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abhasjha
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The pronghorn, an antelope-like mammal that
lives on the western plains of North America, is the
continent's fastest land animal, capable of running 90
kilometers per hour and of doing so for several
(5) kilometers. Because no North American predator is
nearly fast enough to chase it down, biologists have
had difficulty explaining why the pronghorn
developed its running prowess. One biologist,
however, has recently claimed that pronghorns run as
(10) fast as they do because of adaptation to predators
known from fossil records to have been extinct for
10,000 years, such as American cheetahs and long –
Legged hyenas, either of which, it is believed, were
fast enough to run down the pronghorn.
(15) Like all explanations that posit what is called a
relict behavior—a behavior that persists though its only
evolutionary impetus comes from long-extinct environmental
conditions—this one is likely to meet with skepticism.
Most biologists distrust explanations positing relict
(20) behaviors, in part because testing these hypotheses is so
difficult due to the extinction of a principal component.
They typically consider such historical explanations
only when a lack of alternatives forces them to do so.
But present-day observations sometimes yield
(25) evidence that supports relict behavior hypotheses.
In the case of the pronghorn, researchers have
identified much supporting evidence, as several
aspects of pronghorn behavior appear to have been
shaped by enemies that no longer exist. For example,
(30) pronghorns—like many other grazing animals—roam
in herds, which allows more eyes to watch for predators
and diminishes the chances of any particular animal
being attacked but can also result in overcrowding
and increased competition for food. But, since
(35) pronghorns have nothing to fear from present-day
carnivores and thus have nothing to gain from herding,
their herding behavior appears to be another adaptation
to extinct threats. Similarly, if speed and endurance
were once essential to survival, researchers would
(40) expect pronghorns to choose mates based on these
athletic abilities, which they do—with female pronghorns,
for example, choosing the victor after male pronghorns
challenge each other in sprints and chases.
Relict behaviors appear to occur in other animals
(45) as well, increasing the general plausibility of such a
theory. For example, one study reports relict behavior
in stickleback fish belonging to populations that have
long been tree of a dangerous predator, the sculpin.
In the study, when presented with sculpin, these
(50) stickleback fish immediately engaged in stereotypical
antisculpin behavior, avoiding its mouth and swirnming
behind to bite it. Another study found that ground
squirrels from populations that have been free from
snakes for 70,000 to 300,000 years still clearly recognize
(55) rattlesnakes, displaying stereotypical antirattlesnake
behavior in the presence of the snake. Such fear,
however, apparently does not persist interminably.
Arctic ground squirrels, free of snakes for about
3 million years, appear to be unable to recognize the
(60) threat of a rattlesnake, exhibiting only disorganized
caution even after being bitten repeatedly.
6. Which one of the following most accurately states the
main point of the passage?
(A) Evidence from present-day animal behaviors,
together with the fossil record, supports the
hypothesis that the pronghorn's ability to far
outrun any predator currently on the North
American continent is an adaptation to
predators long extinct.
(B) Although some biologists believe that certain
animal characteristics, such as the speed of the
pronghorn, are explained by environmental
conditions that have not existed for many years,
recent data concerning arctic ground squirrels
make this hypothesis doubtful.
(C) Research into animal behavior, particularly into
that of the pronghorn, provides strong evidence
that most present-day characteristics of animals
are explained by environmental conditions that
have not existed for many years.
(D) Even in those cases in which an animal species
displays characteristics clearly explained
by long-vanished environmental conditions,
evidence concerning arctic ground squirrels
suggests that those characteristics will
eventually disappear.
(E) Although biologists are suspicious of
hypotheses that are difficult to test, there is
now widespread agreement among biologists
that many types of animal characteristics are
best explained as adaptations to long-extinct
predators.
17. Based on the passage, the term "principal component"
(line 21) most clearly refers to which one of the
following?
(A) behavior that persists even though the conditions
that provided its evolutionary impetus are
extinct
(B) the original organism whose descendants'
behavior is being investigated as relict behavior
(C) the pronghorn's ability to run 90 kilometers per
hour over long distances
(D) the environmental conditions in response to
which relict behaviors are thought to have
developed
(E) an original behavior of an animal of which
certain present-day behaviors are thought to be
modifications
18. The last paragraph most strongly supports which one of
the following statements?
