Logical Reasoning

PT137 · S4 · Q6 Columnist: Contrary to what many people

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Columnist: Contrary to what many people believe, the number of species on Earth is probably not dwindling.

Conclusion

The number of species on Earth is probably not dwindling (i.e. the number of species is probably holding steady or going up)

Evidence

About as many species will go extinct this year as went extinct in 1970. And the number of new species will emerge this year will be about the same as the per/year average of the last few hundred centuries.

Evaluate

The truth value of this conclusion is purely mathematical. Every year we gain species and lose species. We just need to know if right now we're at "net gain" or "net loss".

So how do we evaluate if we're gaining more species than we're losing or vice versa.

We're gaining whatever the average # of new species / year has been for the past few centuries. We're losing whatever number of species went extinct in 1970.

Goal

Since the author is assuming we're gaining more than we're losing, she must be assuming this comparison:

Average number of number of new species per year → species lost in (over the last few 1970 centuries)

We could weaken the argument by making it seem like 1970 was a year with a "net loss", where the number of species lost outweighed the number of species gained.

No matter what, our answer needs to help us argue that the number of species on Earth is dwindling.

6.

Which one of the following, if true, most weakens the columnist's argument?

  1. Correct

    In 1970 fewer new species

    Why this is right

    The author's argument is, "Why are these people saying the Earth is losing species? We're doing fiiiiine. We're doing just as good today as we were in 1970!" This answer choice: Hey, bro? In 1970, we were losing species. 1970 was a year with a "net loss" (we lost more than we gained). Our current year has the same rate of gain and same rate of loss as 1970, so this answer pretty much establishes that this year will also be a net loss. Thus, the number of species on Earth is dwindling, at least this year.

    Skill tested: Weaken · how this choice captures the argument's function is the move to repeat next time.

    69% picked this

  2. The regions of the world

    Unclear Impact

    By focusing on a small part of Earth (this answer is only talking about outlier regions, the ones with the highest rate of speciation and the highest rate of extinctions), it's only going to give us part of the picture we need. For example, if an answer said, "The number of species that will go extinct in Canada this year is less than the number of new species that will be created", that wouldn't really help us assess the overall debate of the conclusion, which is about net gain/loss of species on the entire Earth. Even more importantly than "certain regions vs. entire Earth" is the fact that this answer doesn't even tell us within these regions whether it's a net gain or net loss of species. We're just told that in these regions they gain more species than anywhere and lose more species than anywhere, but we don't know whether they gain more than they lose or vice versa.

    7% picked this

  3. The vast majority of the

    Irrelevant

    We're told that species are always going extinct and being created. It's a pretty foregone conclusion that most species that have ever existed are now extinct. Earth has been creating (and extinguishing) forms of life for like 3 billion years. So the number of species currently alive vs. the number of species that have gone extinct over 3 billion years doesn't seem like a fair fight. The author is just arguing that our current rate of speciation eclipses our current rate of extinction (a net gain of species each year).

    13% picked this

  4. There is no more concern

    Strengthens, if anything

    This makes it seem like nowadays doesn't seem any worse to people than 1970 did, which would help the author argue, "Relax ... we're not falling off a cliff. Look we're no worse off than 1970." Had we said, "yes, author, we're losing species at the same rate as 1970, but there is much more concern now than there was in 1970 about losing species", that would have helped us weaken a little, but given that it's opinion not fact, it doesn't really have much impact.

    1% picked this

  5. Scientists are now better able

    Irrelevant

    Having a better ability to identify species on the brink of extinction might be relevant to how likely we are to save the species going extinct, but it doesn't do anything to help us judge the math of how many species went extinct this year vs. how many new species emerged this year.

    9% picked this

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