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PubMedDate not supplied

Androgens in human evolution. A new explanation of human evolution.

Human evolution consists of chronological changes in gene regulation of a continuous and relatively stable genome, activated by hormones, the production of which is intermittently affected by endogenous and exogenous forces. Periodic variations in the gonadal androgen, testosterone, and the adrenal androgen, dehydroepiandrosterone (DHEA), significantly participated in all hominid transformations. The hominid characteristics of early Australopithecines are primarily a result of increased testosterone. The first significant cold of the early Pleistocene resulted in an increase in DHEA that simultaneously produced Homo and the robust Australopithecines. Subsequent Pleistocene climatic changes and differential reproduction produced changes in DHEA and testosterone ratios that caused extinction of the robust Australopithecines and further changes and continuation of Homo. Changes in testosterone and DHEA produce allometric and behavioral changes that are identifiable and vigorous in modern populations.

Adolescent↗
PubMed2003

The evolution of genomic base composition in bacteria.

Guanine plus cytosine (GC) content ranges broadly among bacterial genomes. In this study, we explore the use of a Brownian-motion model for the evolution of GC content over time. This model assumes that GC content varies over time in a continuous and homogeneous manner. Using this model and a maximum-likelihood approach, we analyzed the evolution of GC content across several bacterial phylogenies. Using three independent tests, we found that the observed divergence in GC content was consistent with a homogeneous Brownian-motion model. For example, similar rates of GC content evolution were inferred in several different bacterial subclades, indicating that there is relatively little rate heterogeneity in GC content evolution over broad evolutionary time scales. We thus argue that the homogeneous Brownian-motion model provides a good working model for GC content evolution. We then use this model to determine the overall rate of GC content evolution among eubacteria. We also determine the time frame over which GC content remains similar in related taxa, using a flexible definition for "similarity" in GC content so that, depending on the context, more or less stringent criteria may be applied. Our results have implications for models of sequence evolution, including those used for phylogenetic reconstruction and for inferring unusual changes in GC content.

Bacteria↗
PubMedDate not supplied

Group dynamics within long-term continuing education programs.

Nursing educators have responded to the need for continuing education by developing a variety of programs ranging in length from half-day seminars to several months of intensive study. Although books and articles have been written about nurses returning to school for baccalaureate degrees and the ensuing expectations, changes, and needs involved in this process, the literature revealed little information on how students, families, and faculty "live" a long-term continuing education (CE) experience. This article will examine the evolution of students into well-defined groups. The stages of group process, development of norms, assumption of roles within the groups, and factors related to conflicts are discussed. Methods used to reduce conflict and facilitate the movement of the groups to the resolution stage are presented in order to assist instructors involved in long-term CE programs.

Adult↗
PubMed1996

Unusual features of the urodele genome: do they have a role in evolution and development?

Urodeles are amongst the organisms with the highest C-values. They provide a useful system for studies of genome organization at both the chromosomal and the molecular level. In this contribution we discuss the general features of "excess" DNA in urodeles and emphasize that the urodele genome is in a state of plasticity. That fluidity is due to various molecular mechanisms which are involved in its continuous turnover. The implications of this fluid, "excess DNA" for evolution and/or development are considered.

Animals↗
PubMed2004

Kinetic analysis of a model for double substrate cycling: highly amplified ADP (and/or ATP) quantification.

A mathematical description has been made of an enzyme amplification mechanism involving the coupling of two substrate cycles. In this amplification system one of the noncycling products of a first substrate cycle acts as a trigger molecule that continuously feeds a second substrate cycle. Time-concentration equations describing the evolution of the species involved in the system have been obtained. The model is illustrated by the quantification of nanomolar levels of ADP (and/or ATP) in a continuous assay involving the enzymes L-lactate dehydrogenase and L-lactate oxidase to cycle the pyruvate accumulated in a first enzymatic cycle constituted by the enzymes pyruvate kinase and hexokinase. Progress curves were seen to be parabolic, and, according to the kinetic equations obtained, followed second-order polynomials of the reaction time. Mathematical equations for minimizing the cost of the assays are also given. The model is applicable to the amplified analytical determination of low levels of a metabolite or an enzyme activity, and its amplification capacity, together with the simplicity of determining kinetic parameters, enable it to be employed in enzyme immunoassays to increase the magnitude of the measured response.

Adenosine Diphosphate↗
PubMed2000

Genome evolution in polyploids.

