Understanding the mechanisms that generate phenotypic variation and their impact on the course of evolution is a central challenge in modern biology. The genetic architecture of development may limit or bias the phenotypic spectrum obtained after random mutation, deemed developmental bias. These phenotypic biases in turn may influence evolutionary trajectories. Despite the recognition of the importance of developmental biases in constraining and pacing evolution, there is no direct empirical evidence for this potential role. Here, I propose to tackle this key question using the ecologically-relevant avoidance to pathogens in the genetically-tractable organism Caenorhabditis elegans. To this aim, I will: (i) quantify and uncover mechanisms of developmental biases in avoidance behaviour; and (2) test the role of developmental biases on the tempo of phenotypic evolution. On the first objective, I will generate a novel panel of random mutant lines containing a transgene for whole-organism neuronal cell-fate identification, determine developmental biases in locomotor and avoidance behaviour, and uncover mechanisms of developmental biases. On the second objective, I will construct hybrid outbred populations with varying developmental biases to test their impact on the tempo of phenotypic evolution in an ecologically relevant scenario using experimental evolution. To achieve this, I will adopt an innovative interdisciplinary approach that combines my expertise in neurodevelopmental and behaviour genetics, quantitative genetics, genome-editing and know-how with the model C. elegans with that of the host lab in experimental evolution, behaviour ecology and host-pathogen interactions. Thus, promoting an active exchange of multidisciplinary expertise between the two parties. EvoBias will elucidate the role of developmental bias during the evolutionary process and its mechanisms in an ecologically-relevant scenario, and it will be a milestone towards my scientific independence