RaviChandra
Until recently, scientists did not know of a close vertebrate analogue to the extreme form of altruism observed in eusocial insects like ants and bees, whereby individuals cooperate, sometimes even sacrificing their own opportunities to survive and reproduce, for the good of others. However, such a vertebrate society may exist among underground colonies of the highly social rodent Heterocephalus glaber, the naked mole rat.
A naked mole rat colony, like a beehive, wasp's nest, or termite mound, is ruled by its queen, or reproducing female. Other adult female mole rats neither ovulate nor breed. The queen is the largest member of the colony, and she maintains her breeding status through a mixture of behavioral and, presumably, chemical control. Queens have 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 rigid caste systems, each insect'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 non-breeding members, both male and female, seem to participate primarily in gathering food, transporting nest material, and tunneling. Larger nonbreeders 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 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) are dominated by a pair of breeders rather than by a single breeding female. The division of labor 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, whereas in naked mole rat colonies subordinate females are not sexually active, and many never breed.
Hi
avigutman GMATNinja IanStewartThis is an interesting passage, but I have some questions that no previous post in this thread has discussed yet, so I decided to write my post and hope you could share some thoughts when you have time.
(By the way, this passage made me curious what these special rats are, and it is really hard to tell from these rats' appearance that they are altruistic--they look special and even a bit aggressive.)
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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 are performed cooperatively.
(B) In naked mole rat colonies, the performance of tasks is less rigidly determined 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.
This is an inference question mainly relevant to the second and third paragraph, which talk about the similarities and difference between the eusocial insects and the naked mole rats. I would like to check all the five options, but first I hope to compare the option (B) and (E).
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(B) In naked mole rat colonies, the performance of tasks is less rigidly determined by body shape.
(E) In eusocial insect societies, the distribution of tasks is based on body size.
I can see why the option (E) is incorrect. Although the paragraph does not explicitly say that the eusocial insects distribute their jobs by the body size, it says that each insect's role is defined by the body shape and it could be inferred that an individual's role in the community is related to the job it does. Because body shape also affects job distribution among rats--larger rats do some jobs and smaller rats do other jobs--the option (E) is gone.
But I am not sure about the option (B), which is the correct answer: "In naked mole rat colonies, the performance of tasks is less rigidly determined by body shape."
Some members said that this could be inferred from "
each insect'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." But I am not fully convinced for two reasons:
1. Does the adverb "primarily" modify only the first noun "reproductive status?" Or, does it modify all the three following nouns?
If it modifies all the three nouns, then body size also plays a primary role in the difference in behavior among rats. I do not think that it is strange for the author to use the adverb "primarily" to modify three nouns at the same time, because he or she might want to express the idea that these three factors are the most primary factors among all factors.
2. The third paragraph talks much about how larger rats do some jobs and smaller rats do other jobs. It seems to me that these descriptions suggest that a rat's body shape affects what kind of jobs it does. Cannot we infer from this information that the body shape plays an important role in the distribution of task in the rat societies?
In eusocial insect societies, each insect's role is defined by three factors including the body shape. And in the rate societies, the body shape also plays an important role. I cannot understand how we can infer that "
In naked mole rat colonies, the performance of tasks is less rigidly determined by body shape."
Meanwhile, I noticed that in the third paragraph, there is an idiom "
on the other hand," which usually suggests whatever comes is to say something different from the preceding message. I tried to use this idiom to help myself understand the difference between the eusocial insects and rats, but to no avail. To be very frank, I am even a bit confused why the author uses this idiom, because the part following "on the other hand" does not really seem very different from the preceding part.
Eusocial insect societies have rigid caste systems, each insect'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.The first part talks about the insects' role, and behavior is one of the three factors deciding the role. The second part, following "on the other hand," talks about the difference in rats' behavior. I think they are more like two separate topics. It would make more sense to me if the author wrote "each insect's role is defined by three factors, and on the other hand, each rat's role is decided by other factors." I am not saying that the "parallelism"/"comparison" concept in the SC section should be applied here, but it just puzzled me whether the idiom "on the other hand" gives us some valuable hints.
I would also like to check the option (C) and (D):
Quote:
(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.
I think these two options are relevant to the second paragraph (cited below). May I confirm whether we can eliminate the option (D) with the sentence that is colored in orange? And, does the description of
the queen, colored in blue, apply only to the rat queen or to both queens of the rat societies and the eusocial insects societies?
A naked mole rat colony, like a beehive, wasp's nest, or termite mound, is ruled by its queen, or reproducing female. Other adult female mole rats neither ovulate nor breed.
The queen is the largest member of the colony, and she maintains her breeding status through a mixture of behavioral and, presumably, chemical control. Queens have 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.At my first read, I thought that the queen only refers to the rat queen. But for my second read, I noticed that the parts describing the queen do not really limit themselves to the scope of the rat societies. Since this paragraph mainly talks about the similarities between the eusocial insects and the rats, I wonder whether these descriptions also apply to the insect queen. This paragraph might be less meaningful if the properties (being the largest member, fighting among other adult female when the queen dies, and so on) are only those of the rat queen, but would still work.
I might be doing more analyses than necessary here, because whether the queen descriptions refers to only the rat queen, we can eliminate the option (C), just for different reasons. But I hope to know how you would understand the queen part in the second paragraph--I feel that I might be able to improve my grasp on reading structure with this.
For the last option (A):
Quote:
(A) In naked mole rat colonies, all tasks are performed cooperatively.
I hope to confirm whether the use of "all" is the main reason the option (A) is gone. From the second and third paragraphs, we can know that both the eusocial insects and the rats perform the tasks cooperatively, but we just do not know the comparative extent of their cooperation, do we?
Sorry that my question is a bit long.
Thank you for your thoughts and insights.