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Re: Researchers have long noted strange grooves near the gum lines on [#permalink]
Researchers have long noted strange grooves near the gum lines on dental remains of some early humans. The marks are absent from the teeth of modern-day toothpick users, and have therefore been assumed not to present evidence of tooth picking where they have been present. But an anthropologist has recently proposed that the early humans used grass stalks, which, unlike wood, contain abrasive silica, a substance that would facilitate the development of the grooves.

Which of the following would, if found to be true, be most useful to the evaluation of the anthropologist's hypothesis?

A. The dental remains that have the type of grooves in question almost as commonly show signs of tooth decay as do the remains that lack the grooves.

B. Dental remains of some of the early humans without the grooves have been found at places where the available grass could have been suitable for tooth picking during their lifetimes.

C. Unlike grass stalks, few modern-day toothpicks contain significant amounts of abrasive silica.

D. Abrasive silica derived from grasses and other, similar plants could be useful in the removal of cavity-causing plaque from humans' teeth.

E. The grooves occur on the teeth of some early humans whose remains were found at places where no grass suitable for tooth picking would have been obtainable during their lifetimes.


The passage talks about certain gum marks found in early humans but not in humans today who do tooth picking. Although this may suggest early humans did not do tooth picking, an anthropologist's theory is that this could be because early humans used grass stalks. The idea being that grass stalks have an abrasive substance (unlike wood) that would help cause these marks.

We're asked to look for something that would help in evaluating the anthropologist's theory

(E) is the answer. If early humans - in an area where there is no grass for tooth picking STILL had these gum marks - it would mean something ELSE was the cause.

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Researchers have long noted strange grooves near the gum lines on [#permalink]
MartyMurray wrote:
The anthropologist's hypothesis is the following:

the early humans used grass stalks [for tooth picking]

The support for that hypothesis is the following:

[The grass stalks] unlike wood, contain abrasive silica, a substance that would facilitate the development of the grooves

The correct answer must be "useful to the evaluation of the anthropologist's hypothesis."

Since the answer choices are statements, the correct answer will simply weaken or strengthen the argument.

A. The dental remains that have the type of grooves in question almost as commonly show signs of tooth decay as do the remains that lack the grooves.

This choice has no effect on the argument. The fact that the dental remains show signs of tooth decay does not indicate anything about what caused the grooves or whether the early humans used grass stalks for tooth picking. After all, dental decay could occur regardless of whether they did or didn't use grass stalks for tooth picking.

Eliminate.

B. Dental remains of some of the early humans without the grooves have been found at places where the available grass could have been suitable for tooth picking during their lifetimes.

The fact that grass suitable for tooth picking may have existed where early humans' teeth did not have the grooves doesn't tell us whether the grooves were caused by use of grass for cleaning teeth. After all, it's not the case that all early humans must have used the available resources in the same way. It's likely that some early humans didn't use grass to clean their teeth.

Eliminate.

C. Unlike grass stalks, few modern-day toothpicks contain significant amounts of abrasive silica.

This information has already been provided by the passage. The passage indicates that grass stalks are "unlike" modern toothpicks in that grass stalks contain silica. Information already provided cannot have any new effect on the argument.

Eliminate.

D. Abrasive silica derived from grasses and other, similar plants could be useful in the removal of cavity-causing plaque from humans' teeth.

This choice has no effect on the argument. The fact that abrasive silica derived from grasses and other, similar plants could be useful in the removal of cavity-causing plaque doesn't mean that early humans used abrasive silica or grass stalks containing abrasive silica to clean their teeth.

Eliminate.

E. The grooves occur on the teeth of some early humans whose remains were found at places where no grass suitable for tooth picking would have been obtainable during their lifetimes.

This choice weakens the argument. We see that the effect "grooves occur on the teeth" exists where the presumed cause "grass suitable for tooth picking" did not exist. This information indicates that the use of grass for tooth picking was not the cause of the grooves since the grooves appear to have occurred even without the grass.

The correct answer is


Hi MartyMurray,

Would you think if the information in B is not true, it will weaken the argument? Thanks
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Researchers have long noted strange grooves near the gum lines on [#permalink]
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jaky_nguyen wrote:
Hi MartyMurray,

Would you think if the information in B is not true, it will weaken the argument? Thanks

Here's (B).

B. Dental remains of some of the early humans without the grooves have been found at places where the available grass could have been suitable for tooth picking during their lifetimes.

Here's the negation of (B).

