Sexual selection is a potent evolutionary force that can enhance adaptation and reduce mutational load, while simultaneously reducing survival, or cause sexual conflict that reduces fitness for one or both sexes. Many populations today face not only gradual environmental changes but also extreme, short-term stress events. The combined effects of sexual and environmental selection on population demography during and after such events remain poorly understood, even though such combined effects could be crucial for the persistence of small, endangered populations under climate change. This dataset derives from a multi-generational experimental evolution study investigating how sexual selection interacts with thermal stress to shape population demography in the male-dimorphic soil mite Sancassania berlesei. It includes detailed generational records from 42 populations subjected to a factorial design manipulating sexual selection intensity (via pheromone-induced morph suppression) and exposure to recurrent heatwaves. Key variables include juvenile counts, adult survival before and after heat stress, sex ratios, male morph frequencies (fighter vs. scrambler), and extinction events, recorded over eight generations.The dataset enables fine-scale analysis of how sexually selected traits and environmental stressors jointly affect survival, sex-specific mortality, and extinction risk. It has strong reuse potential for researchers studying eco-evolutionary dynamics, sexual selection, inbreeding, and climate resilience in small populations. All data were collected under standardized laboratory conditions, with no human or vertebrate subjects involved.