雌性在受孕期可能与多个雄性交配，因而精子会在体内为争夺进入卵子的机会而展开激烈竞争，这读过《 精子战争 》一书的都知道。许多时候，雌性会故意造成这种竞争局面，以便筛选出在精子战争中表现最佳的精子，这也很容易想到。最近，对果蝇的研究发现，雌性引发精子战争还有另外的作用：通过强化精子竞争来抑制不合作基因的扩散，这些“坏基因”试图通过扭曲配子性别比（我猜大概是通过干扰[[Meiosis|减数分裂]]过程来实现）来提高自己进入子代的机会，但因为这种扭曲常对精子的功能有伤害，它们在精子战争中的表现往往较差。下面摘自 ScienceNOW的有关报道 ： Females take multiple partners, a behavior called polyandry, in many species, including mice. Some researchers have suggested that polyandry evolved to help females boost the likelihood that their offspring will carry certain positive traits such as virility. They can collect sperm through multiple matings, and only the most competitive of this "sperm cocktail" will fertilize their eggs... To test whether females might evolve polyandry in response to the gene, the researchers ran an evolutionary experiment. They compared mating behavior between four fruit fly lines in which the selfish gene was present in about 30% of the males, and eight fruit fly lines lacking the gene entirely. Females in all the fruit fly lines showed nearly identical mating rates at the outset of the experiment. But after 10 generations, females from the selfish gene population remated, on average, almost a full day sooner than females from the populations without the selfish gene, the researchers report today in Science (p. 1241)... 这是 Science上的论文摘要 ： It is unknown why females mate with multiple males when mating is frequently costly and a single copulation often provides enough sperm to fertilize all a female's eggs. One possibility is that remating increases the fitness of offspring, because fertilization success is biased toward the sperm of high-fitness males. We show that female Drosophila pseudoobscura evolved increased remating rates when exposed to the risk of mating with males carrying a deleterious sex ratio–distorting gene that also reduces sperm competitive ability. Because selfish genetic elements that reduce sperm competitive ability are generally associated with low genetic fitness, they may represent a common driver of the evolution of polyandry. 注：这里的selfish gene不是道金斯意义上的自私基因（他认为所有基因都是自私的），而是特指基因组里那些不合作的基因，它们通过损害其它基因的遗传利益来增加自己进入子代的机会。