When it comes to sex, the best-interests of males and females are often in conflict. Much attention has focused on the genetics underlying sexual conflict. However, the role that the mitochondrion plays in promoting such conflict has been neglected. Mitochondrial DNA (mtDNA) is maternally inherited, reaching a dead-end in males. Mutations in mtDNA that increase female reproductive success (hence the transmission rate of mtDNA) will be evolutionary favoured, even if these same mutations impair male success. Such mutations may thus fuel sexually antagonistic co-evolution between the mitochondrial and nuclear genomes. Using robust experimentation to explore this idea, this project stands at the cutting-edge in evolutionary biology.