Divergence in replicated phylogenies: the evolution of partial post-mating prezygotic isolation in bean weevils

By tradition, speciation research has been focused on processes leading to either premating or post-zygotic reproductive isolation. The processes which generate isolation after mating but before zygote formation are less well understood. Here, we study divergence in characters which contribute to post-mating prezygotic isolation, such as egg production and remating rate. We propose that 'replicated' laboratory phylogenies with known histories can be used to yield insights into the processes of divergence. We performed a series of cross-matings between populations within two strains of the bean weevil Callosobruchus maculatus. Each strain has a unique and independent origin and both have been kept in the same set of laboratories during the last few decades. Our results show that divergence has occurred between laboratory populations within strains with regards to the effects that mating has on female reproductive behaviour, showing that the evolution of partial post-mating prezygotic isolation can be rapid. More importantly, the pattern of divergence across populations was distinct in the two strains, suggesting that coevolutionary trajectories are not determined by environmental factors but are to some extent arbitrary. We discuss the limitations of the novel empirical strategy employed here, and conclude that our results lend support to the hypothesis that post-mating sexual selection is capable of rapidly generating post-mating prezygotic isolation.     

How arbitrary is language?

It is a long established convention that the relationship between sounds and meanings of words is essentially arbitrary—typically the sound of a word gives no hint of its meaning. However, there are numerous reported instances of systematic sound–meaning mappings in language, and this systematicity has been claimed to be important for early language development. In a large-scale corpus analysis of English, we show that sound–meaning mappings are more systematic than would be expected by chance. Furthermore, this systematicity is more pronounced for words involved in the early stages of language acquisition and reduces in later vocabulary development. We propose that the vocabulary is structured to enable systematicity in early language learning to promote language acquisition, while also incorporating arbitrariness for later language in order to facilitate communicative expressivity and efficiency.     

Objectivity and Illusion in Evolutionary Ethics: Comments on Waller

In this paper I argue that any adequate evolutionary ethical theory needs to account for moral belief as well as for dispositions to behave altruistically. It also needs to be clear whether it is offering us an account of the motivating reasons behind human behaviour or whether it is giving justifying reasons for a particular set of behaviours or, if both, to distinguish them clearly. I also argue that, unless there are some objective moral truths, the evolutionary ethicist cannot offer justifying reasons for a set of behaviours. I use these points to refute Waller's claims that the illusion of objectivity plays a dispensable role in Ruse's theory, that my critique of Ruse's Darwinian metaethics is built on a false dilemma, that there is nothing to be distressed about if morality is not objective, and that ethical beliefs are subject to a kind of causal explanation that undermines their objectivity in a way that scientific beliefs are not.