Even the earliest known species of land animals, known from fossils dating from the late Silurian period, 400 million...

Billy on July 26, 2019

Need clarity..

I'm a bit lost here. Can you help? I think I understand the stimulus, but I'm unclear why A is the answer...

2 Replies

Irina on July 28, 2019


The question asks us to identify an assumption necessary for the argument to follow logically.

Let's briefly look at the argument.

Even the earliest known species of land animals show highly evolved adaptations to life on land. Since neither aquatic nor amphibious animals exhibit these adaptations, early species of land animals must have evolved very rapidly after leaving an aquatic environment.

There are two implied assumptions here:
(1) these early land animals have evolved from aquatic or amphibious animals, otherwise, the fact that neither aquatic nor amphibious animals exhibit these adaptations would be irrelevant;
(2) these land animal fossils are from a time period that is relatively close to the time period when early land animals originated, else we cannot conclude that the land animals evolved rapidly if there are thousands of years between these two time periods.

The correct answer choice (A) reflects the second assumption arguing that there is no significant time gap between known fossils of early animals and the first emergence of land animals.

Does this make sense? Let me know if you have any other questions.

Billy on July 28, 2019

Yes, this helps a lot. Thank you!