability. This early, simple form of genetic recovery is similar to that occurring in extant segmented single stranded RNA viruses. As duplex DNA became the predominant form of the genetic material, the mechanism of genetic recovery evolved into the more complex process of recombinational repair, found today in a range of species. We thus conclude that sexual reproduction arose early in the evolution of life and has had a continuous evolutionary history. We cite reasons to reject arguments for gaps in the evolutionary sequence of sexual reproduction based on the presumed absence of sex in the cyanobacteria. Concerning the maintenance of the sexual cycle among current organisms, we take care to distinguish between the recombinational and outbreeding aspects of the sexual cycle. We argue that recombination, whether it be in outbreeding organisms, self-fertilizing organisms or automictic parthenogens, is maintained by the advantages of recombinational repair. We also discuss the role of DNA repair in maintaining the outbreeding aspects of the sexual cycle.

Biological Evolution↗