Perturbation expansions of multilocus fixation probabilities for frequency-dependent selection with applications to the Hill-Robertson effect and to the joint evolution of helping and punishment.

Natural populations are of finite size and organisms carry multilocus genotypes. There are, nevertheless, few results on multilocus models when both random genetic drift and natural selection affect the evolutionary dynamics. In this paper we describe a formalism to calculate systematic perturbation expansions of moments of allelic states around neutrality in populations of constant size. This allows us to evaluate multilocus fixation probabilities (long-term limits of the moments) under arbitrary strength of selection and gene action. We show that such fixation probabilities can be expressed in terms of selection coefficients weighted by mean first passages times of ancestral gene lineages within a single ancestor. These passage times extend the coalescence times that weight selection coefficients in one-locus perturbation formulas for fixation probabilities. We then apply these results to investigate the Hill-Robertson effect and the coevolution of helping and punishment. Finally, we discuss limitations and strengths of the perturbation approach. In particular, it provides accurate approximations for fixation probabilities for weak selection regimes only (Ns < or = 1), but it provides generally good prediction for the direction of selection under frequency-dependent selection.

La consolidació de les especialitats mèdiques a la Catalunya republicana a través d’una revista de resums: La Medicina Catalana. Portantveu de l’Occità nia mèdica (Barcelona, 1933-1938)

Les especialitats mèdiques van tenir un ràpid desenvolupament al món occidental a principis del segle XX. La situació de Catalunya abans de la Guerra Civil, situada als confins de l’Europa d’entreguerres, afavoreix els intents de comunicació científica entre metges catalans i occitans més enllà de les fronteres de grans estats, Espanya i França, amb l’ús d’una llengua pròpia vehicular, el català. Així neix a Barcelona el 1933 la revista La Medicina Catalana, sota la direcció de Leandre Cervera i Astor, constituïda principalment per ressenyes en català d’articles apareguts a revistes internacionals. L’objectiu és estudiar l’aparició i consolidació de les especialitats mèdiques a Catalunya.

Mr John [Llewellyn] Lewis, président du syndicat des mineurs des Etats-Unis : [photographie de presse] / [Agence Rol]

Référence bibliographique : Rol, 56990

Mr Andrew [Muter John] Ogilvie [directeur des transmissions de l'armée anglaise] : [photographie de presse] / [Agence Rol]

Référence bibliographique : Rol, 57288

Les limites de la performativité des énoncés économiques: les apports de John Searle

The problematic of performativity has recently produced several criticisms and debates about the status of the economic discourse. Indeed the affirmation that economist shapes the world by describing it could leads to the subjectivist idea that each theory can in fine be 'true' and each theory can perform the social world in his specific way. This work clarifies this problematic in connecting it with the institutional theory of John Searle. We define performativity as a particular type of assignment of function. Finally, this enables us to show that performativity is limited by two kinds of factors : brut facts and social facts.