When beneficial mutations are rare, they accumulate by a series of selective sweeps. But when they are common, many beneficial mutations will occur before any can fix, so there will be many different mutant lineages in the population concurrently. In an asexual population, these different mutant lineages interfere and not all can fix simultaneously. In addition, further beneficial mutations can...

This paper explores the relationship between the two main dimensions of early-life environment, namely disease burden (measured by infant mortality) and economic conditions (measured by income or consumption per capita), and height and body-mass index (BMI) for six annual cohorts of young Italian men born between 1973 and 1978. By combining micro-level data on height and weight with regional- a...

Post-Secondary Education in Canada: Can Ability Bias Explain the Earnings Gap Between College and University Graduates? Using the Canadian General Social Survey we compute returns to post-secondary education relative to high-school. Unlike previous research using Canadian data, our dataset allows us to control for ability selection into higher education. We find strong evidence of positive abil...

Congenic strains can now be constructed guided by the transmission of DNA markers. This allows not only selection for transmission of a desired, donor-derived differential region but also selection against the transmission of unwanted donor origin genomic material. The additional selection capacity should allow congenic strains to be produced in fewer generations than is possible with random ba...

The T cell coreceptors CD4 and CD8 enhance T cell responses to TCR signals by participating in complexes containing TCR, coreceptor, and MHC molecules. These ternary complexes are also hypothesized to play a seminal role during T cell development, although the precise timing, frequency, and consequences of TCR-coreceptor-MHC interactions during positive selection and lineage commitment remain u...

Structurally distinct, self-templating prion "strains" can encode distinct phenotypes and amplify at different rates depending upon the environment. Indeed, prion strain ensembles can evolve in response to environmental challenges, which makes them highly challenging drug targets. It is not understood how the proteostasis network amplifies one prion strain at the expense of another. Here, we de...

Evolutionary forces shape patterns of genetic diversity within populations and contribute to phenotypic variation. In particular, recurrent positive selection has attracted significant interest in both theoretical and empirical studies. However, most existing theoretical models of recurrent positive selection cannot easily incorporate realistic confounding effects such as interference between s...

Abalone sperm lysin is a non-enzymatic protein that creates a hole for sperm passage in the envelope surrounding the egg. Lysin exhibits species-specificity in making the hole and it evolves rapidly by positive selection. Our studies have focused on combining structural, biochemical, and evolutionary data to understand the mechanism of action and evolution of this remarkable protein. Currently,...