(A) An absence of predators in an animal's
environment can constitute just as much of a
threat to the well-being of that animal as the
presence of predators.
(B) Relict behaviors are found in most wild animals
living today.
(C) If a behavior is an adaptation to environmental
conditions, it may eventually disappear in the
absence of those or similar conditions.
(D) Behavior patterns that originated as a way of
protecting an organism against predators will
persist interminably if they are periodically
reinforced.
(E)Behavior patterns invariably take longer to
develop than they do to disappear.
19. Which one of the following describes a benefit
mentioned in the passage that grazing animals derive
from roaming in herds?
(A) The greater density of animals tends to
intimidate potential predators.
(B) The larger number of adults in a herd makes
protection of the younger animals from
predators much easier.
(C) With many animals searching it is easier for the
herd to find food and water.
(D) The likelihood that any given individual will be
attacked by a predator decreases.
(E) The most defenseless animals can achieve
greater safety by remaining in the center of the
herd.
20. The passage mentions each of the following as support
for the explanation of the pronghorn's speed proposed
by the biologist referred to in line 8 EXCEPT:
(A) fossils of extinct animals believed to have been
able to run down a pronghorn
(B) the absence of carnivores in the pronghorn's
present-day environment
(C) the present-day preference of pronghorns for
athletic mates
(D) the apparent need for a similar explanation to
account for the herding behavior pronghorns
now display
(E) the occurrence of relict behavior in other species
21. The third paragraph of the passage provides the most
support for which one of the following inferences?
(A) Predators do not attack grazing animals mat are
assembled into herds.
(B) Pronghorns tend to graze in herds only when
they sense a threat from predators close by.
(C) If animals do not graze for their food, they do
not roam in herds.
(D) Female pronghorns mate only with the fastest
male pronghorn in the herd.
(E) If pronghorns did not herd, they would not face
significantly greater danger from present-day
carnivores
lives on the western plains of North America, is the
continent's fastest land animal, capable of running 90
kilometers per hour and of doing so for several
(5) kilometers. Because no North American predator is
nearly fast enough to chase it down, biologists have
had difficulty explaining why the pronghorn
developed its running prowess. One biologist,
however, has recently claimed that pronghorns run as
(10) fast as they do because of adaptation to predators
known from fossil records to have been extinct for
10,000 years, such as American cheetahs and long –
Legged hyenas, either of which, it is believed, were
fast enough to run down the pronghorn.
(15) Like all explanations that posit what is called a
relict behavior—a behavior that persists though its only
evolutionary impetus comes from long-extinct environmental
conditions—this one is likely to meet with skepticism.
Most biologists distrust explanations positing relict
(20) behaviors, in part because testing these hypotheses is so
difficult due to the extinction of a principal component.
They typically consider such historical explanations
only when a lack of alternatives forces them to do so.
But present-day observations sometimes yield
(25) evidence that supports relict behavior hypotheses.
In the case of the pronghorn, researchers have
identified much supporting evidence, as several
aspects of pronghorn behavior appear to have been
shaped by enemies that no longer exist. For example,
(30) pronghorns—like many other grazing animals—roam
in herds, which allows more eyes to watch for predators
and diminishes the chances of any particular animal
being attacked but can also result in overcrowding
and increased competition for food. But, since
(35) pronghorns have nothing to fear from present-day
carnivores and thus have nothing to gain from herding,
their herding behavior appears to be another adaptation
to extinct threats. Similarly, if speed and endurance
were once essential to survival, researchers would
(40) expect pronghorns to choose mates based on these
athletic abilities, which they do—with female pronghorns,
for example, choosing the victor after male pronghorns
challenge each other in sprints and chases.
Relict behaviors appear to occur in other animals
(45) as well, increasing the general plausibility of such a
theory. For example, one study reports relict behavior
in stickleback fish belonging to populations that have
long been tree of a dangerous predator, the sculpin.
