The concept of evolvability—the capacity of a population to produce and maintain evolutionarily relevant variation—has become increasingly prominent in evolutionary biology. Paleontology has a long history of investigating questions of evolvability, but paleontological thinking has tended to neglect recent discussions, because many tools used in the current evolvability literature are challenging to apply to the fossil record. The fundamental difficulty is how to disentangle whether the causes of evolutionary patterns arise from variational properties of traits or lineages rather than being due to selection and ecological success. Despite these obstacles, the fossil record offers unique and growing sources of data that capture evolutionary patterns of sustained duration and significance otherwise inaccessible to evolutionary biologists. Additionally, there exist a variety of strategic possibilities for combining prominent neontological approaches to evolvability with those from paleontology. We illustrate three of these possibilities with quantitative genetics, evolutionary developmental biology, and phylogenetic models of macroevolution. In conclusion, we provide a methodological schema that focuses on the conceptualization, measurement, and testing of hypotheses to motivate and provide guidance for future empirical and theoretical studies of evolvability in the fossil record.

In this paper, I reply to Sharon Street’s objection against quasi-realism, according to which this theory is subject to a problem of unexplained coincidence between the normative truths and our evaluative attitudes. I argue that this problem cannot be applied to quasi-realism because the necessary element for it to be applied is missing in this theory: an ontological commitment towards robust normative entities. This lack of commitment allows quasi-realists to argue for a minimalist conception of normative truths, and to escape the scope of the problem of unexplained coincidence.

This paper contributes to our understanding of why delegitimising focusing events, combined with the mobilisation of policy losers, does not always result in major policy change by undermining a monopolistic policy image and policy subsystem. Based on a close enquiry of American biofuel policy development, it argues that we can make headway in this endeavour by focusing on three factors: first, the congruence of a policy image with core values of the polity; second, the multidimensionality of a policy image; and third, policy image management strategies that maintain cohesion among coalition supporters and respond to outside criticism. In understanding better why some policy images (and policy monopolies) prove resilient when they come under assault, this paper offers a single case plausibility probe supported by indicative evidence from other policy studies.

Artificial-selection experiments constitute an important source of empirical information for breeders, geneticists and evolutionary biologists. Selected characters can generally be shifted far from their initial state, sometimes beyond what is usually considered as typical inter-specific divergence. A careful analysis of the data collected during such experiments may thus reveal the dynamical properties of the genetic architecture that underlies the trait under selection. Here, we propose a statistical framework describing the dynamics of selection-response time series. We highlight how both phenomenological models (which do not make assumptions on the nature of genetic phenomena) and mechanistic models (explaining the temporal trends in terms of e.g. mutations, epistasis or canalization) can be used to understand and interpret artificial-selection data. The practical use of the models and their implementation in a software package are demonstrated through the analysis of a selection experiment on the shape of the wing in Drosophila melanogaster.

The genus Drosophila is diverse and heterogeneous and contains a large number of easy-to-rear species, so it is an attractive subject for comparative studies. The ability to perform such studies is currently compromised by the lack of a comprehensive phylogeny for Drosophila and related genera. The genus Drosophila as currently defined is known to be paraphyletic with respect to several other genera, but considerable uncertainty remains about other aspects of the phylogeny. Here, we estimate a phylogeny for 176 drosophilid (12 genera) and four non-drosophilid species, using gene sequences for up to 13 different genes per species (average: 4333 bp, five genes per species). This is the most extensive set of molecular data on drosophilids yet analysed. Phylogenetic analyses were conducted with maximum-likelihood (ML) and Bayesian approaches. Our analysis confirms that the genus Drosophila is paraphyletic with 100% support in the Bayesian analysis and 90% bootstrap support in the ML analysis. The subgenus Sophophora, which includes Drosophila melanogaster, is the sister clade of all the other subgenera as well as of most species of six other genera. This sister clade contains two large, well-supported subclades. The first subclade contains the Hawaiian Drosophila, the genus Scaptomyza, and the virilis-repleta radiation. The second contains the immigrans-tripunctata radiation as well as the genera Hirtodrosophila (except Hirtodrosophila duncani), Mycodrosophila, Zaprionus and Liodrosophila. We argue that these results support a taxonomic revision of the genus Drosophila.

