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Results for “Continuous Evolution”

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PubMed1991

Patterns of DNA methylation--evolutionary vestiges of foreign DNA inactivation as a host defense mechanism. A proposal.

The proposals in this review are based on experimental work on the integration of foreign DNA in mammalian cells, on the establishment of specific de novo patterns of DNA methylation, and on the inhibition of transcription by the sequence-specific methylation of promoter sequences. It is suggested that eukaryotic cells have developed several mechanisms of defense against the uptake, integration, and continued expression of foreign DNA. In the course of evolution and continuing at present, cells have been exposed to foreign DNA, entire genomes or fragments of them. A particularly problematic organ system in that respect must be digestive tract in higher organisms. The defense mechanisms are thought to be the following: (i) degradation and/or excretion of foreign DNA; (ii) excision and loss of previously integrated DNA from the host genome; (iii) targeted inactivation of foreign genes by sequence-specific methylation. Genes whose products could be advantageous to the transformed cells can somehow be selectively excluded from this silencing mechanism. In part, the specificity of de novo methylation must reside in the DNA methyltransferase systems of the host cell. However, nucleotide sequence, structure, and chromatin arrangement in the foreign DNA could also play an important role. Since defense processes must have been activated many times in evolution, patterns of DNA methylation as they can be observed today, may represent vestiges of evolution, i.e. the sum total of selective de novo methylations, possibly demethylations, and mutations.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2003

The dual biological identity of human beings and the naturalization of morality.

The last two centuries have been the centuries of the discovery of the cell evolution: in the XIX century of the germinal cells and in the XX century of two groups of somatic cells, namely those of the brain-mind and of the immune systems. Since most cells do not behave in this way, the evolutionary character of the brain-mind and of the immune systems renders human beings formed by t wo different groups of somatic cells, one with a deterministic and another with an indeterministic (say Darwinian) behavior. An inherent consequence is that of the generation, during ontogenesis, of a dual biological identity. The concept of the dual biological identity may be used to explain the Kantian concept of the two metaphysical worlds, namely of the causal necessity and of the free will (Azzone, 2001). Two concepts, namely those of complex adaptive systems (CAS) and of emergence (Holland, 2002), are useful tools for understanding the mechanisms of adaptation and of evolution. The concept of complex adaptive systems indicates that living organisms contain series of stratified components, denoted as building blocks, forming stratified layers of increasing complexity. The concept of emergence implies the use of repeating patterns and of building blocks for the generation of structures of increasing levels of complexity, structures capable of exchanging communications both in the top-down and in the bottom-up direction. Against the concept of emergence it has been argued that nothing can produce something which is really new and endowed of causal efficacy. The defence of the concept of emergence is based on two arguments. The first is the interpretation of the variation-selection mechanism as a process of generation of information and of optimization of free energy dissipation in accord with the second principle of thermodynamics. The second is the objective evidence of the cosmological evolution from the Big Bang to the human mind and its products. Darwin has defended the concept of the continuity of evolution. However evolution should be considered as continuous when there is no increase of information and as discontinuous when there is generation of new information. Examples of such generation of information are the acquisition of the innate structures for language and the transition from absence to presence of morality. There are several discontinuity thresholds during both phylogenesis and ontogenesis. Morality is a relational property dependent on the interactions of human beings with the environment. Piaget and Kohlberg have shown that the generation of morality during childhood occurs through several stages and is accompanied by reorganization of the child mental organization. The children respect the conventions in the first stage and gradually generate their autonomous morality. The transition from absence to presence of morality, a major adaptive process, then, not only has occurred during phylogenesis but it occurs again in every human being during ontogenesis. The religious faith does not provide a logical justification of the moral rules (Ayala, 1987) but rather a psychological and anthropological justification of two fundamental needs of human beings: that of rendering Nature an understandable entity, and that of increasing the cooperation among members of the human societies. The positive effects of the altruistic genes in the animal societies are in accord with the positive effects of morality for the survival and development of the human societies.

Adaptation, Biological↗

PubMed1998

MR state of the art.

