Paleontologist: Scientists have used evidence about bone structure to

­ameya.satyawadi

It seems like option D is not connected to the conclusion. It has no relationship/effect on the argument that small genomes were not an evolutionary adaptation. 

Option A strenghtens the argument. If we take another look, the flying animals with small genomes evolved from their flightless ancestors, who did not need small genomes to conserve energy to fly-- since they did not fly. So the modern flying animals did not adopt the small genomes out of evolutionary necessity either. ­

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don't really understand this question. Human dinosaurs --- what is this in the question?

Human dinosaurs " are the recent flightless ancestors from which birds evolved.
MartyMurray KarishmaB
Can you please help on this question ?

Posted from my mobile device

Basically we need to prove that the small genomes in birds are not an evolutionary adaptation to conserve energy during flight.
It was small in case of their recent ancestors and that's why it is also small in them ( birds).
Option A states that this feature of small genome is present amongst other flying animals too ( other than birds ) and also in case of their flightless ancestors .
Since this same thing can be seen amongst other flying animals too ,
the conclusion gets strengthened that the evolutionary adaptation is not what is causing the small genomes. Small genomes are present in the birds because they were present amongst their ancestors . They ( the birds) simply inherited it just the way other flying animals did from their flightless ancestors.
MartyMurray Sir / KarishmaB maa'm , request you to check my reasoning.

Posted from my mobile device

 

­This part doesn't capture what choice (A) says:

The choice (A) says the following:

A. Species of flying animals other than birds typically have genomes no smaller than those of their most recent flightless ancestor species.

Notice that choice (A) does not say species other than birds have "this feature of small genome." Quite the contrary, it says that their genomes are "no smaller" than those of their ancestors. In other words, they may be quite large.

So, the point is that other flying animals do not have genomes that are smaller than those of flightless ancestors even thought they fly. This information indicates that animals that evolve to fly don't tend to evolve smaller genomes. That information indicates that birds have small genomes just because their ancestors did.

­Paleontologist: Scientists have used evidence about bone structure to infer that carnivorous dinosaurs like Trynnasauraus rex had genomes - sets of genetic information in their DNA - much smaller than those of most modern mammals. Modern birds have genomes about the same size as those of carnivorous dinosaurs, from which they evolved. Therefore, the hypothesis that small genomes in birds were an evolutionary adaptation functioning to conserve energy for flight is probably false.

The conclusion of the argument is the following:

the hypothesis that small genomes in birds were an evolutionary adaptation functioning to conserve energy for flight is probably false

The reasoning of the argument is basically the following. Birds evolved from dinosaurs that had small genomes. So, it's probable that the  reason birds have small genomes is not that they evolved small genomes to conserve energy but simply that they evolved from ancestors that had small genomes and thus ended up with small genomes.

Which of the following, if true, most strengthen the argument?

This is a Strengthen question, and the correct answer will somehow help to support or confirm the conclusion.

A. Species of flying animals other than birds typically have genomes no smaller than those of their most recent flightless ancestor species.

This choice is interesting.

If species of flying animals other than birds typically have genomes no smaller than those of their most recent flightless ancestor species, then what we see is that, when animals have evolved from being flightless to flying, their genomes haven't become smaller.

While that information doesn't prove that birds didn't evolve relatively small genomes to conserve energy for flight, it helps to support that conclusion.

After all, if these other animals didn't evolve smaller genomes as they evolved to flying, then it could be that relatively small genomes aren't very helpful for flying.

Therefore, maybe birds didn't evolve small genomes to help with flying. In that case, it's quite possible that birds' genomes are relatively small just because their ancestors' genomes were relatively small.

So, this choice helps to confirm that the conclusion of the argument is correct.

Keep.

B. Flying mammals such as bats have genomes about the same size as modern bird genomes.

This choice weakens the support for the conclusion.

After all, if flying mammals such as bats have genomes about the same size as modern bird genomes, then we have other examples of flying animals with relatively small genomes. The fact that other flying animals also have relatively small genomes tends to indicate that flying animals evolve to have small genomes for some purpose that they all share, which could be to conserve energy for flight.

By supporting the conclusion that flying animals evolve to have small genomes to conserve energy for flight, this choice weakens rather than strengthens the case for the conclusion of the argument.

Eliminate.

C. Species with small genomes typically use energy much more efficienly than do closely related species with larger genomes.

If anything, this choice weakens the support for the conclusion.

After all, if this choice is true, then it make sense that birds would have evolved relatively small genomes to conserve energy for flight.

Of course, by indicating that that makes sense, this choice weighs against the conciusion of the argument.

Eliminate.

D. Many animal species that lived in the period as Tyrannosaurus rex but were not ancestors of modern birds, also had relatively small genomes.

This information about other animal species doesn't indicate whether birds evolved relatively small genomes to conserve energy or just retained small genomes from their ancestors.

After all, these other animals have no clear relationship with birds. They just happened to have small genomes.

Eliminate.

E. At least some flightless species that evolved from carnivorous dinosaurs and were ancestors to modern bird species had much larger genomes than modern birds have. 

If anything, this choice slightly weakens the argument.

After all, if this choice is true, then flightless ancestors of some birds had larger genomes than those birds have.

That information indicates that some birds evolved to have genomes that are smaller than their flightless ancestors had, which in turn tends to indicate that those birds have relatively small genomes because they fly, and thus benefit from conserving energy, whereas their ancestors didn't fly.

That train of logic goes against the conclusion of the argument.

Eliminate.

Correct answer: A

Thank you marty !! 

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Hypothesis: Genome sizes shrank to develop the ability to fly (by developing the ability to conserving energy).
Author says hypothesis is not true. We have to strengthen the author's statement.
So we need to show that Small genomes are not required for / Not related to flying ability OR genome sizes did not shrink while the species developed ability to fly.

A) Species of flying animals other than birds typically have genomes no smaller than those of their most recent flightless ancestor species.

Genome size of Flying species greater than or equal to flightless species. Which supports the main conclusion that small genomes are not required for / Not related to flying. Genome sizes have remained constant or increased during the development of ability to fly in the species.

B) Flying mammals such as bats have genomes about the same size as modern bird genomes.
Doesn’t tell anything about the logic/conclusion.

C) Species with small genomes typically use energy much more efficiently than do closely related species with larger genomes.
Small genomes are co-related to energy conservation. Weakness the argument.

D) Many animal species that lived in the same period as Tyrannosaurus rex but were not ancestors of modern birds also had relatively small genomes.
Out of scope. Not linked to modern birds.

E) At least some flightless species that evolved from carnivorous dinosaurs and were ancestors to modern bird species had much larger genomes than modern birds have.
Weakens the argument. Flying species had smaller genomes than those of flightless species.­

The argument is tricky because it plays on one’s visual interpretation of the information. It uses a prehistoric large animal, such as a dinosaur, to lead the reader down the wrong path by incorrectly associating “structure” with “size”—a common trick that the GMAT often employs. However, the term “structure” does not tell us anything about size. The birds might have a similar bone structure to dinosaurs in terms of form, but not necessarily in size.

Letting go of this misleading association helps in understanding the argument better. It also helps to recognize that the genomes in birds are not actually small; they are quite large if they are comparable in size to those of dinosaurs. From this perspective, it’s easier to see that birds have relatively large genomes, which means the conclusion that these genomes are small as an adaptation to conserve energy for flight cannot be correct. To strengthen the conclusion, we need to find similar cases where the size of genomes has no merit on the flying ability. Choice A does that.­