In this study we estimate the frequency at which P-element insertion events, as identified by in situ hybridization, generate lethal and mild viability mutations. The frequency of lethal mutations generated per insertion event was 0·004. Viability dropped an average of 1% per insertion event. Our results indicate that it is deletions and rearrangements resulting from the mobilization of P elements already in place and not the insertions per se that cause the drastic effects on viability and fitness observed in most studies of P–M dysgenesis-derived mutations. Elements of five other families (I, copia, 412, B104, and gypsy) were not mobilized in these crosses. Finally, we contrast the density of P elements on the X chromosome with the density on the four autosomal arms in a collection of thirty genomes from an African population. The relative number of P elements on the X chromosome is too high to be explained by either a hemizygous selection or a neutrality model. The possible reasons for the failure to detect selection are discussed.

Repeated efforts to estimate the genomic deleterious mutation rate per generation (U) in Drosophila melanogaster have yielded inconsistent estimates ranging from 0·01 to nearly 1. We carried out a mutation-accumulation experiment with a cryopreserved control population in hopes of resolving some of the uncertainties raised by these estimates. Mutation accumulation (MA) was carried out by brother–sister mating of 150 sublines derived from two inbred lines. Fitness was measured under conditions chosen to mimic the ancestral laboratory environment of these genotypes. We monitored the insertions of a transposable element, copia, that proved to accumulate at the unusually high rate of 0·24 per genome per generation in one of our MA lines. Mutational variance in fitness increased at a rate consistent with previous studies, yielding a mutational coefficient of variation greater than 3%. The performance of the cryopreserved control relative to the MA lines was inconsistent, so estimates of mutation rate by the Bateman–Mukai method are suspect. Taken at face value, these data suggest a modest decline in fitness of about 0·3% per generation. The element number of copia was a significant predictor of fitness within generations; on average, insertions caused a 0·76% loss in fitness, although the confidence limits on this estimate are wide.

We studied the dominance of the effects of chromosomes carrying unselected mutations on five life-history traits in Drosophila melanogaster. Mutations were accumulated on the second chromosome for 44 generations in the absence of natural selection. Traits studied were female fecundity early and late in adult life, male mating ability, and male and female longevity. Homozygous effects were estimated for 50 mutant lines, and heterozygous effects were estimated by crossing these lines in a partial diallel scheme. Direct estimates of dominance showed that the effects of mutants are at least partially recessive. Heterozygotes had higher trait means than homozygotes in all five cases, and these differences were significant for late fecundity and female longevity. For all traits, genetic variance was larger among homozygous crosses than among heterozygous crosses. These results are consistent with those of many other studies that suggest that both unselected mutations and those found segregating in natural populations are partially recessive.

Although cryopreservation is routinely used for the storage of a range of biological organisms, few studies have been conducted to determine whether cryopreservation increases the frequency of mutation. A procedure for the cryopreservation of Drosophila melanogaster embryos has recently been developed. Cryopreservation of D. melanogaster is of special interest to geneticists and evolutionary biologists because it would make it possible to assay control and experimental populations simultaneously during long-term studies. Before cryopreserved embryos can be used for such studies, it is first necessary to show that cryopreservation is not mutagenic. We tested for mutagenic effects of cryopreservation in D. melanogaster embryos with an X-linked, recessive lethal assay. The mutation rates of cryopreserved and control flies were not significantly different. We can be 95% certain that cryopreservation does not increase mutation by a factor greater than 2·39. This is the first quantitative estimate of the mutagenic effect of cryopreservation on the germ line of a metazoan. The results are reassuring when considering the genetic impact of cryopreservation on mammalian gametes and embryos.