Showing papers on "Selection (genetic algorithm) published in 1984"

Ecological determinants of genetic structure in plant populations

Abstract: Plant populations are not randomly arranged assemblages of genotypes but are structured in space and time (2, 29, 49, 58, 84, 112). This structure may be manifested among geographically distinct populations, within a local group of plants, or even in the progeny of individuals. Genetic structure results from the joint action of mutation, migration, selection, and drift, which in tum must operate within the historical and biological context of each plant species. Ecological factors affecting reproduction and dispersal are likely to be particularly important in determining genetic structure (2, 31, 58). Reproduction is the process that translates the current genotypic array into that of subsequent generations, while the dispersal of pollen and seeds determines the postreproductive pattems of gene dispersion within and among populations. Although the concept of genetic structure has been used in various ways (58, 130, 154), we limit our definition to the nonrandom distribution of alleles or genotypes in space or time and disregard genome organization and meiotic processes that can also affect allele and genotype frequencies. Because of the limited mobility of plants, their genetic structure implies spatial structure, or the actual physical distribution of individuals. While spatial pattems often have genetic implications, nonrandom genetic pattems can exist without a nonrandom distribution of individuals. Conversely, a population may have a nonrandom spatial distribution without any accompanying genetic structure. Spatial and genetic patterns are often assumed to result from environmental heterogeneity and differential selection pressures (22, 53, 131, 132). Selection is a ubiquitous feature of natural populations; it alters gene and

Cross-Validation of Regression Models

Abstract: A methodolgy for assessment of the predictive ability of regression models is presented. Attention is given to models obtained via subset selection procedures, which are extremely difficult to evaluate by standard techniques. Cross-validatory assessments of predictive ability are obtained and their use illustrated in examples.

On the measurement of natural and sexual selection: theory.

Abstract: The aim of this paper is to illustrate an approach to the empirical measurement of selection that is directly related to formal evolutionary theory. Recent field studies have demonstrated that it is feasible to measure fitness in natural populations. The most successful studies have yielded accurate tallies of survivorship, mating success and fertility (e.g., Tinkle, 1965; Howard, 1979; Downhower and Brown, 1980; Lennington, 1980; Kluge, 1981; Clutton-Brock et al., 1982). Despite this success, no concensus has been reached on how to analyze the data and relate them to evolutionary theory. We present here a mode of data analysis that describes selection in useful, theoretical terms, so that field or experimental results will have a tangible relationship to equations for evolutionary change. Multivariate, polygenic theory (Lande, 1979, 1980, 1981; Bulmer, 1980) is particularly useful as a conceptual framework because it is concerned with the evolution of continuously distributed traits such as those commonly studied in laboratory and field situations. Multivariate equations have been used for many years by plant and animal breeders in order to impose selection and predict its impact (Smith, 1936; Hazel, 1943; Dickerson et al., 1954, 1974; Yamada, 1977), but this quantitative genetic theory has only recently been applied to evolutionary problems. Definitions and Aims. -It is critical to distinguish between selection and evolutionary response to selection (Fisher, 1930; Haldane, 1954). Selection causes observable changes within a generation in the means, variances and covariances of phenotypic distributions. Thus selection can be described in purely phenotypic terms without recourse to the inheritance of characters. In contrast, evolutionary response to selection, for example, the change in phenotypic mean from one generation to the next, certainly does depend on inheritance. In the following sections we show how knowledge of inheritance can be combined with purely phenotypic measures of selection to predict evolutionary response to selection. By distinguishing between selection and response to selection we can measure selection on characters whose mode of inheritance may be unknown and make prediction of evolutionary response a separate issue. Thus knowledge of inheritance is essential for complete

