PT63.S1.Q19 - anthropologist: it was formerly believed that

stcaitmokyu

Hi,
So I'm not sure about the correct answer C...
Why do we have to assume or compare the ancestors to Neanderthals? Why it's required?
Even though we know homo sapiens ancestors of contemporary humans was not significantly more similar to that of Neanderthals than is the DNA of people today, that only means people today was more similar to Homo sapiens when we compared to Neanderthals.
It could be true there are some similarities between ppl and Neanderthals, just not as much as with homo sapiense.
In that case, we cannot conclude homo sapiens did not interbred with Neanderthals (and it could be true both neanderthals and homo sapiens were ancestors of humans).
I'm really confused with C and do not understand why it's required to make the conclusion in the argument (which is they did not "interbreed")
https://7sage.com/lsat_explanations/lsat-63-section-1-question-19/

runiggyrun

This is a very hard question, and the only way I arrived to C was to first eliminate every other answer - fortunately the wrong answers are quite obviously wrong.
But why is C right?
There are many reasons we might consider deciding whether or not Homo Sapiens interbred with Neanderthals (proximity, presence in modern humans of traits present in Neanderthals but not Homo Sapiens, genetic compatibility between the two "old" species that would make interbreeding possible, etc).

HOWEVER, the argument only gives us one consideration, basically stating.
The DNA of current people and that of Neanderthals is quite different.
That means that the ancestors of current people did not interbreed with Neanderthals.

The only way that (somewhat fuzzy) premise supports the (very strong) conclusion is if you take it to mean "the DNA of modern humans is different enough from that of Neanderthals to make interbreeding impossible" (the same rationale you'd use to argue that horses don't interbreed with giraffes).
Notice they don't say "there's no trace of the Neanderthal's DNA in modern humans so we don't think they interbred", although that's how a lot of people would interpret the premise. They just say "there are big differences". How big? We don't know. But we do know they are big enough for a specialist to conclude there was no interbreeding.

Answer C eliminates the potential objection that maybe the DNA of homo sapiens was closer to that of Neanderthals, so even if a modern human wouldn't be able to interbreed with a Neanderthal, a homo sapiens still could.

stcaitmokyu

Thanks for reply,
but...I think I'm still confused.
First of all...What does interbreed mean? I'm afraid that I misunderstood what it means...
I thought it means different species make descendant...so it's apparantly truee the two species are totally different.
So I thought it's no need to mention Neandeltal in answer C.
Or in your explanation > Answer C eliminates the potential objection that maybe the DNA of homo sapiens was closer to that of Neanderthals, so even if a modern human wouldn't be able to interbreed with a Neanderthal, a homo sapiens still could.
I just don't understand why it is "required" to compare how much differences they have between the ancestor to N and ancestor to humans.
Sorry if my question does not make sense...I'm so confused with this question and also not sure about what I wanna ask either

runiggyrun

Interbreed means that they can mate and have viable offspring.
The reason I think this question is so hard is that I feel like it relies on people being aware that interbreeding is only possible in species that are genetically similar enough (although what's similar enough can vary greatly - for instance horses can interbreed with zebras even though they are different species with different numbers of chromosomes, but certain species of crow don't interbreed with each other).
It also relies on people somehow realizing that it's this impossibility of interbreeding when the genetic differences are too great that's the crux of the argument. Essentially you have to read the premises and "translate" them to mean
"The genetic difference between modern humans and Neanderthals are too great to make interbreeding possible, therefore we think that the difference between homo sapiens and Neanderthals were also too great to make interbreeding possible".

Once you get to that, you can see that the assumption is that the differences used to be at least as big as they are now, which is what C is saying.
It's getting to this translation that is the difficult part - I think a basic knowledge of genetics helps you interpret the premises the way the authors want you to interpret them. In the absence of such knowledge, eliminating the other answers would get you to C. Like I said, I eliminated the other answers and only when I was left with C it dawned on my why it was right, because only at that point I realized what the premise meant.

stcaitmokyu

umm...thanks. I guess I have to think about this question a little more...
but thanks!

inactive

Are you sure you're looking at PT63.S3.Q19? The stem and answer choices are different, but the answer is C.
https://7sage.com/lsat_explanations/lsat-63-section-3-question-19/

63.3.19 is about the conception of one's physical environment based on a single momentary perception.

runiggyrun

@"Dillon A. Wright" it's 63.1.19. I completely forgot to point that out....

Tina Cho

I'm still not sure about C....
Why do we have to compare DNAs of Home sapiens and Neanderthals?
So for example, Mother X, Kid Z, Father Y (not true father)...If we want to know whether X and Y were real parents, the Kid Z wants to check whether their DNA is similar to Y, not checking whether X and Y have similar DNA...If we know they have similar DNA, all what we will know will be that they may be related (such as sister/brother relationship)
Why do we have to know X and Y does not have significant similar DNA here to show X and Y did not...interbreed?

