About two million years ago, lava dammed up a river in western Asia

I am still confused why option C is wrong. Can somebody explain option C in more detail that why it's wrong?

2m yrs ago ---> lava dammed up a river = Formation of a small lake Lake existed till 1.5 m yrs ago Human bones found in the sediments on top of the layer of lava. Ancestors of Modern Humans lived = 2 m to 1.5 m years ago.

Try to negate option (E)

The bones were not there in the sediments by the time the lake disappeared = Bones were brought from somewhere and added to the lake sediments.

This clearly makes the argument fall apart....

Hence answer is no doubt about (E)

vnigam21

About two million years ago, lake formed

The lake existed for about 0.5 million years and Bones were recently found in the lake-bottom sediments on top of the layer of lava.

Conclusion: Therefore, ancestors of modern humans lived in Western Asia between 2 million and 1.5 million years ago.

Do you get the gap of assumption in between the statements?

By the time of discovery, the bones were already there.

Since we got the bones at lake bottom it is understood that lake has dried up and if the conclusion that humans lived between that time period then the bones were already in the sediments by the time the lake disappeared/dried up.

so E is clearly visible as a right choice.

coming to C,
(C) The lava under the lake-bottom sediments did not contain any human fossil remains............

The fact that lava does not contain fossil remains while its seidments contain the fossil does not help anyway.

Even if we negate the statement i.e.,

The lava under the lake-bottom sediments do contain any human fossil remains. This supports the conclusion if not anything. This negation test proves that this cannot be the assumption...

I hope this helps

Premise:- About two million years ago, lava dammed up a river in western Asia and caused a small lake to form. The lake existed for about half a million years. Bones of an early human ancestor were recently found in the ancient lake-bottom sediments on top of the layer of lava.
Conclusion: - Therefore, ancestors of modern humans lived in Western Asia between 2 million and 1.5 million years ago.

Which one of the following is an assumption required by the argument?

(A) There were not other lakes in the immediate area before the lava dammed up the river. - irrelevant

(B) The lake contained fish that the human ancestors could have used for food. - Irrelevant

(C) The lava under the lake-bottom sediments did not contain any human fossil remains - This is a trap answer if you read too fast as the premise states human remains were found on top sediments in lake bottom. Irrespective of the location with respect to lava layer this is not an assumption rather a mere statement of fact hence incorrect choice.

(D) The lake was deep enough that a person could drown in it - This is not an assumption rather a property of the lake and does not support the conclusion that humans existed because their remains were found in the lake.

(E) The bones were already in the sediments by the time the lake disappeared - Correct! This is the assumption that the author bases his/her conclusion on. The author assumes that human remains were already in the sediment on or before the lake disappeared on which basis the conclusion that humans existed when the lake existed is arrived at.

General Description: This question asks you to find the assumption required by the argument. In other words, find the statement whose truth is required if the argument is to succeed in demonstrating its conclusion.

A. Incorrect. The existence of other lakes in the area is irrelevant to the argument.

B. Incorrect. If response (B) turned out to be true, that might provide a reason why humans were in the area of the lake, but this particular explanation need not be assumed in order for the argument to succeed in demonstrating its conclusion.
C. Incorrect. It does not matter for the argument whether or not there were such remains in the lava, and the argument does not state or imply that there were no humans in the region prior to two million years ago. This was by far the most popular incorrect response.

D. Incorrect. The remains could have gotten into the lake in any number of other ways; to give just one, perhaps the people in the area put their dead into the lake.

E. Correct. If the bones were not already in the sediments when the lake dried up, that means that they got into the sediments later; that is, less than one-and-a-half million years ago. But then their existence would not provide evidence that there were human ancestors in western Asia between two million and one-and-a-half million years ago; that is, the conclusion of the argument would not follow if (E) is false.

Difficulty Level: Medium difficulty

Tips and Pitfalls: Another way to think about the question of whether an assumption is required by an argument is to think about what happens to the argument if the assumption turns out to be false. If the argument cannot possibly succeed when the assumption is false, then the assumption is required by the argument. Also, when asked for a necessary assumption, be careful not to pick an assumption that is stronger or broader than what is strictly necessary for the argument to succeed, even if making that assumption might strengthen the argument.

Yeah, really good question. What makes that a non-issue here is that the extra specificity ("EARLY human ancestor") comes in the premise, and the less-specific piece ("human ancestor") is in the conclusion. Because the conclusion only needs evidence of "an ancestor" in order to hold, then any subset of "ancestor" (whether early ancestor, male ancestor, female ancestor, etc.) can serve as evidence of that more-general conclusion.