B. No dental remains of early humans without the grooves have been found at places where the available grass could have been suitable for tooth picking during their lifetimes.

If anything, that negated version of (B) would strengthen the argument a little, by showing that, wherever grass that could have been suitable for tooth picking existed, early humans had the grooves and that, wherever dental remains without the grooves were found, there hadn't been grass that could have been suitable for tooth picking. That information would indicate that the grass was connected to the grooves in teeth and thus to tooth picking.
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Researchers have long noted strange grooves near the gum lines on [#permalink]
Hi, 

For option B, in the question prompt it has been mentioned that grass stalks contain silica, however, in option B it has been mentioned that toothpicks contain silica but in the explanation for option B it's eliminated by stating that the information is already present in the prompt. I am a bit confused regarding this option. Can someone please explain.

Thanks.­
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Researchers have long noted strange grooves near the gum lines on [#permalink]
MartyMurray wrote:
The anthropologist's hypothesis is the following:

the early humans used grass stalks [for tooth picking]

The support for that hypothesis is the following:

[The grass stalks] unlike wood, contain abrasive silica, a substance that would facilitate the development of the grooves

The correct answer must be "useful to the evaluation of the anthropologist's hypothesis."

Since the answer choices are statements, the correct answer will simply weaken or strengthen the argument.

A. The dental remains that have the type of grooves in question almost as commonly show signs of tooth decay as do the remains that lack the grooves.

This choice has no effect on the argument. The fact that the dental remains show signs of tooth decay does not indicate anything about what caused the grooves or whether the early humans used grass stalks for tooth picking. After all, dental decay could occur regardless of whether they did or didn't use grass stalks for tooth picking.

Eliminate.

B. Dental remains of some of the early humans without the grooves have been found at places where the available grass could have been suitable for tooth picking during their lifetimes.

The fact that grass suitable for tooth picking may have existed where early humans' teeth did not have the grooves doesn't tell us whether the grooves were caused by use of grass for cleaning teeth. After all, it's not the case that all early humans must have used the available resources in the same way. It's likely that some early humans didn't use grass to clean their teeth.

Eliminate.

C. Unlike grass stalks, few modern-day toothpicks contain significant amounts of abrasive silica.

This information has already been provided by the passage. The passage indicates that grass stalks are "unlike" modern toothpicks in that grass stalks contain silica. Information already provided cannot have any new effect on the argument.

Eliminate.

D. Abrasive silica derived from grasses and other, similar plants could be useful in the removal of cavity-causing plaque from humans' teeth.

This choice has no effect on the argument. The fact that abrasive silica derived from grasses and other, similar plants could be useful in the removal of cavity-causing plaque doesn't mean that early humans used abrasive silica or grass stalks containing abrasive silica to clean their teeth.

Eliminate.

E. The grooves occur on the teeth of some early humans whose remains were found at places where no grass suitable for tooth picking would have been obtainable during their lifetimes.

This choice weakens the argument. We see that the effect "grooves occur on the teeth" exists where the presumed cause "grass suitable for tooth picking" did not exist. This information indicates that the use of grass for tooth picking was not the cause of the grooves since the grooves appear to have occurred even without the grass.

The correct answer is

­MartyMurray, I would think that for an "evaluate" question, the answer choice does not have to strongly prove or disprove the conclusion, so in this case it only needs to affect ie. strengthen or weaken the hypothesis.
For B: - if that info is true, it would weaken the hypothesis a little since there's remains without grooves where there's grass available, so maybe the grass does not cause the grooves. Again, there could be many other factors, but all else being the same, shouldn't it weaken the hypothesis?
- If the info is false ie. negation, that would strengthen the hypothesis a little, as you already explained.

I can see the same pattern for E. So in this case I'm struggling to see why E is better than B at all. Can someone help?­
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Researchers have long noted strange grooves near the gum lines on [#permalink]
Expert Reply
tribui wrote:
MartyMurray wrote:
B. Dental remains of some of the early humans without the grooves have been found at places where the available grass could have been suitable for tooth picking during their lifetimes.

The fact that grass suitable for tooth picking may have existed where early humans' teeth did not have the grooves doesn't tell us whether the grooves were caused by use of grass for cleaning teeth. After all, it's not the case that all early humans must have used the available resources in the same way. It's likely that some early humans didn't use grass to clean their teeth.

