Software evolution is an important and expensive consequence of software. As Lehman's First Law of Program Evolution states, software must be changed to satisfy new user requirements or become progressively less useful to the stakeholders of the software. Software evolution is difficult for a multitude of different reasons, most notably because of an inherent lack of evolveability of software, design decisions and existing requirements which are difficult to change and conflicts between new requirements and existing assumptions and requirements. Software engineering has traditionally focussed on improvements in software development techniques, with little conscious regard for their effects on software evolution. The thesis emphasises design for change, a philosophy that stems from ideas in preventive maintenance and places the ease of software evolution more at the centre of the design of software systems than it is at present. The approach involves exploring issues of evolveability, such as adaptability, flexibility and extensibility with respect to existing software languages, models and architectures. A software model, SEvEn, is proposed which improves on the evolveability of these existing software models by improving on their adaptability, flexibility and extensibility, and provides a way to determine the ripple effects of changes by providing a reflective model of a software system. The main conclusion is that, whilst software evolveability can be improved, complete adaptability, flexibility and extensibility of a software system is not possible, hi addition, ripple effects can't be completely eradicated because assumptions will always persist in a software system and new requirements may conflict with existing requirements. However, the proposed reflective model of software (which consists of a set of software entities, or abstractions, with the characteristic of increased evolveability) provides trace-ability of ripple effects because it explicitly models the dependencies that exist between software entities, determines how software entities can change, ascertains the adaptability of software entities to changes in other software entities on which they depend and determines how changes to software entities affect those software entities that depend on them.

This thesis examines variation in the life-history parameters of primates using comparative techniques. Several theories of life-history evolution are introduced in the first chapter, together with a summary of the previous work on this topic. Scaling methods are used to separate variation in life-history parameters that is correlated with body weight from that which cannot be predicted from an animal's size. These methods are described in detail in Chapter 2. Chapter 3 describes the variation found in body size and basal metabolic rate and correlations with phylogeny, diet, habitat and other aspects of ecology. Patterns of variation in reproductive parameters, particularly reproductive rates (as measured by the intrinsic rate of natural increase, r_{max}) and reproductive effort (as measured by prenatal and postnatal infant growth rates), are described and compared with patterns reported in other studies. Possible reasons for the scaling relationships found are suggested and the influences of metabolic rate, phylogeny, diet, habitat and other aspects of ecology are investigated. This is carried out for all primates in Chapters 4-6 and in Chapter 7 there is a closer look at the cercopithecine monkeys. It is suggested that r_{max} is influenced by the predictability of the environment, with more unpredictable environments being associated with a higher r_{max} that more predictable environments. However, this is only found when body weight effects are removed from the r_{max} data. Growth rates do not appear to be correlated with environmental predictability but are mainly correlated with body size and relative metabolic rate. There is some indication that the degree of parental care may also be correlated with relative growth rates. It is concluded that no single theory of life-history evolution can amount for the variation found in primate life-histories, but that some aspects of several theories may be useful in describing the patterns found.

No description available.

