Critical Reasoning

Two types of earthworm, one black and one red-brown, inhabit the woods near the town of Millerton. Because the red-brown worm's coloring affords it better camouflage from predatory birds, its population in 1980 was approximately five times that of the black worm. In 1990, a factory was built in Millerton and emissions from the factory blackened much of the woods. The population of black earthworms is now almost equal to that of the red-brown earthworm, a result, say local ecologists, solely stemming from the blackening of the woods.

Which of the following, if true, would most strengthen the conclusion of the local ecologists?

A]The number of red-brown earthworms in the Millerton woods has steadily dropped since the factory began operations.
B]The birds that prey on earthworms prefer black worms to red-brown worms.
C]Climate conditions since 1990 have been more favorable to the survival of the red-brown worm than to the black worm.
D] The average life span of the earthworms has remained the same since the factory began operations.
E]Since the factory took steps to reduce emissions six months ago, there has been a slight increase in the earthworm population.

Why is D wrong . It is also eliminating another cause.

The argument, in effect, is claiming that factory pollution has ruined the red worms' camouflage, and so the red worms, which have become more vulnerable to predators, are dying in larger numbers. We know that the ratio of red worms to black worms has decreased from 5:1 to nearly 1:1, but we don't know for sure that the factory built in 1990 is the culprit. Causality arguments are often weakened by positing that something else is the true cause, (and thereby strengthened by showing that something else is not the cause.)

C Tell us that climate conditions favored the red worm. Had it been the case that climate conditions over this time period imperiled the survival of the red worm then we would have our alternative cause. But if climate conditions favored the red worm, it strengthens the conclusions that it was, in fact, the factory pollution that was responsible.

D simply tell us that the average life expectancy of the earthworms hasn't changed. If anything, this is inconsistent with what we'd expect to be the case if the argument is valid. If red worms are no longer camouflaged from their predators, they're more likely to get eaten, so consequently, their life expectancy should decrease.

OA is C not A

OA is C not A

OA is C not A

OA is C not A

You're right. I goofed. (I Just edited my previous post accordingly.) Let this be a lesson about rushing through Critical Reasoning too quickly

anksm22 wrote:Two types of earthworm, one black and one red-brown, inhabit the woods near the town of Millerton. Because the red-brown worm's coloring affords it better camouflage from predatory birds, its population in 1980 was approximately five times that of the black worm. In 1990, a factory was built in Millerton and emissions from the factory blackened much of the woods. The population of black earthworms is now almost equal to that of the red-brown earthworm, a result, say local ecologists, solely stemming from the blackening of the woods.

Which of the following, if true, would most strengthen the conclusion of the local ecologists?

A]The number of red-brown earthworms in the Millerton woods has steadily dropped since the factory began operations.
B]The birds that prey on earthworms prefer black worms to red-brown worms.
C]Climate conditions since 1990 have been more favorable to the survival of the red-brown worm than to the black worm.
D] The average life span of the earthworms has remained the same since the factory began operations.
E]Since the factory took steps to reduce emissions six months ago, there has been a slight increase in the earthworm population.

Premises:
The number of red worms used to be five times the number of black worms, but now the number of red worms is equal to the number of black worms.
Emissions from the factory have blackened the woods.
Conclusion:
The blackening of the woods has CAUSED the number of red worms to become equal to the number of black worms.

This is a CAUSAL argument.
In a causal argument, events A and B are observed together, and the argument concludes that A causes B.
Here, the blackening of the woods and the change in the worm population are observed together, and the argument concludes that the blackening of the woods CAUSED the number of red worms to become equal to the number of black worms.

One way to strengthen a causal argument is to RULE OUT another possible cause.
C: Climate conditions since 1990 have been more favorable to the survival of the red-brown worm than to the black worm.
This option rules out climate as a possible explanation for the apparent decrease in the red worm population, STRENGTHENING the conclusion that the BLACKENING OF THE WOODS caused the number of red worms to become equal to the number of black worms.

The correct answer is C.

Why is D wrong . It is also eliminating another cause.

D: The average life span of the earthworms has remained the same since the factory began operations.
This option seems to contradict the PREMISE that the ratio of red worms to black worms has CHANGED:
If the average life span for all earthworms has remained THE SAME, then the number of red worms should still be five times the number of black worms.
A premise is a FACT; it cannot be contradicted.
Eliminate D.

Thank you Mitch . I see that now it is fact said in a different way.

The lesson here is that conclusion is KING.

Meanwhile, would A be a valid choice for ASSUMPTION / INFERENCE?

Thanks for your feedback

DavidG@VeritasPrep wrote:The argument, in effect, is claiming that factory pollution has ruined the red worms' camouflage, and so the red worms, which have become more vulnerable to predators, are dying in larger numbers. We know that the ratio of red worms to black worms has decreased from 5:1 to nearly 1:1, but we don't know for sure that the factory built in 1990 is the culprit. Causality arguments are often weakened by positing that something else is the true cause, (and thereby strengthened by showing that something else is not the cause.)