Magnetic resonance imaging is undergoing continual and progressive evolution. To make a high quality examination, some requirements are mandatory, such as high spatial and contrast resolution to identify lesions and high temporal resolution to characterize them. We review the most important new magnetic resonance technologies, both those which are already available and used in clinical practice and those which are still to be developed. We analyze such technologic and methodolgic features as magnetic field strength, gradients, surface coils, echoplanar imaging, fat suppression techniques and magnetization transfer, contrast agents, automatic injectors, image postprocessing, computer assisted diagnosis, magnetic resonance-guided biopsy and spectroscopy. All these factors are in continuous evolution and new technologies anticipate, in the near future, faster examinations with very high spatial and contrast resolution, with magnetic resonance-guided cytologic and histologic aspiration biopsies, as well as spectroscopic studies of previously identified lesions. To perform a correct, state-of-the-art magnetic resonance examination of the breast, we need high strength gradients with high slew rate and bilateral coils. Finally, we discuss new technologies and methods which will increase the accuracy of magnetic resonance studies of the breast, improving image quality and decreasing execution time. Thus, magnetic resonance spectroscopy, allowing in vivo biochemical tissue analysis, seems to have high potentials; even though they are still difficult to define, the technique is sure to have major diagnostic impact also in monitoring the results to different treatments.

Biopsy↗

PubMed2000

RNA shape space topology.

The distinction between continuous and discontinuous transitions is a long-standing problem in the theory of evolution. Because continuity is a topological property, we present a formalism that treats the space of phenotypes as a (finite) topological space, with a topology that is derived from the probabilities with which one phenotype is accessible from another through changes at the genotypic level. The shape space of RNA secondary structures is used to illustrate this approach. We show that evolutionary trajectories are continuous if and only if they follow connected paths in phenotype space.

Models, Genetic↗

PubMed1981

Regional continuity in Australasian Pleistocene hominid evolution.

A reconstruction of the Indonesian male Homo erectus specimen Sangiran 17 reveals a suite of features that suggests regional morphological continuity in Australasia during the middle and late Pleistocene. Characteristics reflecting a morphological clade are established through a comparison with the males from Kow Swamp, the late Pleistocene Australian site with the largest number of hominid specimens. It is argued that the "center and edge" hypothesis could account for the initial appearance of regional variation, and that a dynamic model of geneflow and opposing selection provides the mechanism that maintained a long-standing dynamic clinal equilibrium in this area.

Animals↗

PubMed1995

Muto ergo sum. Hepatitis B and the forces of evolution.

The hepatitis B virus (HBV) polymerase has no editing function and thus frequently transcribes its template incorrectly to result in viral variants that go under the name of "mutants." These mutants may be viewed as part of a continuing Darwinian evolution of HBV with some survival benefit. They also result in unusual extrahepatic manifestations of HBV infection, which will doubtless continue to divert the hepatologist.

Biological Evolution↗

PubMed1997

The role of immaturity in human development.

The possibility that infants' and young children's immature behaviors and cognitions are sometimes adaptive is explored and interpreted in terms of evolutionary theory. It is argued that developmental immaturity had an adaptive role in evolution and continues to have an adaptive role in human development. The role of developmental retardation in human evolution is discussed, followed by an examination of the relation between humans' extended childhood and brain plasticity. Behavioral neoteny, as exemplified by play, is examined, as are some potentially adaptive aspects of infants' perception and cognition that limit the amount of information they can process. Aspects of immature cognition during early childhood that may have some contemporaneous adaptive value are also discussed. It is proposed that viewing immaturity as sometimes adaptive to the developing child alters how children and their development are viewed.

Adaptation, Psychological↗

PubMed1978

Family practice in evolution: progress, problems and projections.

Family practice has developed in direct response to the public need for primary care with the elements of comprehensiveness, continuity and accessibility. This specialty represents a re-emphasis of the generalist role in medicine, with particular concern for the family as the unit of care. Since the American Board of Family Practice was formed nine years ago, the first phase of development has been completed. Teaching programs in family medicine have been effectively established at undergraduate and graduate levels throughout the country in both university and community settings. Refinement of teaching programs and initiation of a strong ongoing research effort are now required. The continued successful evolution of family practice as a foundation of primary care in the United States is essential to extend the highest possible quality of care to the entire population at a cost that can be afforded in a society with limited resources for health care.

Curriculum↗

PubMed1989

Chromosomal inversion patterning and population differentiation in a young insular species, Drosophila silvestris.

