Resource-dependent selection.

This paper presents a resource-dependent viability selection differential equation model of continuously reproducing diploid population with two alleles at one locus for a single limiting resource. This model assumes that the genotypic fitness is only a function of the limiting resource. The conditions that the interior equilibrium point of the system exists are that the heterozygote fitness is positive and the homozygote fitness is negative, or the heterozygote fitness is negative and the homozygote fitness is positive at the point. The sufficient and necessary conditions of locally asymptotical stability of the interior equilibrium point are that the heterozygote fitness is positive at the point, or the locally asymptotically stable equilibrium corresponds to the point at which the level of the limiting resource is locally minimized on the zero mean fitness curve, f = 0.     

Natural selection. VII. History and interpretation of kin selection theory

Kin selection theory is a kind of causal analysis. The initial form of kin selection ascribed cause to costs, benefits and genetic relatedness. The theory then slowly developed a deeper and more sophisticated approach to partitioning the causes of social evolution. Controversy followed because causal analysis inevitably attracts opposing views. It is always possible to separate total effects into different component causes. Alternative causal schemes emphasize different aspects of a problem, reflecting the distinct goals, interests and biases of different perspectives. For example, group selection is a particular causal scheme with certain advantages and significant limitations. Ultimately, to use kin selection theory to analyse natural patterns and to understand the history of debates over different approaches, one must follow the underlying history of causal analysis. This article describes the history of kin selection theory, with emphasis on how the causal perspective improved through the study of key patterns of natural history, such as dispersal and sex ratio, and through a unified approach to demographic and social processes. Independent historical developments in the multivariate analysis of quantitative traits merged with the causal analysis of social evolution by kin selection.     

Contig selection in physical mapping.

In physical mapping, one orders a set of genetic landmarks or a library of cloned fragments of DNA according to their position in the genome. Our approach to physical mapping divides the problem into smaller and easier subproblems by partitioning the probe set into independent parts (probe contigs). For this purpose we introduce a new distance function between probes, the averaged rank distance (ARD) derived from bootstrap resampling of the raw data. The ARD measures the pairwise distances of probes within a contig and smoothes the distances of probes across different contigs. It shows distinct jumps at contig borders. This makes it appropriate for contig selection by clustering. We have designed a physical mapping algorithm that makes use of these observations and seems to be particularly well suited to the delineation of reliable contigs. We evaluated our method on data sets from two physical mapping projects. On data from the recently sequenced bacterium Xylella fastidiosa, the probe contig set produced by the new method was evaluated using the probe order derived from the sequence information. Our approach yielded a basically correct contig set. On this data we also compared our method to an approach which uses the number of supporting clones to determine contigs. Our map is much more accurate. In comparison to a physical map of Pasteurella haemolytica that was computed using simulated annealing, the newly computed map is considerably cleaner. The results of our method have already proven helpful for the design of experiments aimed at further improving the quality of a map.     

Natural selection. III. Selection versus transmission and the levels of selection

George Williams defined an evolutionary unit as hereditary information for which the selection bias between competing units dominates the informational decay caused by imperfect transmission. In this article, I extend Williams' approach to show that the ratio of selection bias to transmission bias provides a unifying framework for diverse biological problems. Specific examples include Haldane and Lande's mutation-selection balance, Eigen's error threshold and quasispecies, Van Valen's clade selection, Price's multilevel formulation of group selection, Szathmáry and Demeter's evolutionary origin of primitive cells, Levin and Bull's short-sighted evolution of HIV virulence, Frank's timescale analysis of microbial metabolism and Maynard Smith and Szathmáry's major transitions in evolution. The insights from these diverse applications lead to a deeper understanding of kin selection, group selection, multilevel evolutionary analysis and the philosophical problems of evolutionary units and individuality.     

Sexual selection, natural selection and copulatory patterns in male primates.

Complex copulatory patterns, involving multiple brief intromissions or prolonged single intromissions (PI) occur most frequently among primate species in which females mate with a number of partners (multimale and dispersed mating systems). However, the PI pattern is also confined almost exclusively to arboreal primates - to either smaller-bodied, cryptic, nocturnal species or much larger diurnal forms. Predation pressures may have limited the evolution of the PI pattern, particularly where small-bodied diurnal primates or terrestrial forms are concerned. The available evidence indicates that both sexual selection and natural selection may have influenced the evolution of copulatory patterns.     

In vitro selection and extended culture of antigen-specific T lymphocytes. II. Mechanisms of selection.

Functional selection of antigen-specific T lymphocytes can be achieved by culturing thymus-dependent (T) lymphocytes from immunized guinea pigs on "monolayers" of antigen-pulsed adherent peritoneal exudate cells (PEC) from nonimmune syngeneic donors. Several aspects of the in vitro selection of T lymphocyte-rich peritoneal exudate lymphocytes (PEL) were studied. It was shown that irradiated adherent PEC were equivalent to nonirradiated adherent PEC in supporting selection cultures, indicating that the lymphocytes harvested at the end of the selection culture derive from the immune donors of the PEL and not from the nonimmune donor of the adherent PEC. The relative importance of specific adherence and specific proliferation for achieving selection was determined by comparing the degree of selection obtained when nonadherent cells were discarded at 24 hr with that noted when the discard step was omitted. It was found that omitting the discard step markedly diminished the degree of selection. On the other hand, blocking proliferation with specific alloantisera after the discard step did not diminish the degree of selection, although it did diminish the cell yield. Thus, specific adherence to antigen-pulsed PEC appeared to be critical in the selection culture procedure. An estimate of the degree of enrichment obtained by the selection culture procedure was obtained by culturing selected cells in an excess of nonprimed PEL, so that auxiliary cells would not be limiting. Under these conditions, it appeared that selected cells were enrichied from 4- to 10-fold in antigen-responsive cells with respect to the initial cell population.     

Theories of social selection in human populations.

Using Huntington disease, mental retardation, and schizophrenia, it has been shown that two individuals with identical genotypes or phenotypes have different fitnesses because of affected nuclear family members. Such fitness interaction seems to occur because of cultural and social reactions due to the presence of affected individuals, and the interaction has been termed "social selection." Without assuming any specific genetic control for the social behavior, we can study the effect of social behavior on the incidence of a genetic disease.     

Variances of selection differentials in normal samples.

Standardized variances of selection differentials are defined in general and then considered in detail for the case of directional selection on the basis of normally distributed test scores. Symmetry properties, bounds and asymptotic values for the variances are derived. The results are used to investigate the variance of response to selection.