Raman109
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.
Which of the following, if true, most strengthen the argument?
A. Species of flying animals other than birds typically have genomes no smaller than those of their most recent flightless ancestor species.
B. Flying mammals such as bats have genomes about the same size as modern bird genomes.
C. Species with small genomes typically use energy much more efficienly than do closely related species with larger genomes.
D. Many animal species that lived in the period as Tyrannosaurus rex but were not ancestors of modern birds, also had relatively small genomes.
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.
Premises: C dinosaurs like T rex (no flight) had much smaller genomes than those of most modern mammals.
Modern birds have genomes about the same size as those of C dinosaurs, from which they evolved.
Conclusion: Hypothesis that small genomes in birds were an evolutionary adaptation functioning to conserve energy for flight is probably false.
The author says that birds evolved from C dinos and they have the same small genomes as those of C dinos. So looks like they have inherited small genomes were C dinos. These small genomes are not an adaptation in birds to conserve energy for flight.
We need to strengthen this so we are looking for something that tells us - yes, birds just inherited the small genomes. They did not evolve to have small genomes to conserve energy for flight. So look for this - "Flight has nothing to do with small genomes".
A. Species of flying animals other than birds typically have genomes no smaller than those of their most recent flightless ancestor species.
Flying animal genomes are no smaller than those of their non flying ancestors. So it looks like birds and animals don't evolve to have small genomes to conserve energy for flight. It they were evolving to have small genomes, then the genomes of flying animals would be expected to be smaller than those of their non flying ancestors. Hence this is further evidence supporting the author's conclusion. Correct.
B. Flying mammals such as bats have genomes about the same size as modern bird genomes.
Flying mammals genomes are same as modern bird genomes. Both fly. Both have same size genomes. No comparison between non flying animals and flying animals/birds.
C. Species with small genomes typically use energy much more efficienly than do closely related species with larger genomes.
Nothing related to flight given here. Do birds evolve to have smaller genomes to conserve energy for flight? Doesn't say. Note that even if it was given that it helps in flight, this would strengthen the hypothesis, not the author's argument. It would weaken the author's argument. We are looking for "Flight has nothing to do with small genomes". This option says that small genomes use less energy (so actually may be useful during flight). Hence it would go the opposite way.
Typical GMAT trap!
D. Many animal species that lived in the period as Tyrannosaurus rex but were not ancestors of modern birds, also had relatively small genomes.
Just says that small genomes were common at that time. No connection to flight.
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.
Again, it somewhat weakens our argument. We are looking for "Flight has nothing to do with small genomes". But this says that there are some bird ancestors with much larger genomes. Then it could be possible that birds evolved to have smaller genomes to conserve energy for flight. Goes against what we are looking for.
Answer (A)Some discussions on strengthen questions:
https://youtu.be/mB8bm_a4GNkhttps://youtu.be/uPdDYbYpXuIhttps://youtu.be/9o3y4Hz16es