The recently evolved Hawaiian species Drosophila silvestris has a subdivided population structure and shows great spatial heterogeneity in chromosome inversion distributions and frequencies within its extremely limited geographic range. Pattern analysis of the 11 chromosomal polymorphisms in the context of the recently discovered morphological and behavioral divergence within the species has elucidated the history of the chromosomal differentiation. We identify four chronological groups of inversions and their probable sites of origin. Spread of the derived "3-row" bristle morphotype on the Hilo side of the Island of Hawaii has been accompanied by the acquisition of six new inversion polymorphisms. Three phylogenetically old inversions show correlations with altitude, and there are multiple cross-correlations between inversions on the same and different chromosomes, reflecting complex interaction systems. Quantification of the genetic population structure of D. silvestris by hierarchical F statistics reveals a dramatic level of genetic differentiation for an evolutionarily new species of such restricted range. This level exceeds that of older, continental Drosophila species. There is, however, minimal concordance between the chromosomal variation and the morphological-behavioral discontinuity, a consequence of the extensive cytological variation within each morphotype. Such a fragmented gene pool favors the rapid evolution and continued divergence of this insular species.

Animals↗

PubMed2004

A non-adaptationist perspective on evolution of genomic complexity or the continued dethroning of man.

A new, non-adaptationist theory of evolution of genomic complexity was recently proposed by Lynch and Conery. This concept holds that increase in complexity seen in eukaryotic genomes is a 'syndrome' caused by increase in genome entropy, which is inevitably triggered by reduction of population size. Here, I discuss the definitions of genomic entropy and complexity and the evidence supporting the entropic theory of genome complexity evolution, including new observations on concordant gain and loss of genes and introns in eukaryotic genomes. I further consider the far-reaching biological and philosophical implications of this theory.

Adaptation, Biological↗

PubMed2006

In vivo molecular evolution reveals biophysical origins of organismal fitness.

In nature, evolution occurs through the continuous adaptation of a population to its environment. At the molecular level, adaptive changes in protein sequence and expression impact organismal fitness and, consequently, dictate population dynamics. Here, we have used a "weak link" method to favor variations in one gene, allowing adaptation to thermostability to be studied in molecular detail as bacteria were grown continuously for approximately 1500 generations. Surprisingly, only six mutant alleles, representing less than 1% of the possible missense mutations, were observed, suggesting a highly constrained molecular landscape during protein evolution. The changes in organismal fitness were linked directly to incremental increases in enzyme stability and activity maxima and corresponded to the narrow temperature ranges where each mutant enjoyed success within the overall population. Thus, continuous evolution of a single gene permits a quantitative approach that extends from the phenotypes of the microbial populations to their underlying biophysical basis.

Adenylate Kinase↗

PubMed1981

Differential Light Responses of Photosynthesis by Triazine-resistant and Triazine-susceptible Senecio vulgaris Biotypes.

Studies were conducted to determine a physiological basis for competitive differences between Senecio vulgaris L. biotypes which are either resistant or susceptible to triazine herbicides. Net carbon fixation of intact leaves of mature plants was higher at all light intensities in the susceptible biotype than in the resistant biotype. Quantum yields measured under identical conditions for each biotype were 20% lower in the resistant than in the susceptible biotype. Oxygen evolution in continuous light measured in stroma-free chloroplasts was also higher at all light intensities in the susceptible biotype than in the resistant biotype. Oxygen evolution in response to flashing light was measured in stroma-free chloroplasts of both biotypes. The steady-state yield per flash of resistant chloroplasts was less than 20% that of susceptible chloroplasts. Susceptible chloroplasts displayed oscillations in oxygen yield per flash typically observed in normal chloroplasts, whereas the pattern of oscillations in resistant chloroplasts was noticeably damped. It is suggested that modification of the herbicide binding site which confers s-triazine resistance may also affect the oxidizing side of photosystem II, making photochemical electron transport much less efficient. This alteration has resulted in a lowered capacity for net carbon fixation and lower quantum yields in whole plants of the resistant type.

Journal Article↗

PubMed1995

Transcriptional noise and the evolution of gene number.

Several proposals are made to explain the apparent increase in complexity of certain lineages during evolution. The proposals (not made in this order) are: (1) that gene number is a valid measure of biological complexity; (2) that gene number has not increased continuously during evolution, but has risen in discrete steps; (3) that two of the biggest steps occurred at the transition from prokaryotes to eukaryotes and the transition from invertebrates to vertebrates; (4) that these steps were made possible by 'systemic' changes in the way that genetic information is managed in the genome; (5) that the ability to silence inappropriate promoters is the primary limitation on gene number; (6) that the invention of nucleosomes (and perhaps the nuclear membrane) facilitated the evolution of eukaryotes from prokaryotic ancestors; (7) that the spread of low density methylation throughout the genome facilitated the evolution of vertebrates from invertebrate ancestors.