Polyploidy is a prominent process in plants and has been significant in the evolutionary history of vertebrates and other eukaryotes. In plants, interdisciplinary approaches combining phylogenetic and molecular genetic perspectives have enhanced our awareness of the myriad genetic interactions made possible by polyploidy. Here, processes and mechanisms of gene and genome evolution in polyploids are reviewed. Genes duplicated by polyploidy may retain their original or similar function, undergo diversification in protein function or regulation, or one copy may become silenced through mutational or epigenetic means. Duplicated genes also may interact through inter-locus recombination, gene conversion, or concerted evolution. Recent experiments have illuminated important processes in polyploids that operate above the organizational level of duplicated genes. These include inter-genomic chromosomal exchanges, saltational, non-Mendelian genomic evolution in nascent polyploids, inter-genomic invasion, and cytonuclear stabilization. Notwithstanding many recent insights, much remains to be learned about many aspects of polyploid evolution, including: the role of transposable elements in structural and regulatory gene evolution; processes and significance of epigenetic silencing; underlying controls of chromosome pairing; mechanisms and functional significance of rapid genome changes; cytonuclear accommodation; and coordination of regulatory factors contributed by two, sometimes divergent progenitor genomes. Continued application of molecular genetic approaches to questions of polyploid genome evolution holds promise for producing lasting insight into processes by which novel genotypes are generated and ultimately into how polyploidy facilitates evolution and adaptation.

Evolution, Molecular↗
PubMed2006

Sexual conflict and the evolution of female preferences for indicators of male quality.

Males and females have opposing interests when it comes to the honesty of signals used in mate choice. The existence of this sexual conflict has long been acknowledged, but its consequences have not been fully investigated. By applying adaptive dynamics methods and individual-based computer simulations to a standard model for good-genes sexual selection, we show that sexual conflict over condition-dependent signaling can prevent the handicap process from ever attaining an evolutionary equilibrium. We outline the parameter conditions and properties of the underlying genetics conducive to nonequilibrium behavior and discuss the potential of such behavior to explain the elaboration and frequent phylogenetic loss of sexually selected traits. We also evaluate its consequences for well-established insights of sexual selection theory previously shown to apply when female mating preference and male ornament expression do converge on stable equilibrium levels. Contrary to equilibrium expectation, a continual change of condition-dependent signaling enables the evolution of a costly preference for a pure epistatic indicator and the evolution of preferences for redundant signals or a large number of independent ornaments. We thus conclude that seemingly general results of sexual selection theory, insofar as these are based on equilibrium considerations, do not extend to cases where nonequilibrium behavior occurs.

Adaptation, Biological↗
PubMed1985

Current issues in prevention of infective endocarditis.

Prevention of infective endocarditis continues to concern health care providers in many specialties. The well-known lack of primary clinical trials in this area is not expected to change. Therefore, the evolution of recommendations and practice must be based on theoretic considerations and continuing assessment of secondary sources of information. Recent developments include a report of 52 cases in which antibiotic prophylaxis for infective endocarditis was attempted but appeared to fail. Most of these patients had undergone dental procedures after oral penicillin prophylaxis, with subsequent development of streptococcal endocarditis. In two thirds, the organism was sensitive to the antibiotic used. Notably, the most common underlying cardiac lesion among these patients was mitral valve prolapse. However, two recent independent analyses have concluded that providing endocarditis prophylaxis for all patients with mitral valve prolapse during procedures that might cause bacteremia would not be cost-effective. This is primarily because mitral valve prolapse is common and endocarditis is relatively rare, resulting in an adverse risk-benefit ratio. Parenteral prophylaxis for mitral valve prolapse might even cause a net loss of life from anaphylaxis. On the other hand, for the individual patient or physician, the reassurance provided by attempted prophylaxis with oral penicillin can be purchased at low cost and low risk. Very few cases of infective endocarditis have been reported after gastrointestinal and other endoscopic procedures; most of these do not need antibiotic coverage. Prophylactic antibiotics should be restricted to those situations in which both the procedure and the underlying cardiac condition seem to pose significant risk, for example, endoscopic sclerotherapy of esophageal varices in patients with prosthetic heart valves. Newly revised recommendations have been issued by the Medical Letter, the American Heart Association, and the American Dental Association. These regimens are shorter and simpler than earlier versions.

Anti-Bacterial Agents↗
PubMed2003

The evolution of external and internal implant/abutment connections.

The indications for implant dentistry continue to increase, enabling the restoration of partially and totally edentulous patients with greater success and predictability. Recent goals for implant dentistry include simplifying the involved procedures, reducing the duration of therapy for the patient and clinician, and enabling the use of conventional prosthodontic techniques for implant-supported restorations. This article reviews key developments in implantology and highlights the various design characteristics of internal abutment connection implants, demonstrating their clinical application in a detailed case presentation.

Dental Abutments↗
PubMed1993

The Robinow (fetal face) syndrome: a continuing puzzle.

