Sexual reproduction is common in nature, but some theories suggest that asexual organisms may accumulate harmful mutations over time, leading to their decline. However, a study on fish hybrids found no evidence of this. Mutations did increase in the asexual genomes, but they did not become more harmful or affect the fitness of the hybrids. Even the oldest hybrid studied did not show signs of mutation-related fitness decline. This suggests that factors other than mutation accumulation may explain the advantages of sexual reproduction.