Maynard Smith's first assumption is violated by species in which males contribute to raising offspring. However, in most species, including mammals, males only contribute genes. Maynard Smith's first assumption is correct. Maynard Smith's second assumption is not correct. Under some conditions, descendants produced by sexual reproduction have a higher fitness than descendants produced by asexual reproduction.
Sex is a short-term adaptation to rapid environmental change.
Sex recreates now-favorable multilocus genotypes that were recently eliminated by selection and sexual reproduction is therefore strongly selected for. Evolutionary Arms race Parasites and their hosts are engaged in a constant struggle, with the host evolving defenses and the parasite evolving mechanisms to counter the host's defenses. A parasite might select in favor of a certain multilocus genotype in one generation, and in favor of a different multilocus genotype in another generation. The response to selection is equal to the heritability times the selection differential. At timberline it is pollinated by a variety of insects, but in the tundra it is pollinated almost exclusively by bumblebees.