C Tell us that climate conditions favored the red worm. Had it been the case that climate conditions over this time period imperiled the survival of the red worm then we would have our alternative cause. But if climate conditions favored the red worm, it strengthens the conclusions that it was, in fact, the factory pollution that was responsible.

I agree C supports the needed assumptions of causal argument.

but I selected A based on population aspect and then worried why it is wrong based on OA.
Just explain whether my thinking as explained below is correct or wrong.

(The Bl population is equal to RB population.....i.e., RB=Bl

either
RB decreased with Bl being const
or
Bl increased with RB being const
to reach this scenario.)

Which of the following, if true, would most strengthen the conclusion of the local ecologists?

A. The number of red-brown earthworms in the Millerton woods has steadily dropped since the factory began operations.
(we have no info whether Bl also decreased rapidly along with RB because of factory pollution even if camouflaging helps them survive a bit. if that is the case then we cant say strengthen the conclusion. we have no info whether it remains constant or increases as well. This supports but not completely)

Mechmeera wrote:

DavidG@VeritasPrep wrote:The argument, in effect, is claiming that factory pollution has ruined the red worms' camouflage, and so the red worms, which have become more vulnerable to predators, are dying in larger numbers. We know that the ratio of red worms to black worms has decreased from 5:1 to nearly 1:1, but we don't know for sure that the factory built in 1990 is the culprit. Causality arguments are often weakened by positing that something else is the true cause, (and thereby strengthened by showing that something else is not the cause.)

C Tell us that climate conditions favored the red worm. Had it been the case that climate conditions over this time period imperiled the survival of the red worm then we would have our alternative cause. But if climate conditions favored the red worm, it strengthens the conclusions that it was, in fact, the factory pollution that was responsible.

I agree C supports the needed assumptions of causal argument.

but I selected A based on population aspect and then worried why it is wrong based on OA.
Just explain whether my thinking as explained below is correct or wrong.

(The Bl population is equal to RB population.....i.e., RB=Bl

either
RB decreased with Bl being const
or
Bl increased with RB being const
to reach this scenario.)

Which of the following, if true, would most strengthen the conclusion of the local ecologists?

A. The number of red-brown earthworms in the Millerton woods has steadily dropped since the factory began operations.
(we have no info whether Bl also decreased rapidly along with RB because of factory pollution even if camouflaging helps them survive a bit. if that is the case then we cant say strengthen the conclusion. we have no info whether it remains constant or increases as well. This supports but not completely)

You've got the gist of it, but notice the language used in the conclusion: The population of black earthworms is now almost equal to that of the red-brown earthworm, a result, say local ecologists, SOLELY stemming from the blackening of the woods.

Just because the population of the red-brown worm has decreased steadily since the factory opened doesn't mean that the factory was the ONLY cause of the decrease. What if there had been another environmental change that happened around the same time the factory opened, and this other environmental change contributed to the population decrease of the red-brown worm? Answer choice A leaves such a possibility open, whereas C tell us explicitly that this was not the case.

DavidG@VeritasPrep wrote:

Mechmeera wrote:

DavidG@VeritasPrep wrote:The argument, in effect, is claiming that factory pollution has ruined the red worms' camouflage, and so the red worms, which have become more vulnerable to predators, are dying in larger numbers. We know that the ratio of red worms to black worms has decreased from 5:1 to nearly 1:1, but we don't know for sure that the factory built in 1990 is the culprit. Causality arguments are often weakened by positing that something else is the true cause, (and thereby strengthened by showing that something else is not the cause.)

C Tell us that climate conditions favored the red worm. Had it been the case that climate conditions over this time period imperiled the survival of the red worm then we would have our alternative cause. But if climate conditions favored the red worm, it strengthens the conclusions that it was, in fact, the factory pollution that was responsible.

I agree C supports the needed assumptions of causal argument.

but I selected A based on population aspect and then worried why it is wrong based on OA.
Just explain whether my thinking as explained below is correct or wrong.

(The Bl population is equal to RB population.....i.e., RB=Bl

either
RB decreased with Bl being const
or
Bl increased with RB being const
to reach this scenario.)

Which of the following, if true, would most strengthen the conclusion of the local ecologists?

A. The number of red-brown earthworms in the Millerton woods has steadily dropped since the factory began operations.
(we have no info whether Bl also decreased rapidly along with RB because of factory pollution even if camouflaging helps them survive a bit. if that is the case then we cant say strengthen the conclusion. we have no info whether it remains constant or increases as well. This supports but not completely)

You've got the gist of it, but notice the language used in the conclusion: The population of black earthworms is now almost equal to that of the red-brown earthworm, a result, say local ecologists, SOLELY stemming from the blackening of the woods.

Just because the population of the red-brown worm has decreased steadily since the factory opened doesn't mean that the factory was the ONLY cause of the decrease. What if there had been another environmental change that happened around the same time the factory opened, and this other environmental change contributed to the population decrease of the red-brown worm? Answer choice A leaves such a possibility open, whereas C tell us explicitly that this was not the case.