Animals↗

PubMed1981

Evolution of photosynthetic reaction centers.

The common ancestor of all photosynthetic prokaryotes and organelles contained chlorophyll (Chl) a. All green and purple photosynthetic bacteria descended from a common bacteriochlorophyll (Bchl) a-containing ancestor which diverged from the Chl a line. Separate PS-I and PS-II reaction centers may have evolved before the appearance of Bchl a. When the transition to Bchl a occurred, the resultant organism contained two types of reaction center, "PS-I" and "PS-II." One line of development eliminated "PS-II" and evolved into the green bacteria. The other line eliminated "PS-I" and became the purple bacteria. In the Chl a-containing organisms the evolution of PS-II continued until oxygen evolution was achieved.

Bacteria↗

PubMed1991

Complications of urinary tract reconstruction.

Urinary tract reconstruction has benefited a vast number of patients with dysfunctional lower urinary tracts caused by congenital abnormalities, previous surgery, or both. Reconstructive efforts have been innovative and continue to evolve. With this evolution, new complications continue to appear, and in order to minimize the risk to the patient, we must recognize our previous lessons. Appropriate patient selection is essential in achieving a successful outcome in this group. The patient's neurologic status, urologic anatomy, renal function, and motivation are also important factors in choosing the appropriate patient and correct surgical approach. Close follow-up remains the single most important element in assuring long-term well-being for most of these patients.

Foreign-Body Migration↗

PubMed2006

Developing and sustaining a web-based library newsletter.

The JEFFLINE Forum, Scott Library's attempt to revive the traditional library newsletter by employing the technical advantages and increasing presence of the Web, debuted in October 1999. The fifth anniversary of the Forum was a good time to look back at its evolution and to examine some of the challenges inherent in developing and sustaining a library newsletter. By identifying the most successful strategies, and reflecting on the lessons learned along way, the authors hope to continue the evolution of the Forum and help to ensure the viability of the library newsletter.

Humans↗

PubMed1997

The hospital evolution to discharge planning automation.

An automated discharge planning system generates significant productivity benefits to hospitals committing to the process. It also allows full interactive communication to track patients at any level in the continuum of care. Not every hospital today is capable of operating in a network environment. In addition, many ECOs are not currently equipped to participate in the discharge planning process using personal computers. Capital investment costs present an obstacle to some providers contemplating participation in the process of interactive discharge patient information exchange through the continuum. Yet external pressures continue to mount for improved healthcare process productivity. As a result, both hospitals and extended care organizations seem likely to increasingly rely on automation of the discharge planning process in order to operate and compete effectively as the healthcare industry continues its evolution.

Admitting Department, Hospital↗

PubMed1956

The effect of chloramphenicol on deoxyribonucleic acid synthesis and the development of resistance to ultraviolet irradiation in E. coli infected with bacteriophage T2.

To elucidate the role of protein synthesis in DNA formation, E. coli R2 infected with phage T2 was studied as a model, employing chloramphenicol to inhibit protein synthesis. The following results were obtained. 1. Chloramphenicol inhibited protein synthesis but not synthesis of nucleic acids in uninfected bacteria. 2. Studies of the effect of chloramphenicol on phage maturation indicated a delay of 2 minutes between time of addition and cessation of phage growth. 3. The increase of DNA in phage-infected bacteria was completely suppressed by the addition of chloramphenicol within 2 minutes following infection. Addition at later times showed progressively less inhibitory action depending upon the time interval, and addition after the 10th or 12th minute showed no appreciable effect on DNA synthesis despite the cessation of intracellular phage formation and protein synthesis. 4. When chloramphenicol was added to infected cells the increase of resistance to UV stopped within 2 minutes, whether or not DNA synthesis continued. Thus evolution of resistance paralleled the rate of DNA synthesis achieved, but not the amount of DNA accumulated. 5. We conclude that in infected bacteria, protein synthesis is necessary to initiate DNA synthesis but is not essential for its continuation. The resistance to UV that characterizes infected cells near the midpoint of the latent period is not due to accumulation of DNA, but depends on some chloramphenicol-sensitive process (probably protein synthesis) completed at about the time the rate of DNA synthesis becomes maximal.

Bacteriophage T4↗