The Selection of Disputes for Litigation

Abstract: THIS paper addresses the relationship between litigated disputes and disputes settled before or during litigation. The specification of this relationship is important for the analysis both of the legal system and of the influence of the legal system on society. Virtually all systematic knowledge of the legal system derives from studies of appellate cases. Appellate cases, of course, provide the most direct view of doctrinal developments in the law. Few scholars today, however, are content to study doctrinal developments alone without regard to the broader influence of legal rules on social affairs. Appellate cases may tell us which disputes courts find troublesome and which they find easy to decide. But this doctrinal information discloses very little about how legal rules affect the behavior of those subject to them or affect the generation of legal disputes themselves. If all legal disputes, or even a random sample of these disputes, were tried to judgment and then appealed, the inference from legal rules to social behavior would be straightforward. The facts of appellate cases

Truth in advertising: the kinds of traits favored by sexual selection

Abstract: Ever since sexual selection was first described by Darwin (1871), biologists have recognized the importance of the phenomenon but have had difficulty in understanding how it operates. Sexual selection is that special form of natural selection which is responsible for the evolution of traits that promote success in competition for mates. It is particularly important in polygamous breeding systems in which individuals of one sex, usually female, invest many more resources in gametes and often also in parental care, and individuals of the other sex, usually males, compete to mate with these females (Bateman 1948; Trivers 1972). Sexual selection can take two forms. On the one hand it can favor the evolution of traits, such as those related to fighting ability, which increase success in direct competition with other males for mates. On the other hand, it can lead to the evolution of characteristics, such as those involved in courtship displays, which make males more attractive to females. Although strikingly sexually dimorphic characteristics, such as the antlers of deer, the plumes of birds of paradise, and the elaborate displays of bowerbirds have been attributed to sexual selection, the precise mechanisms responsible for the evolution of these traits have remained the subject of much debate. There are two main hypotheses. Fisher's (1930) runaway selection model proposes that sexual selection will favor females that choose mates on the basis of any trait that confers an initial survival or reproductive advantage. This process will continue, resulting in simultaneous exaggeration of the trait and enhanced female choice, until the trait reduces survival of males to the point that this outweighs the advantages of increased reproductive success. This model assumes that the advantages and disadvantages conferred by the trait are confined to the sex (male) that expresses it, and that sexual selection is a special form of directional selection that ultimately tends to oppose natural selection for traits related to survival. Zahavi's (1975) handicap hypothesis also proposes that sexual selection favors the exaggeration of traits which promote male reproductive success at the expense of survival. Females choose mates with such traits because their demonstrated ability to survive despite such a handicap indicates the overall fitness of their genotypes. Under this model both male and female offspring tend to inherit

The Evolutionary Significance of Genetic Diversity: Ecological, Demographic and Life History Correlates

Abstract: The evolutionary significance of genetic diversity of proteins in nature remains controversial despite the numerous protein studies conducted electrophoretically during the last two decades. Ironically, the discovery of extensive protein polymorphisms in nature (reviewed by Lewontin, 1974; Powell, 1975; Selander, 1976; Nevo 1978, 1983b; Hamrick et al., 1979; Nelson and Hedgecock, 1980), did not resolve the disagreement between the die ho torn ou s explanatory models of selection (e.g., Ayala, 1977; Milkman, 1978; Clarke, 1979; Wills, 1981) versus neutrality (Kimura, 1968; Kimura and Chta, 1971; Nei, 1975; and modifications in Kimura, 1979atb). The more general problem of the relative importance of the evolutionary forces interacting in genetic population differentiation at the molecular levels of proteins and DNA, i.e., mutation, migration, natural selection and genetic drift, remains now as enigmatic as ever.

The quantitative genetics of polyphagy in an insect herbivore. ii. genetic correlations in larval performance within and among host plants.

