Q4

[tzyc]

How does C undermine the author's argument?
I thought it actually stregthens the argument because in the passage it says the brain would have to be substantially bigger if it had to carry all the information...
Is it because since this is hypothesis, it's the reverse in reality (so the brain is not bigger) and C shows it's not true?

Thank you

[tommywallach]

Hey Strawberry,

So you're absolutely right that the explanation cited here is that "[The canary's] brain would have to be substantially larger and heavier than might be feasible for flying if it had to carry all the brain cells needed to process and retain all the information gathered over a lifetime."

(A) This would strengthen the argument, because a shorter life span would mean the brain wouldn't retain so much information, and thus wouldn't get any heavier. This means there'd be no need to lose and then replace neurons.

(B) This would strengthen the argument by providing more data points.

(C) CORRECT. This undermines the point, because if it's possible to survive/thrive with an even heavier brain, then it doesn't make sense that the canary would need to shed and then rebuild neurons in order to fly effectively.

(D) This would actually strengthen the argument a tiny bit, implying that the size of the brain is related to how strong a bird needs to be in order to carry that weight.

(E) This doesn't relate to the flying/weight at all. We already know that brain size is correlated to song vocabulary.

Hope that helps!

-t

[JacquelineP303]

I am having some difficulty distinguishing between C and D. If C weakens because it shows that birds can in fact fly with heavier brains, and therefore, destroying neurons is not necessary for flight, then wouldn't D also weaken since we know that a larger-than-average repertoire means a larger-than-average brain? Also, how do we know that the birds in C also do not undergo neurogenesis (they may have substantially heavier brains than canaries, but are they too heavy for flight?)?

My thought process is that D would be incorrect, i.e. not weakening the hypothesis, because from the answer choice, we do not know that these canaries with larger-than-average repertoire fly with heavier brains, we just know that they have heavier-than-average brains because of their larger-than-average repertoire. When their neurons die in the summer/fall, they may still have heavier-than-average brains, but they can compensate with their stronger muscles. This answer would not weaken the hypothesis because does not show that these birds can fly with heavier brains, whereas C does.

[ohthatpatrick]

Where is "the explanation" in the third paragraph?

in line 40, we see "a possible explanation".

What are we trying to explain?
Why does the canary's brain seem to have this seasonal cycle of killing off the brain cells for last year's song and then growing new neurons to learn the next song.

Explanation?
If the canary needs to learn that many songs in its lifetime, which is actually a pretty long life time, then its brain size would have to be big in order to have the neurons necessary to have that big a hard drive. Since a heavy brain works against the ability to fly, evolution may have favored this cycle of "dump last year's brain cells, grow new ones for this year".

We could undermine this explanation by
- suggesting a different reason why the canary has this cycle of dump + regrow

- decrease the plausibility that concerns about brain size and overly heavy flying weight are the reason

(C) decreases the plausibility of the idea that brain size / flying weight is the limiting factor that causes the cycle of dump + regrow. After all, if other "airborne" (flying) birds with same body size can handle bigger brains, then it's less plausible to say "the canary wouldn't be able to fly with a heavier brain, so its brain needs to do this cycle of dump + regrow".

(D) This INCREASES the plausibility of the author's story, because it sounds like knowing more songs may have meant heavier brain, which is why these canaries have better flying muscles.

Hope this helps.