Clutton-Brock T H, Iason G R
Q Rev Biol. 1986 Sep;61(3):339-74. doi: 10.1086/415033.
Parents will increase their fitness by varying the sex ratio of their progeny in response to differences in the costs and benefits of producing sons and daughters. Sex differences in energy requirements or viability during early growth, differences in the relative fitness of male and female offspring, and competition or cooperation between siblings or between siblings and parents might all be expected to affect the sex ratio. Although few trends have yet been shown to be consistent, growing numbers of studies have demonstrated significant variation in birth sex ratios in non-human mammals. These are commonly cited as evidence of adaptive manipulation of the sex ratio. However, several different mechanisms may affect the birth sex ratio, and not all of them are likely to be adaptive. Valid evidence that sex ratio trends are adaptive must be based either on the overall distribution of those trends or on cases in which the sex ratio can be shown to vary with the relative fitness of producing sons and daughters. The distribution of observed sex ratio trends does not conform closely to the predictions of any single adaptive theory. Some recent studies, however, indicate that, within species, the sex ratio varies with the costs or benefits of producing male or female offspring.
父母会根据生育儿子和女儿的成本与收益差异来改变后代的性别比例，从而提高自身的适应性。早期生长过程中能量需求或生存能力的性别差异、雄性和雌性后代相对适应性的差异，以及兄弟姐妹之间或兄弟姐妹与父母之间的竞争或合作，都可能影响性别比例。尽管目前很少有趋势被证明是一致的，但越来越多的研究表明，非人类哺乳动物的出生性别比例存在显著差异。这些差异通常被视为性别比例适应性调控的证据。然而，有几种不同的机制可能会影响出生性别比例，而且并非所有机制都可能是适应性的。性别比例趋势具有适应性的有效证据必须基于这些趋势的总体分布，或者基于能够证明性别比例随生育儿子和女儿的相对适应性而变化的案例。观察到的性别比例趋势分布与任何单一适应性理论的预测都不太相符。然而，最近的一些研究表明，在同一物种内，性别比例会随着生育雄性或雌性后代的成本或收益而变化。