Abstract: Because the overall evolution of the phenotype is a composite of direct and correlated responses to selection, the evolutionary trajectories of genetically correlated characters are fundamentally interdependent (Hazel, 1943; Falconer, 1981 Ch. 19). The effects of genetic correlations on phenotypic evolution are twofold. First, genetic covariance can influence the rate of response to selection. If characters simultaneously selected to increase are influenced by genes with positively correlated effects, the response to selection will be more rapid for the pair than for either character selected separately until the underlying genes are fixed. Conversely, negative genetic correlations among characters selected to increase can slow their rate of simultaneous evolution from that predicted by the amount of genetic variation which exists for each character separately (Dickerson, 1955; Antonovics, 1976; Lande, 1982b). Secondly, genetic correlations can affect the direction of evolution in suites of cliaracters such that traits no longer evolve directly toward their individual optima. In some cases, traits may even be drawn away from their optima for many generations due to selection on genetically correlated characters (Lande, 1980; Via and Lande, unpubl.). The manifold evolutionary effects of genetic correlations dictate a multivariate approach to the study of the quantitative genetic basis of evolution (Lande, 1979, 1980, 1982a, 1982b). Inmost non-

Choosing Between the Sample-Selection Model and the Multi-Part Model

Abstract: Hay and Olsen (1984) incorrectly argue that a multi-part model, the two-part model used in Duan et al. (1982,1983), is nested within the sample-selection model. Their proof relies on an unmentioned restrictive assumption that cannot be satisfied. We provide a counterexample to show that the propensity to use medical care and the level of expense can be positively associated in the two-part model, contrary to their assertion. The conditional specification in the multi-part model is preferable to the unconditional specification in the selection model for modeling actual (v. potential) outcomes. The selection model also has poor statistical and numerical properties and relies on untestable assumptions. Empirically the multi-part estimators perform as well as or better than the sample selection estimator for the data set analyzed in Duan et al. (1982, 1983).

Sélection of subsets of regression variables

Abstract: On etudie divers algorithmes de calcul en considerant seulement les modeles lineaires et le critere des moindres carres

Selection of Subsets of Regression Variables

Abstract: On etudie divers algorithmes de calcul en considerant seulement les modeles lineaires et le critere des moindres carres

Generalized Selection and Ranking: Sorted Matrices

Abstract: A more general version of the well-known selection problem is formulated, in which constraints on the input set are allowed. Selection (and also ranking) problems are solved optimally for the broad class of inputs constrained to be collections of matrices with sorted rows and sorted columns.The characterization of problem complexity includes an asymptotically significant dependency on the rank of the solution element.

The theory of evolution and dynamic systems mathematical aspects of selection

Abstract: Preface Part I. Selection Dynamics and Population Genetics: A Discrete Introduction: 1. The biological background 2. The Hardy-Weinberg law 3. Selection and the fundamental theorem 4. Mutation and recombination Part II. Growth Rates and Ecological Models: An ABC on ODE: 5. The ecology of populations 6. The logistic equation 7. Lotka-Volterra equations for predator prey-systems 8. Lotka-Volterra equations for two competing species 9. Lotka-Volterra equations for more than two populations Part III. Test Tube Evolution and Hypercycles: A Prebiotic Primer: 10. Prebiotic evolution 11. Branching processes and the complexity threshold 12. Catalytic groth f selfreproducing molecules 13. Permanence and the evolution of hypercycles Part IV. Strategies and Stability: An Opening in Game Dynamics: 14. Some aspects of sociobiology 15. Evolutionarily stable strategies 16. Game dynamics 17. Asymmetric conflicts Interlude.

Recurrent patterns of natural selection in a population of Darwin's finches

Abstract: The adaptive significance of morphological traits can be assessed by measuring and identifying the forces of selection acting on them Boag and Grant documented directional selection in a small population of Darwin's medium ground finches, Geospiza fortis, on I Daphne Major, Galapagos, in 1977 Large beak and body size were favoured at a time of diminishing food supply and high adult mortality We show here that in two subsequent periods of moderate to high adult mortality (1980 and 1982), the population was subject to the same selection We have used a recently developed technique to ascertain the targets of direct selection Beak depth and body weight were commonly under direct selection to increase but, surprisingly, beak width was directly selected to decrease, over all three periods of mortality The results have implications for our understanding of evolutionary change in morphological traits of Darwin's finches

