The research examined rapid evolution in two populations of the California plant Clarkia xantiana in response to multi-year extreme drought. Both populations experienced similar drought intensity and significant demographic decline, but were estimated to have significant additive genetic variances for flowering phenology. An earlier flowering phenology developed in only one population (S22), both towards the end of the drought and after it ended. In the second population (KYE), evolution did not occur due to a stronger seed bank, which led to lower germination and higher seed survival. This seed bank caused maladaptive gene flow over time, hindering the evolutionary response. The study combined long-term demographic and environmental data, estimates of quantitative genetic components, a seed resuscitation experiment, and evolutionary simulations. The results suggest that gene flow through seed banks can significantly limit rapid evolution under extreme environmental changes.[1][2]