I get the point. But can we eliminate A for below reason.

we have no info whether Black also decreased rapidly along with RB because of factory pollution even if camouflaging helps them survive a bit. we have no info whether it remains constant or increases as well.

I get the point. But can we eliminate A for below reason.

Quote:
we have no info whether Black also decreased rapidly along with RB because of factory pollution even if camouflaging helps them survive a bit. we have no info whether it remains constant or increases as well.

Ultimately, you'll end up with the same reasoning. We know that the ratio of red:black worms has gone from 5:1 to 1:1. That's a given. It's true that A doesn't tell us how the factory pollution is affecting the black worm, but there's no reason to believe that the black worm would be directly impacted. It's the red worm, after all, that was camouflaged and stood to lose that camouflage because of the pollution. The black worm, so far as we know, has no camouflage to lose, so there's no reason to believe that the factory pollution would cause more of them to die. But even if you wanted to argue that the pollution was somehow impacting the population of black worms via some unnamed mechanism, we still have the ratio change to account for, leading us to suspect that another environmental factor could be responsible for reducing the population of red worms. Any way you analyze it, it's the uncertainty about the possible alternative cause that makes A incorrect.

DavidG@VeritasPrep wrote:The argument, in effect, is claiming that factory pollution has ruined the red worms' camouflage, and so the red worms, which have become more vulnerable to predators, are dying in larger numbers. We know that the ratio of red worms to black worms has decreased from 5:1 to nearly 1:1, but we don't know for sure that the factory built in 1990 is the culprit. Causality arguments are often weakened by positing that something else is the true cause, (and thereby strengthened by showing that something else is not the cause.)

C Tell us that climate conditions favored the red worm. Had it been the case that climate conditions over this time period imperiled the survival of the red worm then we would have our alternative cause. But if climate conditions favored the red worm, it strengthens the conclusions that it was, in fact, the factory pollution that was responsible.

D simply tell us that the average life expectancy of the earthworms hasn't changed. If anything, this is inconsistent with what we'd expect to be the case if the argument is valid. If red worms are no longer camouflaged from their predators, they're more likely to get eaten, so consequently, their life expectancy should decrease.

Hi David, thanks for the clear explanation. Would you kindly explain why C is preferable over B, given that in both B and C, basically there is some factor going against the survival of the black worm (in B, the birds's preference for black worms and in C, the unfavorable climate) but its population has still survived/grown, strengthening the conclusion that the better camouflage due to the blackened woods enabled it to do so? If C were to be evaluated alone, it would be the clear choice. However, when seen next to each other, both seem to be the likely choice.

Phoenix7 wrote:

DavidG@VeritasPrep wrote:The argument, in effect, is claiming that factory pollution has ruined the red worms' camouflage, and so the red worms, which have become more vulnerable to predators, are dying in larger numbers. We know that the ratio of red worms to black worms has decreased from 5:1 to nearly 1:1, but we don't know for sure that the factory built in 1990 is the culprit. Causality arguments are often weakened by positing that something else is the true cause, (and thereby strengthened by showing that something else is not the cause.)

C Tell us that climate conditions favored the red worm. Had it been the case that climate conditions over this time period imperiled the survival of the red worm then we would have our alternative cause. But if climate conditions favored the red worm, it strengthens the conclusions that it was, in fact, the factory pollution that was responsible.

D simply tell us that the average life expectancy of the earthworms hasn't changed. If anything, this is inconsistent with what we'd expect to be the case if the argument is valid. If red worms are no longer camouflaged from their predators, they're more likely to get eaten, so consequently, their life expectancy should decrease.

Hi David, thanks for the clear explanation. Would you kindly explain why C is preferable over B, given that in both B and C, basically there is some factor going against the survival of the black worm (in B, the birds's preference for black worms and in C, the unfavorable climate) but its population has still survived/grown, strengthening the conclusion that the better camouflage due to the blackened woods enabled it to do so? If C were to be evaluated alone, it would be the clear choice. However, when seen next to each other, both seem to be the likely choice.

Think of it this way. Initially, the red worms are thriving relative to black worms. Then, something changes, and suddenly the red worms are getting devoured just as often as the black worms. So what happened?

So the general thrust of the argument is that the change that caused this turn of events was factory pollution. As an arrow diagram, you could think of it like this: factory pollution ----> red worms die off

To strengthen this, we'd like to show that there wasn't something else, a different change, that could have caused the red worms to die off.

C lets us know that a change in climate conditions was not responsible.

So now we can rule out: change in climate ---> red worms die off, thus strengthening our initial arrow diagram.

Notice that B doesn't offer anything that's changed since 1980. How can the fact that the birds have always referred black worms to red-brown worms account for the population shift? Put another way, what alternative cause, aside from factory pollution could be ruled out based on this preference? Remember that the argument tells us explicitly that the reason there are more red worms initially is that they have better camouflage, not because of the birds' eating preference.