Stevie C

@"Tina Cho" said:
I'm still not sure about C....
Why do we have to compare DNAs of Home sapiens and Neanderthals?

Tina, I don't think your analogy (parents and a kid) is helpful.

This question is made easier by familiarity with the topic. So we have Neanderthals (40,000+ years ago) --> Early Homo Sapiens (thousands of years ago) --> Modern People (now). Neanderthals are extinct. Homo Sapiens are not extinct: we are all homo sapiens.

Conclusion: early Homo sapiens did not breed with neanderthals
Premise: DNA of modern people is very different from DNA of neanderthals, to the extent that they could not have interbred

Do you see the assumption? We're using evidence about today's humans to back up a claim about people who lived thousands of years ago. So, we're assuming that human DNA hasn't changed much since then.

Negate choice C to see why it's correct. If early human DNA was much more similar to Neanderthal DNA, then our argument falls apart. In that case, they could possibly have interbred.

steve-10

This question presumes some knowledge, perhaps more than it ought. It presumes the testee knows that homo sapiens is our (modern people's) species. It presumes that the testee knows that interbreeding will produce DNA similarities. It presumes that the testee knows that DNA can change across many generations. So:

If there had been interbreeding, then there would more DNA similarities between human (homo sapiens) ancestors and Neanderthals than we observe;
The differences we observe are not due to changes in human DNA since Neanderthals lived -- required assumption per (C);
Therefore there was not interbreeding.

Tina Cho

Hi, thank you for replying,

@"Stevie C" said:
So we have Neanderthals (40,000+ years ago) --> Early Homo Sapiens (thousands of years ago) --> Modern People (now).

Wait...so how can they interbreed if there is such a huge time blank (40,000yers and thousands of yrs) isn't it obvious they did not interbreed then?
How can they interbreed if they do not exist in the same time range? If they interbreed they will have similar DNA?? (If so then I think I understand why C is the answer though...)
The prehistoric Homo sapiens taked in stimulus and C are the same right? Or they are thinking prehistoric Home sapiens are descendants...?? sorry but I'm still confused...

Tina Cho

Thank you for your answer,

@"steve-10" said:
If there had been interbreeding, then there would more DNA similarities between human (homo sapiens) ancestors and Neanderthals

So...if they have interbred, they will have similar DNA??

Stevie C

@"Tina Cho" said:
Wait...so how can they interbreed if there is such a huge time blank (40,000yers and thousands of yrs) isn't it obvious they did not interbreed then?
How can they interbreed if they do not exist in the same time range? If they interbreed they will have similar DNA?? (If so then I think I understand why C is the answer though...)

Neanderthals and people (Homo sapiens) did coexist for a period of time.

Since the author is arguing that they didn't interbreed, "were both alive at same time" is not a necessary assumption here.

The reverse (were never alive at same time) would be a sufficient assumption: as you said, they couldn't have interbred if their time periods hadn't overlapped.

To answer your last question, I'm not 100% sure on the logical structure of this argument. I think it's saying [ (Very Different DNA) --> (Could Not Have Interbred) ] so in other words [ (They could have interbred) --> (DNA is similar) ] ... Once we introduce the idea that their DNA was similar, does this argument help us conclude anything? No. In the first one, sufficient is failed. In the contrapositive, the necessary is satisfied. Either way, we can't conclude anything.

Tina Cho

@"Stevie C" said:
Do you see the assumption? We're using evidence about today's humans to back up a claim about people who lived thousands of years ago. So, we're assuming that human DNA hasn't changed much since then.

Ahh...
After having thought about this question so many hours...(yes I did...)I think I finally got what you mean by this!
At first I was not sure why they have to compare DNA of prehistoric homo sapiens with that of N's, cuz I thought there is just no need to compare...I thought we only need to assume DNA of modern people and prehistoric homo sapiens are equivalent (due to the word switch as you raised) but since the premise uses this evidence "significantly different" to arrive the conclusion, prehistoric homo sapiens' DNA has to be also significantly different from N's...right? (no?
This is just another way of saying DNA of moden people and homo sapiens are so similar that we can use either of them to make a conclusion about the other right? (...no?)

Let me know if I understand what you said correctly, and if not could you correct my misunderstanding?
Thanks for the help!

Stevie C

@"Tina Cho" said:
This is just another way of saying DNA of moden people and homo sapiens are so similar that we can use either of them to make a conclusion about the other right? (...no?)

Let me know if I understand what you said correctly, and if not could you correct my misunderstanding?

To summarize, the conclusion is about prehistoric humans and Neanderthals. But the premise compares DNA of modern humans and Neanderthals. The argument is okay, as long as we assume that human DNA hasn't changed much since prehistoric times (C fills the gap).