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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  23
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] Compared with the work of Hamilton, what dose the author consider Fisher’s work to be?
选项 A、It is inaccurate but popular, compared with Hamilton’s work.
B、It is accurate, but trivial compared with Hamilton’s work.
C、It is admirable, but not as up-to-date as Hamilton’s work.
D、It is valuable, but at a relatively low level.
答案 D
解析 作者态度题。实际上是考查Fisher和Hamilton两个理论的差异，作者认为二者都对，支持他们观点。但是Hamilton的理论更新，上升到了更高的层次：站在策略的高度来考虑问题(参见文章最后一句话)。而Fisher的则在一个较低的层次。
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