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# The evolution of sex ratios has produced, in most plants and

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Joined: 31 Jan 2010
Posts: 488
WE 1: 4 years Tech
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Kudos [?]: 149 [1] , given: 149

The evolution of sex ratios has produced, in most plants and [#permalink]

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28 Dec 2010, 05:19
1
KUDOS
The evolution of sex ratios 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 genes. 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: 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 incorporates 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 fertilization. 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 lays eggs in a given larva, it would pay her to produce one male only, because this one male 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 for a strategy.
21.The author suggests that the work of Fisher and Hamilton was similar in that both scientists
(A) conducted their research at approximately the same time
(B) sought to manipulate the sex ratios of some of the animals they studied
(C) sought an explanation of why certain sex ratios exist and remain stable
(D) studied game theory, thereby providing important groundwork for the later development of strategy theory
(E) studied reproduction in the same animal species
[Reveal] Spoiler:
C

It can be inferred from the passage that the mathematical theory of games has been
(A) developed by scientists with an interest in genetics
(B) adopted by Hamilton in his research
(C) helpful in explaining how genes can sometimes influence gametes
(D) based on animals studies conducted prior to 1930
(E) useful in explaining some biological phenomena

[Reveal] Spoiler:
E

Its given that Fishers theory was based on something that later became a vital part of Mathematical Game theory but its nowhere mentioned that the Mathematical Game Theory has been useful in explaining some biological phenomenon.
What do u mean by "has been useful " ?
BTW i still dont understand the main point of the passage .
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My Post Invites Discussions not answers
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29 Dec 2010, 13:04
I would have chosen E, but that was mainly through elimination...

A - passage doesn't mention who developed game theory
B - possible, but is really a step too far (the passage says Hamiliton was looking for a strategy to explain the stable sex ratio, but doesn't suggest he was relying on game theory)
C - I think the whole genes / gametes thing is a bit of red herring; those two sentences are there to support Fisher's theory but don't go into how the process might work or that the process itself is governed by game theory. If anything, the second sentence suggests that the affect would be random and not strategic: "highly aberrant sex ratios can occur"
D - that would be a bit of a leap, and the last sentence of the first paragraph suggests otherwise (the findings fit with game theory, rather than game theory fitting with the findings)
E - at first glance this does seem a bit backward; Fisher conducted his experiment before game theory was created. However, re-reading the passage, it does become a bit clearer that the author is suggesting that these results fit with what game theory would have predicted, and inferring that game theory could have been used to explain these phenomenon

The first time I read the passage I didn't really like any of the inferences, but then reading it for a second time 'E' stood out as the best choice. I agree that the phrase "has been used" is a bit strong and should probably have been written as "could be used" but then I suppose that might make the correct answer a bit obvious.

For what it's worth, my view is that the passage isn't about sex ratios, but rather the real-world applications of game theory. If you start think about the passage like that then it becomes a bit easier to see what the author is trying to achieve and the inferences they are trying to draw.
Re: 1000 RC SEX   [#permalink] 29 Dec 2010, 13:04
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