Passage 60

　　Until recently, scientists did not know of a close vertebrate analogue¹ to the extreme form of altruism² abserved in eusocial insects like ants and bees, whereby individuals cooperate, sometimes even sacrificing their own oppor( 5)tunities to survive and reproduce, for the good of others.
　　However, such a vertebrate society may exist among underground colonies of the highly social rodent³ Hydrocephalusgrabber, the naked mole⁴ rat.
　　A naked mole rat colony， like a beehive， wasp's nest，or（10）termite mound，is ruled by its queen，or reproducing female. Other adult female mole rats neither ovulate nor breed. The queen of the largest member of the colony，and she maintains her breeding status through a mixture of behavioral and，presumably，chemical control. Queens have（15）been long-lived in captivity，and when they die or are removed from a colony one sees violent fighting for breeding status among the larger remaining females，leading to a takeover by a new queen.
Eusocial insect societies have rigid⁵ caste systems，each（20）insects's role being defined by its behavior，body shape，and physiology⁶. In naked mole rat societies，on the other hand，differences in behavior are related primarily to reproductive status （reproduction being limited to the queen and a few males），body size，and perhaps age. Smaller nonbreeding（25）members，both male and female，seem to participate primarily in gathering⁷ food，transporting nest material，and tunneling. Larger nonreaders are active in defending the colony and perhaps in removing dirt from the tunnels. Jarvis' work has suggested that differences in growth rates may influence the length of time that an individual performs（30）a task，regardless of its age.
　　Cooperative breeding has evolved many times in vertebrates，but unlike naked mole rats，most cooperatively breeding vertebrates（except the wild dog，Lycaon pictus）（35）are dominated by a pair of breeders rather than by a single breeding female. The division of labor⁸ within social groups is less pronounced among other vertebrates than among naked mole rats， colony size is much smaller， and mating by subordinate females may not be totally suppressed，（40） whereas in naked mole rat colonies subordinate females are not sexually active， and many never breed.

1. Which of the following most accurately⁹ states the main idea of the passage?
　(A) Naked mole rat colonies are the only known examples of cooperatively breeding vertebrate societies.
　(B) Naked mole rat colonies exhibit social organization based on a rigid caste system.
　(C) Behavior in naked mole rat colonies may well be a close vertebrate analogue to behavior in eusocial insect societies.
　(D) The mating habits of naked mole rats differ from those of any other vertebrate species.
　(E) The basis for the division of labor among naked mole rats is the same as that among eusocial insects.

2. The passage suggests that Jarvis’ work has called into question which of the following explanatory variables for naked mole rat behavior?
　(A) Size
　(B) Age
　(C) Reproductive status
　(D) Rate of growth
　(E) Previously¹⁰ exhibited behavior

3. It can be inferred from the passage that the performance of tasks in naked mole rat colonies differs from task performance in eusocial insect societies in which of the following ways?
　(A) In naked mole rat colonies, all tasks ate performed cooperatively.
　(B) In naked mole rat colonies, the performance of tasks is less rigidly¹¹ determined¹² by body shape.
　(C) In naked mole rat colonies, breeding is limited to the largest animals.
　(D) In eusocial insect societies, reproduction is limited to a single female.
　(E) In eusocial insect societies, the distribution of tasks is based on body size.

4. According to the passage, which of the following is a supposition rather than a fact concerning the queen in a naked mole rat colony?
　(A) She is the largest member of the colony.
　(B) She exerts chemical control over the colony.
　(C) She mates with more than one male.
　(D) She attains¹³ her status through aggression¹⁴.
　(E) She is the only breeding female.

5. The passage supports which of the following inferences about breeding among Lycaon pictus?
　(A) The largest female in the social group does not maintain reproductive status by means of behavioral control.
　(B) An individual’s ability to breed is related primarily to its rate of growth.
　(C) Breeding is the only task performed by the breeding female.
　(D) Breeding in the social group is not cooperative.
　(E) Breeding is not dominated by a single pair of dogs