Our aim in this thesis is to use the clustering of QSOs to investigate large- scale structure and cosmology. We are particularly concerned with estimating the cosmological parameters which govern the evolution of structure in the Universe. We first investigate how QSOs trace the distribution of 'normal' galaxies by measuring the correlation between a sample of ~ 150 QSOs and faint, b(_j) < 23 galaxies. At z < 1.5 we find that the cross-correlation amplitude is marginally negative. This low signal clearly rules out models in which QSOs inhabit rich environments. The environments of QSOs are more similar to those of average galaxies. The slight negative correlation can be explained by gravitational lensing, but this has no effect on our conclusions concerning QSO environments. We determine the clustering properties of a combined sample of > 1500 QSOs including the LBQS and Durham/AAT QSO surveys. This data set has a clustering amplitude Ɛ(10 h(^-1) Mpc) = 0.83 ± 0.29 for Ωₒ = 1 at z = 1.27. On ~ 100 – 1000 h(^-1) Mpc scales the limit on detected signals in Ɛ is ±0.025. A model of clustering evolution which includes the effect of bias was used to compare QSO clustering to the clustering of low redshift galaxies and Seyfert galaxies. If Seyferts and QSOs are similarly clustered, then the data prefer a low Ωₒ or high bias for QSOs and galaxies. In contrast, comparisons to the CMB measurements of COBE assuming a CDM-type power spectrum suggest low bias. This might be taken as evidence for low do, but the data is still consistent with Ωₒ = 1 and b(_gp) ~ b(gp) ~ 2..We consider the possibility that nearby galaxy clusters can gravitationally lense background QSOs. We apply the lensing hypothesis to the result of Boyle et al., (1988) and find that cluster masses required are too large. A small dust component could retrieve the lensing model and allow more reasonable mass estimates for clusters from this method. The requirement for a new, deep, wide-field, QSO survey is clear. We discuss the construction of the candidate catalogue for the 2dF QSO Redshift Survey, which will contain ~ 25000 QSOs. We calibrate the photographic plates used for the candidate catalogue and assess the sources of errors and incompleteness. From preliminary spectroscopic observations we conclude that the completeness of the 2dF catalogue is ~ 71.1 ± 7.1%, compared with an estimated completeness of ~ 80%. We propose to substantially increase the catalogue completeness (to ~ 90%), by the introduction of UKST r plates into our candidate catalogue.

This study aims to understand the key role played by molecular hydrogen in the evolution of galaxies, with a view to constraining its radial distribution in the Galaxy and the CO→H(_2) conversion factor α(_20).The star formation rate is shown to be correlated with the surface density of H(_2). A correlation between the molecular hydrogen fraction and the metallicity of a region allows the time evolution of H(_2) to be described. This leads to a modified 'Schmidt Law' of the SFR which explains quite naturally the production of galactic metallicity gradients and the constancy of the SFR in the absence of infall. A consistent closed model of the chemical evolution of the Galaxy is proposed to solve the G-dwarf problem, the stellar age-metallicity relation and the metallicity gradient, leading to the prediction of some initial amount of pre-disc processing of gas into visible and dark matter. It is found that a constant yield of metals is more appropriate than a yield proportional to metallicity. Possible time variations of the returned fraction, the dark matter fraction and the SFR are also studied. For consistency, we suggest that dark matter in the solar neighbourhood could be totally baryonic provided the Miller-Scalo IMF is modified at the lower end, that is, the dark matter resides in low mass stars or brown dwarfs. The production of metallicity gradients in spiral galaxies is shown to be a direct consequence of the radial variation of the total surface density of matter and the age of the disc. The role of molecular gas in the evolution of the Oort Cloud of comets is examined. It is shown that comet showers with a mean interval of ̴̱ 30My cannot be produced using perturbations of the Oort Cloud by known stars or molecular clouds. If there is indeed an apparent 30My periodicity in the terrestrial mass extinction and geological records, we argue that astronomically induced processes are unlikely to be the primary cause. Evidence is presented that the lifetime of the molecular gas phase is ≤ 2.lO(_8)y, and arguments, particularly from CO observations of the Virgo galaxy cluster, favouring longer lifetimes are shown to be not well founded. We suggest that the ICM in Virgo reduces the value of α(_20) as compared to isolated galaxies. From the above considerations, the radial distribution of in the Galaxy is derived and shown to agree in the inner Galaxy with that derived from ɤ-ray analysis. In the solar neighbourhood we find α(_20) = 2.5±0.5, and present evidence that α(_20) varies as a function of Galactocentric radius and from galaxy to galaxy.

No description available.

