Natural habitats are rapidly changing due to climate change and globalization. This can break down mating barriers between species and lead to increased hybridization rates. How detrimental or beneficial hybridization is for population fitness and adaptation is usually unknown and depends on genetic and environmental factors. Here, we use experimental evolution with the model system yeast to investigate at what level of parental divergence the genetic variation gained through hybridization can assist populations with adaptation, across a large range of novel environmental stress. We made F1 and F2 ‘hybrid’ crosses between populations evolving in the laboratory for up to 1000 generations at five timepoints of divergence and compared the fitness of parents and hybrids in 50 stressful environments. In this SNIC project we will examine PoolSeq data of these F1 and F2 hybrids along with the parental populations. In addition, we will analyze a related new experiment on the adaptation to Lithium acetate that expands on previous findings.