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  3. The evolution of sex ratio has produced, in most plants and animals with se

The evolution of sex ratio has produced, in most plants and animals with se

游客2024-10-26  29
问题      The evolution of sex ratio has produced, in most plants and animals with separate sexes, approximately equal numbers of males and females. Why should this be so? Two main kinds of answers have been offered. One is couched in terms of advantage to population. It is argued that the sex ratio will evolve so as to maximize the number of meetings between individuals of the opposite sex. This is essentially a "group selection" argument. The other, and in my view correct, type of answer was first put forward by Fisher in 1930. This "genetic" argument starts from the assumption that genes can influence the relative numbers of male and female offspring produced by an individual carrying the genes①. That sex ratio will be favored which maximizes the number of descendants an individual will have and hence the number of gene copies transmitted. Suppose that the population consisted mostly of females, and then an individual who produced sons only would have more grandchildren. In contrast, if the population consisted mostly of males, it would pay to have daughters. If, however, the population consisted of equal numbers of males and females, sons and daughters would be equally valuable. Thus a one-to-one sex ratio is the only stable ratio; it is an "evolutionarily stable strategy". Although Fisher wrote before the mathematical theory of games had been developed, his theory incorporated the essential feature of a game that the best strategy to adopt depends on what others are doing.
     Since Fisher’s time, it has been realized that genes can sometimes influence the chromosome or gamete in which they find themselves so that the gamete will be more likely to participate in fertilization②. If such a gene occurs on a sex-determining (X or Y) chromosome, then highly aberrant sex ratios can occur. But more immediately relevant to game theory are the sex ratios in certain parasitic wasp species that have a large excess of females. In these species, fertilized eggs develop into females and unfertilized eggs into males. A female stores sperm and can determine the sex of each egg she lays by fertilizing it or leaving it unfertilized. By Fisher’s argument, it should still pay a female to produce equal numbers of sons and daughters. Hamilton, noting that the eggs develop within their host—the larva of another insect—and that the newly emerged adult wasps mate immediately and disperse, offered a remarkably cogent analysis. Since only one female usually eggs in a given larva, it would pay her to produce one male only, because this one could fertilize all his sisters on emergence. Like Fisher, Hamilton looked for an evolutionarily stable strategy, but he went a step further in recognizing that he was looking strategy. [br] What can we know about the scientists Fisher and Hamilton from the passage?
选项 A、They both made contribution to the mathematical theory of games.
B、They both sought an explanation of why certain sex ratios exist and remain stable
C、The former stressed the maximization and the latter emphasized the optimization.
D、They both inherited the insight Of the "group selection" argument.
答案 B
解析 事实细节题。考查Fisher和Hamilton的两个论点的共性，选项A 和D 不符合文章意思，选项 C 是干扰项，从第一段第五句话我们知道最大化是集体选择论的观点。实际上Fisher和Hamilton都认同最优化。选项B 正确。Fisher的观点在第一段第九句集中体现，Hamilton此观点与Fisher的相似性在文章最后一句得到体现。
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