If it were the other way around you've got a great point (so I love that you're thinking that way) - if we were trying to prove that early human ancestors lived in this place/time and our only evidence was "bones of an ancestor" then we have a mismatch - how do we know that our bones are from an early ancestor? But here the conclusion isn't as specific - we only need "an ancestor" - so the fact that the premise specifies which type of ancestor doesn't hurt the conclusion.

Hmm, that's a pretty good question. A couple replies:

1) Let me ask you this: isn't it an assumption to say that "because he knows it's an EARLY ancestor, he knows the date range"?

Like take me: if I were in a museum and saw a Cro-Magnon Man skeleton next to a normal human skeleton, I could probably tell you "hey that one is from an early human ancestor" but I couldn't put a date on it. (Dinosaurs...same thing)

2) Way more importantly, that doesn't really matter. The conclusion is that "ancestors of modern humans lived in Western Asia between 2 million and 1.5 million years ago." Even if the bones are carbon-dated to be between 2 million and 1.5 million years ago we've only satisfied half the conclusion - the age, but not the location. If the bones had ended up there tens of thousands of years later - say, emperors in Western Asia raided a museum in Eastern Europe and transported the bones back home - then the conclusion is off.

(Note: there was actually an episode of The Simpsons where a shopping center "faked" the bones of an angel in the area that was to become the mall in order to get press around the opening, so maybe this is easier for me to visualize! But hopefully the point remains - we need to know that the bones are evidence of time AND place...I'm not 100% convinced that knowledge of "early" is enough to get us time, but even if it were we're still assuming a bit on place)

About two million years ago, lava dammed up a river in western Asia and caused a small lake to form. The lake existed for about half a million years. Bones of an early human ancestor were recently found in the ancient lake-bottom sediments on top of the layer of lava.

Conclusion: Therefore, ancestors of modern humans lived in Western Asia between 2 million and 1.5 million years ago.

Which one of the following is an assumption required by the argument?

(A) There were not other lakes in the immediate area before the lava dammed up the river...............we are not concerned about other lakes. OFS

(B) The lake contained fish that the human ancestors could have used for food...............human existence needs to be proved their food can be anything not only fish.

(C) The lava under the lake-bottom sediments did not contain any human fossil remains............sediments on top of lava does not mean that lava did not contain any fossil. This need not be assumed as this does not affect the conclusion.

(D) The lake was deep enough that a person could drown in it..................person death by drowning need not be assumed, he can die anywhere by any means and his fossil may have just floated in air to the lake.

(E) The bones were already in the sediments by the time the lake disappeared.............this is must to be assumed.

Here is a video explanation of this question by Ravi Sreerama,

https://www.youtube.com/watch?v=_HxvVaBqa08&index=4&list=PL8IRdvEjAM5LsQWiqVpmsQKz0wBKzbDdr

I understand option E.

If i negate option C the lava under the lake-bottom sediments did contain human fossils.

Doesnt this break the conclusion?

Dear VeritasPrepBrian VeritasKarishma IanStewart,

I think what confuses many students is the phrase EARLY human ancestor in the stimulus.

So, if there existed humans BEFORE 2 million years ago, can we still call the humans lived BETWEEN 2 million and 1.5 million years ago EARLY?

Thank you in advance!

Dear VeritasPrepBrian,

Thank you for your kind words

I have one more question from the above. Pardon me if I ask too much.

I am not sure how to interpret this sentence in the passage: Bones of an EARLY human ancestor were recently found in the ancient lake-bottom sediments on top of the layer of lava.

The premise mentions Bones of an EARLY human ancestor. In order to legitimately mention that, the author needs to know the (approximate) age of the bones which is presumably between 2 million and 1.5 million years ago.

So, in light of the NEGATED choice E., someone put the bones which is 2 million and 1.5 million years old in that sediment? That person cannot put the young bones in it because we know that the bones is very very old?

Thank you Sir!

VeritasPrepBrian
(E) The bones were already in the sediments by the time the lake disappeared.

Can't these bones be there in the sediments prior to 2 million years ago? If so, then we can not definitely conclude that ancestors lived during the time-period of 2 mn to 1.5 mn years ago time-frame.

They must have lived even prior to 2 mn years ago died before that and the bones have been there since then. They didn't actually live during that time-frame.

I am pretty sure I am missing something (May be since it was river prior to 2 mn years ago, noone could have lived at that location? And that it was only after 2 mn years ago that anyone could have ever lived in that particular location in Western Asia where the sediments were found?)

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