Selection by consequences

Abstract: Human behavior is the joint product of (i) contingencies of survival responsible for natural selection, and (ii) contingencies of reinforcement responsible for the repertoires of individuals, including (iii) the special contingencies maintained by an evolved social environment. Selection by consequences is a causal mode found only in living things, or in machines made by living things. It was first recognized in natural selection: Reproduction, a first consequence, led to the evolution of cells, organs, and organisms reproducing themselves under increasingly diverse conditions. The behavior functioned well, however, only under conditions similar to those under which it was selected.Reproduction under a wider range of consequences became possible with the evolution of processes through which organisms acquired behavior appropriate to novel environments. One of these, operant conditioning, is a second kind of selection by consequences: New responses could be strengthened by events which followed them. When the selecting consequences are the same, operant conditioning and natural selection work together redundantly. But because a species which quickly acquires behavior appropriate to an environment has less need for an innate repertoire, operant conditioning could replace as well as supplement the natural selection of behavior.Social behavior is within easy range of natural selection, because other members are one of the most stable features of the environment of a species. The human species presumably became more social when its vocal musculature came under operant control. Verbal behavior greatly increased the importance of a third kind of selection by consequences, the evolution of social environments or cultures. The effect on the group, and not the reinforcing consequences for individual members, is responsible for the evolution of culture.

On selection among groups with heterogeneous variance

Abstract: Problems of making selection decisions among animals from several environmental groups with heterogeneous variance are discussed. Unless correction for heterogeneity of variance is made, animals will tend to be selected from the more variable groups, especially if selection is intense. This is an accurate and fair procedure only when the heterogeneity reflects real differences in heritability. It is shown that, if observations are expressed as deviations relative to the estimate of standard deviation from the group, the accuracy is high unless groups are very small.

The genetic correlation between characters maintained by selection, linkage and inbreeding.

Abstract: Mutation is modelled in two quantitative characters under separate genetic control in a large population. A bivariate pattern of selection acts to correlate the characters and, without pleiotropy, their genetic correlation is due entirely to linkage disequilibrium. Data on spontaneous mutation, the effective number of genes, and the intensity of natural selection on quantitative characters are used to evaluate the models. It is concluded that, even when selection favors a high correlation between the characters, with random mating and no linkage between loci influencing different traits the genetic correlation between characters is likely to be small in magnitude. A genetic correlation of large magnitude can be maintained only if the loci influencing different characters are tightly linked, or there is a high level of inbreeding in the population created by frequent mating between closely related individuals.

Estimating the Effect of Training Programs with Non-Random Selection

Abstract: This study reports on efforts to use the Continuous Longitudinal Manpower Survey to estimate the effect that manpower training programs have had on participants' earnings. Estimation techniques are developed to control for nonrandom selection into the program based on individual unobservables which are either constant and/or changing over time, as well as non-random selection because of "creaming" by program administrators. The study finds that, in general, fixed effects estimators are sufficient to eliminate the bias created by non-random selection. While women appear to benefit substantially from manpower training programs, no significant earnings effects were found for men participants. G OVERNMENTAL involvement in postschooling employment and training programs for disadvantaged and hard to employ workers began with the passage of the Manpower Development and Training Act of 1962. Although funding levels and objectives have changed frequently, training programs of one type or another have been an increasingly significant factor in the operation of the U.S. economy since that time. For almost a decade the Comprehensive Employment and Training Act of 1973 (CETA) had major responsibility for provision of training, serving over four million participants during 1979.1 The purpose of training programs, as defined by CETA, was "to provide training and employment opportunities for economically disadvantaged, unemployed, or underemployed persons which will result in an increase in their earned income."2 Despite nearly a decade of massive expenditures on training under CETA, surprisingly little is known about the program's effectiveness in achieving its goal of human resources development. This study reports on efforts to use the recently available Continuous Longitudinal Manpower Survey (CLMS) to estimate the effect that CETA has had on participants' post-training earnings.3 The plan of the paper is as follows. Section I develops a range of estimation techniques, given alternative assumptions about the structure of the error term. A series of nested hypotheses tests is suggested as a method for choosing which estimation technique(s) fulfills the necessary assumptions for unbiased estimation of training effects. Section II describes the data that are available from the CLMS. The framework developed in section I is then used to test which of four available comparison groups are appropriate for unbiased estimation and presents the empirical results and their limitations. Section III summarizes the findings of

Life history traits and natural selection for small body size in a population of darwin's finches.

