Passage 27
Until recently, scientists did not know of a close verte-
brate 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 under-
ground colonies of the highly social rodent³ Heterocephalus
glaber, the naked mole⁴ rat.
A naked mole rat colony, like a beehive, wasp’s nest, or
(10) termite⁵ mound⁶, 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 captivity⁷, and when they die or are
removed from a colony one sees violent fighting for breed-
ing status among the larger remaining females, leading to a
takeover by a new queen.
Eusocial insect societies have rigid⁸ caste systems, each
(20)insects’s role being defined by its behavior,body shape, and
physiology. 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 pri-
marily in gathering⁹ 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
(30)may influence the length of time that an individual performs
a task, regardless of its age.
Cooperative breeding has evolved many times in verte-
brates, 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 labor¹⁰ 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.
 
160. Which of the following most accurately¹¹ 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. (C)
(E)   The basis for the division of labor among naked mole rats is the same as that among eusocial insects.
 
161. 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 (B)
(E)   Previously¹² exhibited behavior
 
162. 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 rigidly¹³ determined¹⁴ 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. (B)
(E)   In eusocial insect societies, the distribution of tasks is based on body size.
 
163. 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 attains¹⁵ her status through aggression¹⁶. (B)
(E)   She is the only breeding female.
 
164. 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)
(E)   Breeding is not dominated by a single pair of dogs.
 
165. According to the passage, naked mole rat colonies may differ from all other known vertebrate groups in which of the following ways?
(A)   Naked mole rats exhibit an extreme form of altruism.
(B)   Naked mole rats are cooperative breeders.
(C)   Among naked mole rats, many males are permitted to breed with a single dominant¹⁷ female.
(D)  Among naked mole rats, different tasks are performed at different times in an individual’s life. (A)
(E)   Among naked mole rats, fighting results in the selection of a breeding female.
 
166. One function of the third paragraph of the passage is to
(A)   state a conclusion about facts presented in an earlier paragraph
(B)   introduce information that is contradicted by information in the fourth paragraph
(C)   qualify the extent to which two previously mentioned groups might be similar
(D)  show the chain of reasoning that led to the conclusions of a specific study (C)
(E)   demonstrate that, of three explanatory factors offered, two may be of equal significance

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