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

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

游客2024-04-28  31
问题     The evolution of sex ratios has produced, in most plants and animals with separate sexes, approximately equal number of males and females. Why should this be so? Two main kinds of answers have been offered. One is【C1】______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【C2】______sex. The other type of answer was first put forward by Fisher in 1930. The "genetic" argument starts from the【C3】______that genes can influence the relative numbers of male and female【C4】______produced by an individual carrying the genes. Suppose that the population consisted mostly of females, it would pay to have sons. In contrast, if the population consisted mostly of males, it would have daughters. If, however, the population consisted of【C5】______numbers of males and females, sons and daughters would be equally valuable. Thus a one-to-one sex ratio is the only【C6】______ratio; it is an "evolutionarily stable strategy". Although Fisher wrote this, before the mathematical theory of games had been developed, his theory【C7】______the essential feature of a game—that the best strategy to adopt depends on what others are doing.
    More immediately relevant to game theory are the sex ratios in certain parasitic wasp(寄生蜂)species that have a large excess of females. In these species, fertilized eggs develop into females and unfertilized eggs into males. A female 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【C8】______to produce equal numbers of sons and daughters. Hamilton, noting that the eggs develop within their host and that the newly emerged adult wasps mate immediately and【C9】______. offered a remarkably reasonable analysis. Like Fisher, Hamilton looked for an【C10】______stable strategy, but he went a step further in recognizing that he was looking for a strategy.
A)female I)predecessor
B)updated J)offspring
C)stable K)disperse
D)incorporates L)couched
E)invariably M)male
F)evolutionarily N)opposite
G)assumption O)homogeneous
H)equal [br] 【C5】
选项
答案 H
解析 此处应填一形容词说明numbers。前两句分别假设当females或males占多数时会出现的情况。而此句后半部分的sons and daughters would be equally valuable，根据前两句内容可以推断出此句假设情况是males和females的数量相同，选H)equal。
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