The mutational load of an asexual population is 1-exp(U) , where U is the total deleterious mutation rate per generation. In a sexual population, the load may be substantially less than 1-exp(U) , provided that there are synergistic fitness interactions between mutations. As a result, synergistic interactions would make it possible for sexual species to survive a mutation rate of greater than one. Recent measurements of fitness interactions in the bacteria E. coli and the filamentous fungus A. niger found no synergism on average. I show that synergism is likely to evolve in response to a high mutation rate, but only if species are sexual. I argue that significant synergism may be restricted to obligately sexual species with a high mutation rate.