The writings of George Williams challenged biologists to think critically about levels of selection, social behavior, and the paradox of sex, whose maintenance by recombination alone has not been convincingly demonstrated in theory or in fact. A solution is suggested by observations of the dependence of females on interaction with males, as a result of sexual selection. This, along with recombination in changing environments and DNA repair during meiosis, may contribute to a pluralistic explanation for the maintenance of sex.