In the study, when presented with sculpin, these
(50) stickleback fish immediately engaged in stereotypical
antisculpin behavior, avoiding its mouth and swirnming
behind to bite it. Another study found that ground
squirrels from populations that have been free from
snakes for 70,000 to 300,000 years still clearly recognize
(55) rattlesnakes, displaying stereotypical antirattlesnake
behavior in the presence of the snake. Such fear,
however, apparently does not persist interminably.
Arctic ground squirrels, free of snakes for about
3 million years, appear to be unable to recognize the
(60) threat of a rattlesnake, exhibiting only disorganized
caution even after being bitten repeatedly.
6. Which one of the following most accurately states the
main point of the passage?
(A) Evidence from present-day animal behaviors,
together with the fossil record, supports the
hypothesis that the pronghorn's ability to far
outrun any predator currently on the North
American continent is an adaptation to
predators long extinct.
(B) Although some biologists believe that certain
animal characteristics, such as the speed of the
pronghorn, are explained by environmental
conditions that have not existed for many years,
recent data concerning arctic ground squirrels
make this hypothesis doubtful.
(C) Research into animal behavior, particularly into
that of the pronghorn, provides strong evidence
that most present-day characteristics of animals
are explained by environmental conditions that
have not existed for many years.
(D) Even in those cases in which an animal species
displays characteristics clearly explained
by long-vanished environmental conditions,
evidence concerning arctic ground squirrels
suggests that those characteristics will
eventually disappear.
(E) Although biologists are suspicious of
hypotheses that are difficult to test, there is
now widespread agreement among biologists
that many types of animal characteristics are
best explained as adaptations to long-extinct
predators.
17. Based on the passage, the term "principal component"
(line 21) most clearly refers to which one of the
following?
(A) behavior that persists even though the conditions
that provided its evolutionary impetus are
extinct
(B) the original organism whose descendants'
behavior is being investigated as relict behavior
(C) the pronghorn's ability to run 90 kilometers per
hour over long distances
(D) the environmental conditions in response to
which relict behaviors are thought to have
developed
(E) an original behavior of an animal of which
certain present-day behaviors are thought to be
modifications
18. The last paragraph most strongly supports which one of
the following statements?
(A) An absence of predators in an animal's
environment can constitute just as much of a
threat to the well-being of that animal as the
presence of predators.
(B) Relict behaviors are found in most wild animals
living today.
(C) If a behavior is an adaptation to environmental
conditions, it may eventually disappear in the
absence of those or similar conditions.
(D) Behavior patterns that originated as a way of
protecting an organism against predators will
persist interminably if they are periodically
reinforced.
(E)Behavior patterns invariably take longer to
develop than they do to disappear.
19. Which one of the following describes a benefit
mentioned in the passage that grazing animals derive
from roaming in herds?
(A) The greater density of animals tends to
intimidate potential predators.
(B) The larger number of adults in a herd makes
protection of the younger animals from
predators much easier.
(C) With many animals searching it is easier for the
herd to find food and water.
(D) The likelihood that any given individual will be
attacked by a predator decreases.
(E) The most defenseless animals can achieve
greater safety by remaining in the center of the
herd.
20. The passage mentions each of the following as support
for the explanation of the pronghorn's speed proposed
by the biologist referred to in line 8 EXCEPT:
(A) fossils of extinct animals believed to have been
able to run down a pronghorn
(B) the absence of carnivores in the pronghorn's
present-day environment
(C) the present-day preference of pronghorns for
athletic mates
(D) the apparent need for a similar explanation to
account for the herding behavior pronghorns
now display
(E) the occurrence of relict behavior in other species
21. The third paragraph of the passage provides the most
support for which one of the following inferences?
(A) Predators do not attack grazing animals mat are
assembled into herds.
(B) Pronghorns tend to graze in herds only when
they sense a threat from predators close by.
(C) If animals do not graze for their food, they do
not roam in herds.
(D) Female pronghorns mate only with the fastest
male pronghorn in the herd.
(E) If pronghorns did not herd, they would not face
significantly greater danger from present-day
carnivores
