#21 - Even the earliest known species of land animals, known

[heartofsunshine]

Hi there,

I am confused on the correct answer choice here. Essentially this argument is saying that the known species of land animals from fossils show highly evolved adaptations to life on land. And since aquatic animals don't shows these adaptations, land animals evolved rapidly after leaving an aquatic environment. (conclusion in bold)

One paraphrase assumption that come to mind: land animals must originated from aquatic settings.

I guess maybe I am misunderstanding what answer choice A is saying.. My answers were between A and E but neither really seemed like a good choice..can you elaborate on why A is correct?

[Jeremy Press]

Hi heartofsunshine,

I want to adjust your understanding of the stimulus just slightly (though I think for practical purposes you have a good grasp). Half of what you bolded is actually part of the premises. "Since" is a premise indicator, and everything in the sentence you bolded before the comma is actually premise. So the conclusion is just the last portion of the last sentence. From the stimulus, this portion is the conclusion: "early species of land animals must have evolved very rapidly after leaving an aquatic environment."

You have a prephrase that would certainly work for this question. But you have to be careful on Assumption questions (and on all Family 2 and 3 questions) that you don't "lock yourself in" to one very specific prephrase. Every argument has numerous possible assumptions, and there's always a possibility that the test-makers choose an assumption that doesn't fit your specific prephrase.

Focus instead on the problem that's exhibited by this argument. What do the premises consist of? Only the "known fossils" of the "earliest known" species of land animals. How do we know that our knowledge is complete? We don't. There might be other fossils (and thus even earlier instances of land animals) that we don't know about. If that were the case, we wouldn't necessarily have to say that land animals evolved very quickly after leaving an aquatic environment. If there were earlier land animals we don't know about, those animals could've taken some time to evolve, and the species from the fossils we know about wouldn't have had to evolve very quickly at all.

That's a major problem for this argument, so the author of the argument has to assume that such a scenario did not occur. In other words, the author of the argument has to assume the fossils we have are fossils of animals that did indeed come from the aquatic environment and then extremely quickly evolve their land adaptations. Answer choice A says essentially that: the fossils that we know about did indeed come directly from (i.e. "lived relatively soon after") the emergence of such animals from the aquatic environment.

I hope this helps!

Jeremy