Eliminate.­

­MartyMurray, I would think that for an "evaluate" question, the answer choice does not have to strongly prove or disprove the conclusion, so in this case it only needs to affect ie. strengthen or weaken the hypothesis.
For B: - if that info is true, it would weaken the hypothesis a little since there's remains without grooves where there's grass available, so maybe the grass does not cause the grooves. Again, there could be many other factors, but all else being the same, shouldn't it weaken the hypothesis?
- If the info is false ie. negation, that would strengthen the hypothesis a little, as you already explained.

I can see the same pattern for E. So in this case I'm struggling to see why E is better than B at all. Can someone help?­

Notice that the conclusion of the argument is about the cause of the grooves in teeth in which the grooves are present. Some people say that cause of the grooves is not tooth picking, but this one anthropologist has proposed that picking with abrasive grass stalks caused the grooves.

So, it doesn't really weaken the argument to say, "Dental remains of some of the early humans without the grooves have been found at places where the available grass could have been suitable for tooth picking during their lifetimes," because it's fairly clear that picking with abrasive grass would cause grooves. After all, picking one's teeth with something abrasive would result in tooth wear.

So, the fact that some abrasive grass was present where the teeth do not have grooves shows only that those people did not pick their teeth with grass, not that picking with grass is not the cause of the grooves. Right?

Here's a similar example.

Let's say that we found a tree that had been cut down by an animal. We see beavers in the same area. So, we hypothesize that a beaver cut down the tree. The fact that other trees are still standing where beavers are present would not mean that the tree that had been cut down had not been cut down by a beaver. It would just mean that the beaver had not cut down every tree.

So, this is a similar situation. We don't need all teeth where grass was present to have grooves in order to conclude that grass caused the grooves in teeth that do have grooves.

Thus, the answer to (B) neither weakens nor strengthens the argument.­
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Re: Researchers have long noted strange grooves near the gum lines on [#permalink]
GMATNinja - Can you please help in explaining option choice B and E. For me grass stalks caused the grooves in the early humans.

B. Dental remains of some of the early humans without the grooves have been found at places where the available grass could have been suitable for tooth picking during their lifetimes.
From B option choice are we interpreting that those people could have used tooth picking but they didnt use and hence no grooves? Hence, this is acting as a strengthener?­
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Re: Researchers have long noted strange grooves near the gum lines on [#permalink]
Understanding the argument - 
­Researchers have long noted strange grooves near the gum lines on dental remains of some early humans. - Background info. 

The marks are absent from the teeth of modern-day toothpick users, and have therefore been assumed not to present evidence of tooth picking where they have been present. - Premise and some general claim. Normally, after the general claim, the author will present a contrast. Basically, it says that modern-day toothpick users don't have grooves, so having grooves leads to an assumption that they may not have used toothpicks. 

But an anthropologist has recently proposed that the early humans used grass stalks, which, unlike wood, contain abrasive silica, a substance that would facilitate the development of the grooves. - "but" introduces a contrast. The anthropologist proposes that this is not the case; they didn't use the toothpick and may have used a different type than the wooden ones we see now. He says they may have used the toothpicks made from grass stalks and in using those tooth picks they got the grooves. So essentially it challenges the assumption of having goorves means no toothpicks. 

Which of the following would, if found to be true, be most useful to the evaluation of the anthropologist's hypothesis? 

Option Elimiantion - What would be most useful to evaluate the anthropologist's hypothesis? We have grass stalks and they cause groves. So what happens without grass stalks? they should not have grooves? Right? Yes. But if that's not the case then the argument fall apart. 

A. The dental remains that have the type of grooves in question almost as commonly show signs of tooth decay as do the remains that lack the grooves. - this comparison is out of scope. 

B. Dental remains of some of the early humans without the grooves have been found at places where the available grass could have been suitable for tooth picking during their lifetimes. - Hypothesis is not about grass always causing grooves. There is no sufficiency established in the hypothesis that if there is grass, there will be groooves. So there is always a possibility that there is grass and there may not be grooves. It doesn't necessarily contradict with the hypothesis. What we need is what happens when there is no grass. Distortion. 

C. Unlike grass stalks, few modern-day toothpicks contain significant amounts of abrasive silica. - Out of scope. 

D. Abrasive silica derived from grasses and other, similar plants could be useful in the removal of cavity-causing plaque from humans' teeth. - none of our concern. Out of scope. 

E. The grooves occur on the teeth of some early humans whose remains were found at places where no grass suitable for tooth picking would have been obtainable during their lifetimes. - Meaning, grooves are still happening without grass which calls the anthropologists hypothesis into question. ok. 
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Re: Researchers have long noted strange grooves near the gum lines on [#permalink]
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