The fossil record indicates that the teeth of many early hominids

Question

The fossil record indicates that the teeth of many early hominids, particularly males, have wear grooves in certain locations between adjacent teeth. According to the most influential view, toothpick use explains the known distribution and anatomical placement of these grooves. Consequently, the wear grooves have been taken to hold important clues to early hominid diet and oral hygiene habits. However, the tooth-picking hypothesis may not be the proper explanation since ________.

Which of the following most logically completes the passage?

A. some fossils of hominid children have been found with teeth free of wear grooves
B. it fails to explain why wear grooves are found on some teeth of early hominids but not on some of their other teeth
C. the grooves could just as likely have resulted from using the teeth to strip grain from stalks
D. evidence shows that some female hominids had little access to foods that would stick in teeth
E. modern toothpicks are designed in a way that does not cause wear grooves

smithgmat123 · Answer

The most logical completion for the passage is: "the grooves could just as likely have resulted from using the teeth to strip grain from stalks".

Aprilhaa · Answer

I can see why C is attractive, since it provides an alternative explanation for the grooves. However, I’m struggling to see why it would rule out the toothpick hypothesis. Even if some grooves could have resulted from using teeth to strip grain from stalks, couldn’t others still have been caused by toothpick use? In other words, C seems to offer a possible alternative cause rather than showing that the toothpick hypothesis is not the proper explanation.😊

Adit_ · Answer

The stem says X->Y, meaning X leads to Y and the way you complete the passage is by finding a weakener that weakens that link. Option C is the only one that weakens the link. You need not have 100% certainty, you just need a statement that gives doubt of the stated link.

Also if you notice all other options are more or less entirely wrong and can simply not complete the passage.

Option B may look attractive but the whole stem is for grooves in "certain" locations. So B does not weaken it.

Aprilhaa · Answer

Thanks! You’ve been so helpful.

egmat · Answer

Hi @Aprilhaa,

Your instinct here is sharp, and you're right about one thing: C does  not  prove that toothpicks never caused any grooves. Some grooves could still be from toothpick use, hold onto that, it's a correct reading.

The slip is in what the question is actually asking for. The blank completes "the tooth-picking hypothesis  may not be the proper explanation  since ___." You're testing C against a much harder bar: does it eliminate toothpicks entirely? But the passage never asks you to eliminate toothpicks. It only asks for a reason to doubt that toothpicks are  the  explanation.

The work is done by three words in C:  "just as likely."  If grain-stripping is just as likely to have made the grooves, then there's no longer any reason to single out toothpicks as the proper explanation, because the two causes sit on equal footing. That's exactly what "may not be the proper explanation" needs: a rival that's equally good, not a knockout that rules toothpicks out.

Watch how the strength of that phrase decides everything. Turn the one knob:

> always resulted from grain-stripping  : too strong, more than the passage needs.
 > could conceivably have resulted from it  : too weak; a bare possibility wouldn't dent the leading view.
 > "just as likely"  : the sweet spot, equal plausibility is enough.

So  you don't need certainty. You need a reason for doubt, and an equally likely alternative is exactly that.

Aprilhaa · Answer

Thank you so much for taking the time to write such a detailed explanation. This was extremely helpful.

I think my mistake was exactly what you pointed out: I was testing whether C could eliminate the toothpick hypothesis entirely, rather than asking whether it could make toothpicks no longer the best explanation.

Your explanation of the phrase “just as likely” really made the distinction click for me. The comparison with “always resulted from” and “could conceivably have resulted from” was especially useful.

I appreciate the effort you put into this. It clarified not only this question, but also a broader CR principle about competing explanations and strength calibration.

TheAdmissionHub · Answer

Premises  
1. Many early hominids’ teeth (especially males) show wear grooves in specific locations between adjacent teeth. 
2. A widely accepted hypothesis claims that toothpick use explains the known distribution of the grooves. 
3. Because of that, the grooves have been treated as clues to diet and oral hygiene habits.

Conclusion  
The tooth-picking hypothesis may not be the proper explanation since...

Note the final connector!  Now we need a reason weakening the claim that the grooves reveal toothpick use and related habits. 
Which of the following most logically completes the passage?

A) some fossils of hominid children have been found with teeth free of wear grooves 
 Wrong:  This is about a particular group  (children)  and it doesn’t explain why the tooth-picking hypothesis may not be the proper explanation for the distribution and anatomical placement of those grooves; besides, children may be too young to have grooves and are not a good example to weaken the hypothesis.

B) it fails to explain why wear grooves are found on some teeth of early hominids but not on some of their other teeth 
 Wrong:  The original hypothesis already explains a specific distribution of grooves, so this does not necessarily undermine it.

C) the grooves could just as likely have resulted from using the teeth to strip grain from stalks 
 Correct: this suggests an alternative cause that would justify the presence of grooves. Maybe the grooves could have been caused by another behaviour: stripping grain from stalks.

D) evidence shows that some female hominids had little access to foods that would stick in teeth 
 Wrong:  This may indicate  gender-related differences in diet , but it does not explain whether the toothpick hypothesis accounts for where the grooves are located and how they are distributed.

E) modern toothpicks are designed in a way that does not cause wear grooves 
 Wrong:  This argument relies on observations of  modern toothpick use  and therefore does not conclusively demonstrate that the same behavior occurred in early hominids.

The fossil record indicates that the teeth of many early hominids

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The fossil record indicates that the teeth of many early hominids

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

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My Rewards