EXPLABIO aims at investigating modes of explanations in evolutionary biology, in order to assess current attempts to extend or revise the classical framework (elaborated in 1930-1950) called "Modern Synthesis", that was centered on the crucial explanatory role of population genetics as the science of the process of evolution by natural selection. We assume that recent advances in ecology, molecular biology and evolutionary theory of development ("Evo-Devo") are characterized by novel explanatory structures and features, that call for a new account of the explanatory nature of evolutionary biology. EXPLABIO will elaborate such account. For evolutionary biologists, the space of explanations is structured along two axes, namely the two questions: "How does selection proceed?", and "why is there selection"; then a third axis concerns the mechanistic or topological character of explanations - « topological » meaning here the explanatory character of a set of properties of an abstract structure (like the a phase space, or a fitness landscape) associated to the system under study. EXPLABIO will build this space in details, achieving four interconnected tasks : investigating the explananda of natural selection as population-level explanation; exploring the modes of topological explanation at different levels and their articulation with mechanistic explanation; questioning the status of neutral processes and neutral networks as pervasive explanatory tools in ecology (i.e. Hubbell's "neutral theory of ecology") and evolution (i.e. Kimura's neutralist theory of molecular evolution), and thereby the explanatory status of neutrality and randomness; and finally, addressing the role of time- and space-scale decoupling and coupling in the definition of explananda and the choice of models. For biology, the overall outcome will consist in indications about which complementarities and antagonisms exist between rival theories and their methodologies; for philosophy, we aim at a clearer understanding of what respective roles stochasticity and determinism, population level and individual level, as well as scale separation, play in overall biology. These tasks will be successively tackled, using mathematical tools to define conditions of validity of kinds of explanations, and empirical data (such as data about Gene Regulatory Network of a given cell type in a given species, or about two comparable ecological communities at a same trophic level) to check the fulfillment of these conditions for specific systems. EXPLABIO will be carried on by a team of philosophers of science, evolutionary and molecular biologists and ecologists, including two post-docs hired for the project. It is a truly interdisciplinary project: task 1 is led by a philosopher task 3 and 4 are led by biologists, task 2 is co-led by a biologist and a philosopher. It will be done essentially at the IHPST (CNRS/Université Paris I Sorbonne), an internationally acknowledged center for philosophy of science, which holds long-lasting collaborations with biology institutions and scientists, as well as with other major international centers in philosophy of science such as Cambridge, Toronto, Duke or Montreal. Interdisciplinary workshops will give rise to collected publications, and mathematical and empirical work will be done to formulate hypotheses about the validity of implicit assumptions for specific explanatory strategies (pertaining either to the Modern Synthesis or to an alternative account), and test them. Deliverables will include coauthored papers in scientific journals in philosophy of science and theoretical biology, as well as edited volumes on the results of the tasks.