The problem of organismal form played a privileged role throughout the history of biology. However, since the end of the 19th century, the significance of morphology progressively weakened until its practical disappearance in the context of the triumph of the Modern evolutionary synthesis (MS) and the genetic theory of development. However, since the late 1970s, morphology has experienced a renaissance in almost every domain of biology which has brought the spatial dimension of biological entities back to the fore. The return of form in the biosciences has awaken the interest on the history of morphology, and drawn an increasing philosophical attention to the Aristotelian notion of ‘formal causation’ as well as to morphological concepts such as ‘type’, ‘homology’ or ‘novelty’. However, many historical and philosophical challenges related to the morphological approach to development and evolution remain to be explored. My post-doc project at aims at addressing some of these challenges: (1) to explore the historical roots and to analyse the epistemological and ontological implications of the taxonomical and the morphological approach to the problem of form; (2) to examine the interweaving of modelling practices and explanations in developmental biology and evo-devo; (3) to distinguish the conceptions of causality underlying different explanatory strategies of form in developmental biology and evo-devo; (4) to investigate the relationship between form and organisation in developmental and evolutionary biology. In line with my philosophical project, I aim at (5) developing a epigenetic hypothesis on one of the most classic and still unsolved problems in the history of evolutionary theory: the origin of vertebrate limbs. According to our hypothesis, the number and position of the paired appendages along the A-P and D-V axis of vertebrates are due to a commonality of tissue environments determined by the global interactions that relate the two types (somatic and visceral) of lateral plate mesoderm.