2015年MBA阅读理解强化练习题12
Flatfish, such as the flounder, are among the few vertebrates that lackapproximate bilateral symmetry (symmetry in which structures to the left and
right of the body’s midline are mirror images). Most striking among the many
asymmetries evident in an adult flatfish is eye placement: before maturity one
eye migrates, so that in an adult flatfish both eyes are on the same side of the
head. While in most species with asymmetries virtually all adults share the same
asymmetry, members of the starry flounder species can be either left-eyed (both
eyes on the left side of head) or right-eyed. In the waters between the United
States and Japan, the starry flounder populations vary from about 50 percent
left-eyed off the United States West Coast, through about 70 percent left-eyed
halfway between the United States and Japan, to nearly 100 percent left-eyed off
the Japanese coast.
Biologists call this kind of gradual variation over a certain geographic
range a “cline” and interpret clines as strong indications that the variation is
adaptive, a response to environmental differences. For the starry flounder this
interpretation implies that a geometric difference (between fish that are mirror
images of one another) is adaptive, that left-eyedness in the Japanese starry
flounder has been selected for, which provokes a perplexing question: what is
the selective advantage in having both eyes on one side rather than on the
other?
The ease with which a fish can reverse the effect of the sidedness of its
eye asymmetry simply by turning around has caused biologists to study internal
anatomy, especially the optic nerves, for the answer. In all flatfish the optic
nerves cross, so that the right optic nerve is joined to the brain’s left side
and vice versa. This crossing introduces an asymmetry, as one optic nerve must
cross above or below the other. G. H. Parker reasoned that if, for example, a
flatfish’s left eye migrated when the right optic nerve was on top, there would
be a twisting of nerves, which might be mechanically disadvantageous. For starry
flounders, then, the left-eyed variety would be selected against, since in a
starry flounder the left optic nerve is uppermost.
The problem with the above explanation is that the Japanese starry flounder
population is almost exclusively left-eyed, and natural selection never promotes
a purely less advantageous variation. As other explanations proved equally
untenable, biologists concluded that there is no important adaptive difference
between left-eyedness and right-eyedness, and that the two characteristics are
genetically associated with some other adaptively significant characteristic.
This situation is one commonly encountered by evolutionary biologists, who must
often decide whether a characteristic is adaptive or selectively neutral. As for
the left-eyed and right-eyed flatfish, their difference, however striking,
appears to be an evolutionary red herring.
1. According to the text, starry flounder differ form most other species of
flatfish in that starry flounder
are not basically bilaterally symmetric.
do not become asymmetric until adulthood.
do not all share the same asymmetry.
have both eyes on the same side of the head.
2. Which of the following best describes the organization of the text as a
whole?
A phenomenon is described and an interpretation presented and
rejected.
A generalization is made and supporting evidence is supplied and
weighed.
A contradiction is noted and a resolution is suggested and then
modified.
A series of observations is presented and explained in terms of the
dominant theory.
3. The text supplies information for answering which of the following
questions?
Why are Japanese starry flounder mostly left-eyed?
Why should the eye-sidedness in starry flounder be considered
selectively neutral?
Why have biologists recently become interested in whether a
characteristic is adaptive or selectively neutral?
How do the eyes in flatfish migrate?
4. Which of the following is most clearly similar to a cline as it is
described in the second paragraph of the text?
A vegetable market in which the various items are grouped according to
place of origin.
A wheat field in which different varieties of wheat are planted to
yield a crop that will bring the maximum profit.
A flower stall in which the various species of flowers are arranged
according to their price.
A housing development in which the length of the front struts
supporting the porch of each house increases as houses are built up the
hill.
5. Which of the following phrases from the text best expresses the author’s
conclusion about the meaning of the difference between left-eyed and right-eyed
flatfish?
“Most striking” (line 3, paragraph 1)
“variation is adaptive” (line 2, paragraph 2)
“mechanically disadvantageous” (line 7, paragraph 3)
“evolutionary red herring” (line 9, paragraph 4)
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