Abstract: Application of the theory and methods of quantitative genetics to life history studies has led to a focus on the measurement of phenotypic and genetic covariances between life history traits (Stearns, 1980, 1982a, 1982b; Dingle and Hegmann, 1982 p. 231-244; Etges, 1982; Giesel et al., 1982; Hegmann and Dingle, 1982; Lande, 1982; Rose, 1983). These covariances are the essential parameters in theoretical models describing the evolution of such traits. Estimation of genetic covariance is based on the resemblance between relatives. Genetic covariances have usually been estimated in the laboratory where the environment is controlled and the main cause of mortality is often senescence. Covariances are less easy to estimate in nature because environmental correlations are likel.y to fluctuate greatly in magnitude and sign with changing conditions (Lande, 1982) and because causes of mortality also vary. Thus direct estimates of genetic covariances between life history traits will vary (Giesel et al., 1982; Stearns, 1982a, 1982b). In this paper we adopt an alternative, indirect, approach to estimating covariances between life history traits in natural populations. It depends on the measurement of selectioni on a morphological character at two life history stages, and the assumption that much of the variance in fitness at each stage is due to variance in the character or characters upon which selection acts. Two life history traits, such as probability of survival over two given developmental stages, may be said to covary if they are each determined by the same morphological character or characters. The size and direction of the covariance can be qualitatively estimated from the magnitude and directions of selection. Further, if the morphological character is found to be highly heritable it can be inferred that the two life history traits covary genetically. Boag and Grant (1981) observed intense natural selection favoring large beak and body size in a population of Darwin's Medium Ground finches, Geospiza fortis, associated with adult mortality during a drought. The main cause of mortality was starvation, and differential survival with respect to morphology was at least partly a reflection of differential handling ability of the foods remaining in the environment (Boag and Grant, 1981). Since size measures are highly heritable, with some highly repeatable measures such as beak depth having heritabilities of over .8 (Boag and Grant, 1 978; Boag, 1983), the probability of adult survival with respect to size characters is also expected to be a highly heritable character, provided that adult mortality based on size results from the same general causes in different generations. In this paper we consider the possibility of selection on body size at other stages of the life cycle. Specifically we ask, was the directional selection an isolated event with long term evolutionary consequences, or is it balanced by selection favoring small body size at other stages of the life cycle? To answer this question we examine the possibility of selection on body size associated with juvenile mortality. If selection at this life history stage is found we can follow the reasoning developed above. In particular we can argue that probability ofjuvenile survival is heritable, and genetically negatively covaries with pirobability of adult survival. In doing so, we assume juvenile

The evolutionary implications of mobile genetic elements

Abstract: INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Evolutionary Hypotheses . .. . . . .. . . . .. . . ..... . . . . . . . . . ........ . . . .. . ....... . . .... . ... . .. . . . . General Considerations .. . . .............. . . . ....... ........ . ... . . . . . ...... . ............ . . . . . . ... . BACTERIAL INSERTION SEQUENCES ..................................................... . . Self-Regulation of ISJO and IS50 Movement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Effect of IS Insertion on Gene Expression ............................................ . . Growth Competition Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TRANSPOSONS IN yEAST ...................................................................... .

Stages and levels in human-machine interaction

Abstract: The interaction between a person and a computer system involves four different stages of activities--intention, selection, execution, and evaluation--each of which may occur at different levels of specification. Analysis of these stages and levels provides a useful way of looking at the issues of human-computer interaction.