Logical Reasoning

PT122 · S1 · Q10 In an experiment, scientists changed

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In an experiment, scientists changed a single gene in cloned flies of a certain species.

Conclusion (Thus)

Scientists have shown that flies of this species lacking UV vision must have some damage to this gene.

Evidence

In an experiment they changed this single gene in cloned flies and the clones lacked the eye cells that give flies UV vision (while the cloned flies with otherwise identical genes still had normal vision).

Evaluate

At first it may seem hard to see the wiggle room in this argument.

Given that ... changing this one single gene resulted in flies without UV vision, How can we argue that ... flies of this species lacking UV vision must have damage to this gene?

The flaw would actually be similar to this argument:

The study shows that a certain factor is sufficient to bring about a certain effect, but the conclusion is acting like that factor is necessary to bring about that effect. In doing so, it's failing to consider other possible reasons why that effect might be observed.

The $50,000 argument was failing to consider that people might sometimes buy new cars, even though they didn't get $50k in some experiment. Maybe they just got a raise or their old car broke down.

Similarly, this argument is failing to consider that flies might sometimes lack UV vision even though they had no damage to that specific gene. Maybe they swallowed some toxin that ruined their UV vision. Maybe something scratched the surface of their eyes and ruined the UV vision

Goal

Look for an answer either naming the Linking move the argument makes:

if changing this gene → any fly with no UV has means no UV damage to this gene

Or, more probably, look for a Defender answer that is ruling out a possible objection, like .

10.

Which one of the following is an assumption required by the argument?

The relationship between genes and
Too Strong: well understood
If we negate this and say that the relationship is only partially understood, does that weaken the argument? Not really. We definitely understand that changing this single gene in this species of fly causes there to be no UV vision, because we have a perfect control group (cloned sibling with unaltered, otherwise identical genes) who didn't lose their UV vision. For the sake of this argument, that's all the author needs to assume we understand well.
3% picked this
Correct
No other gene in the
Why this is right
This has the lovable ruling-out "not / no" that is in so many correct Necessary Assumption answers. We think of this style of wording as an invitation to use the Negation Test. If we negate this and say that "there are other genes for this species of fly that are required for the formation of the UV cells", does that weaken? Yes! It points to an alternate way that a fly of this species could lose its UV vision. Let's say that all the genes from gene 80 to gene 85 are required for the formation of UV cells. Researchers found that when they changed gene 82, the fly no longer had UV vision, and the author concludes that any time we see a fly of this species lacking UV vision, it must have some damage to gene 82. But the negation of this answer is saying that changing gene 80, or 81, or 83 / 84 / 85 would have also caused the fly to lose UV cells. So if we see a fly of this species that lacks UV vision, we can't be sure it has a damaged gene 82. It might have a damaged gene 80 instead. We didn't know what specific alternate explanation they would give us, but we anticipated that the way to hurt this argument was to say there could be some other way that a fly of this species would end up with no UV vision, and thus we can't act like "damage to this gene" is the only possible cause.
Skill tested: Necessary Assumption · how this choice captures the argument's function is the move to repeat next time.
74% picked this
Ultraviolet vision is a trait
Too Strong: all
The author doesn't need to assume that UV is a trait found in any other species of fly besides the one the argument is about. She certainly doesn't need to assume it's present in 100% of flies. Would it change her argument if we negated this and said, "Hey, author -- UV vision is only found in 99% of flies"? Of course not. Her conclusion isn't about flies in general; it's only about "flies of this species".
8% picked this
The gene change had no
Too Strong: no other effects
This also has the lovable ruling-out "not / no" format, so let's negate. Does it hurt the argument if we say, "Hey, author -- the gene change also gave the flies weird smelling breath / or, it changed the rate at which their wings flap / or, it made them more susceptible to fly acne." The author doesn't care. Her logic is only concerned with the fact that we know changing this gene did take away the UV vision. Her conclusion is trying to reason backwards from a fly with no UV vision. Other effects wouldn't have any impact on the conversation.
14% picked this
Ultraviolet vision is an environmentally
Weakens
The author needs to assume that UV vision is not an environmentally influenced trait. If it is environmentally influenced trait, then there could be alternate explanations for why a fly of this species lacks UV vision. We might look at such a fly and think, "Maybe it had damage to gene 82, like in the experiment. But ... maybe it lost its UV vision from some environmental factor, like eating a poisonous toxin."
2% picked this

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