The history of the Robinow (fetal face) syndrome and the evolution of the phenotype are presented. Non-specific and syndrome-specific abnormalities are listed, discussed and illustrated. Existence of an autosomal dominant and an autosomal recessive type has been well documented. The two forms can be distinguished phenotypically. Hypogenitalism, especially micropenis, is a constant feature in males, while females show only hypoplasia of clitoris and labia minora and are functionally normal. No biochemical or molecular anomaly has been identified.

Abnormalities, Multiple↗
PubMedDate not supplied

The maximum lactate clearance: a new concept to approach the endurance level of an athlete.

The purpose of this study is to present a mathematical model based on physiological observations which describes the evolution of the blood lactate concentration ([LA-]) versus the oxygen uptake (VO2) during a continuous graded exercise test. This model is based on several assumptions: 1) [LA-] reflects the balance between the rates of appearance and disappearance of the lactate in the blood compartment; 2) VO2 measured at the end of each step, is a linear function of the power output and thus of the time; 3) the appearance rate of lactate into the blood is an exponential function of VO2; 4) the rate of disappearance is a saturable process which can be modelized by Michaelis-Menten kinetics; 5) the volume of distribution of lactate in the blood compartment is a constant during exercise. The parameters used in this model correspond to the integration of several biochemical and physiological phenomenons. The originality of this approach is to express the rate of lactate appearance and disappearance versus VO2 rather than time. Whatever the general pattern of the data, the fitted curve gives always very good results. Especially, the theoretical curve fits the decrease in [LA-] usually observed during the first steps of such an exercise. From the computed parameters the evolution of lactate clearance during a continuous graded exercise test may be modelized. A strong relationship exists between the level of endurance training and the maximum lactate clearance (Clmax) reached during the exercise test. The VO2 for Clmax is an indicator of the shift of the relationship [LA-]-VO2. Then, we propose to use the maximum lactate clearance which is individually determined, to characterize the endurance level of an athlete.

Adolescent↗
PubMed2005

A new machine for continuous renal replacement therapy: from development to clinical testing.

A new continuous renal replacement therapy machine has been designed to fulfill the expectations of nephrologists and intensivists operating in the common ground of critical care nephrology. The new equipment is called Prismaflex and it is the natural evolution of the PRISMA machine that has been utilized worldwide for continuous renal replacement therapy in the last 10 years. The authors performed a preliminary alpha-trial to establish the usability, flexibility and reliability of the new device. Accuracy was also tested by recording various operational parameters during different intermittent and continuous renal replacement modalities during 62 treatments. This article will describe our first experience with this new device and touch upon the historic and technologic background leading to its development.

Clinical Trials as Topic↗
PubMed2005

Pathophysiology of posttraumatic temporal lobe lesions.

BACKGROUND: Posttraumatic parenchymal lesions in the temporal lobe may cause neurologic deterioration. An analysis was made of the natural evolution of this type of lesion, with emphasis on its 2 components: hemorrhage (hyperdense on computed tomography [CT]), and edema and necrosis (hypodense on CT). The clinical repercussions were studied, and the factors that might influence such evolution were investigated. METHODS: Forty head-injured patients with temporal lobe lesions admitted within 12 hours after the injury were selected in a prospective manner. Computed tomography scans were systematically repeated within the first 36 hours and at 7 and 30 days postinjury. Factors such as interval between injury and the first CT scan, age, velocity of the injury, alcohol consumption, coagulation abnormalities, and the presence of decompressive measures were compared between the patients that had enlargement of the hemorrhage and those who did not. Increase in hypodensity was compared with that in hyperdensity. RESULTS: Fourteen patients showed enlargement of the hemorrhage. In all cases but one, the interval between injury and admission was 3 hours or less. Other factors had no statistical significance as predisposing causes for such enlargement. In approximately half of the cases, the hypodense component increased in the first 36 hours and continued increasing until the end of the first week. Evolution of the hypodense component was not dependent on behavior of the hemorrhage, surgical drainage, or diameter of the hemorrhagic lesion. CONCLUSIONS: The natural evolution of the hyperdense component of temporal lobe lesions was to enlarge within the first few hours after the injury. Edema and necrosis developed more slowly and with no significant clinical manifestations.

Age Factors↗
PubMed2000

The formation and early evolution of the Milky Way galaxy.

Recent observations indicate that the Milky Way may have formed by aggregation of gas and stars from a reservoir of preexisting small galaxies in the local universe. The process probably began more than 12 billion years ago with material of different original angular momentum following two separate evolutionary lines, one into the slowly rotating halo and central bulge and the other into the rapidly rotating disk. The existence of distinct thick and thin disks shows that continuing mergers of satellite galaxies likely also determined the early evolution of the main structural component of the luminous Galaxy.

Astronomical Phenomena↗