The endemic New Zealand frog, Leiopelma hochstetteri, is characterized by variable numbers of mitotically-stable B chromosomes. In order to assess whether the B chromosomes had been derived from the autosome complement, B DNA was isolated and amplified by micromanipulation in conjunction with degenerate oligonucleotide-primed PCR. Southern hybridization patterns of B DNA probes to genomic DNA from males and females characterized by differing numbers of B's demonstrated that the B chromosomes were derived from the univalent W chromosome which is specific to females. The presence of homologous B specific sequences in B chromosomes from geographically-distinct populations show that only a single univalent W to B event had occurred. Furthermore, a plesiomorphic homology shows that the B chromosomes originated soon after the univalent W had been derived from the ancestral WZ/ZZ karyotype, which is still present in frogs from Great Barrier Island. Finally, sequence analysis of the probes reveals that B DNA is composed of repeat sequences, and has the ability to form stable hairpin structures in vivo. The molecular dynamics of these structures may reflect the inherent propensity to undergo rapid change in nucleotide sequence and chromosome structure.

Genomic evolution is a continuous process that involves the accumulation of neutral and adaptive variation within DNA sequences. Duplication, a mechanism that introduces new genetic material into a genome, is thought to be the primary source of new genes that have arisen during vertebrate evolution. This hypothesis, popularized by Susumu Ohno in 1970, has transformed the field of evolutionary biology. Consequently, many evolutionary studies have concentrated on identifying examples of gene duplication and assessing their impact on the evolution of genomes. This thesis presents the identification and analysis of three examples of gene duplication involved in shaping mammalian genomes. Through these analyses, I investigate the fate of duplicated genes and discuss the potential impact of duplication on genomic evolution. The fates depicted within these studies range from the pseudogenization of recent gene duplications to the preservation of ancient duplications for over 100 million years in multiple mammalian genomes. The consequences of these fates include neofunctionalization, subfunctionalization, and gene relocation. In additional, the analyses in this thesis demonstrate different rates and directions of evolution following gene duplication. Some duplicated genes are shown to diverge gradually over time throughout mammalian evolution, while others exhibit an accelerated evolutionary rate within a specific lineage. In other rare cases, divergence is impeded such that duplicated genes evolve in synchronization, under a process known as concerted evolution. This can lead to examples showing mosaic evolution, where both divergent and concerted evolutionary signatures are observed within a single duplicated gene. Through the analyses presented in this thesis, I illustrate some of the different evolutionary histories that result from gene duplication and examine the variety of forces that influence the evolution of duplicated genes. These studies examine the role of duplication in mammalian evolution and represent a significant contribution to the growing body of knowledge in the field of evolutionary biology.

Evolution by natural selection began as a biological concept, but since Darwin it has been recognized to have broader application than biology. Applying evolutionary ideas beyond biology requires that the principles of evolution by natural selection be abstracted and generalized from the biological case. The received view of evolution by natural selection in biology is itself seriously flawed, which understandably renders the project of abstracting it and applying it elsewhere challenging. This thesis develops a generalized account of models of evolution by natural selection which is used to resolve various outstanding issues in the philosophy of biology. This also clarifies the methods and prospects of applying evolution by natural selection to non-biological domains. It does so by analyzing models of evolution both within biology and outside it, relying in particular on the contrast provided by models of firm competition in evolutionary economics. This analysis highlights those aspects of the classical view which must be abandoned or revised, and leads to the development of a neo-dynamical model of evolution, which is developed, explained, defended, and applied to problems in evolutionary biology and multi-level selection theory.

Differential gene expression between sexes is the main contributor of the morphological and behavioral differences observed between them. Studying the signatures of these differences at the genetic level will help us understand the forces acting on them. The existence of androdioecious and gonochoristic species in the genus Caenorhabditis makes it suitable for sex-biased gene expression studies. In this thesis, I have assembled the transcriptome of C. sp. 9 and C. sp. 5 using de novo and reference-based techniques. Evolutionary analysis of the assembled contigs showed that genes with male-biased expression evolve faster than those with a female bias, as observed in other taxa. Furthermore, I found a positive correlation between gene expression and codon usage bias.