Logical Reasoning

PT146 · S2 · Q11 Human skin gives off an array

A free, expert breakdown of this official LSAT Logical Reasoning question.

Save & drill this skill — build targeted practice sets from questions like this one
Video walkthroughs — watch every question solved step by step
81 official LSATs — as questions, timed sections & full-length tests

Human skin gives off an array of gaseous substances, including carbon dioxide and lactic acid, both of which attract mosquitoes.

Conclusion

Some gas, besides carbon dioxide and lactic acid, is given off my the human arm is attractive to mosquitoes.

Evidence

The human arm gives off an array of gases. Two of those gases are carbon dioxide and lactic acid. Each of those gases attracts mosquitoes.

But if you put a mosquito in complete darkness, and you offer it just carbon dioxide, just lactic acid, the combo of CO2 and lactic acid, or a human arm, the mosquito picks the human arm.

Evaluate

Since the author is trying to Solve a Causal Mystery in her conclusion, we can use the Curious Fact / Explanation template.

Curious Fact Why do mosquitoes pick a bare human arm over CO2, lactic acid, or the combo of the two?

Author's Explanation The human arm gives off some other gas that is also attractive to mosquitoes.

Correct answers always deal with one of these two pressure points: 1. Alternate Explanations for the Curious Fact 2. the Plausibility of the Author's Explanation

Since this is Necessary Assumption, a correct answer will either - rule out an Alternate Explanation for why mosquitoes prefer human arms, or - provide something that's essential to the plausibility of the Author's Explanation.

For example - mosquitoes are not attracted to human arms because of the smell of blood inside. or - mosquitoes are attracted to more than two types of gases (essential for the author's explanation to be true)

Goal

Look for an answer ruling out an Alternate Explanation for why mosquitoes prefer a human arm to CO2/lactic acid by themselves, or for an answer saying something that would have to be true in order for some third gas to be coming out of a human arm and adding yet another attractive layer for mosquitoes.

11.

The reasoning in the argument requires which one of the following assumptions?

Mosquitoes do not communicate with
Out of Scope / Irrelevant
When answer choices on Necessary Assumption use "not" to rule out an idea, that's very attractive to us. We should negate it to see whether it weakens. If "mosquitoes can communicate with one another" would that weaken the argument? Is that a different explanation for why they like human arms more than just those two gases? No. If mosquitoes can communicate with one another, does that disrupt the author's storyline that mosquitoes like at least a third gas that comes out of human skin? Nope.
1% picked this
Correct
Mosquitoes are not attracted to
Why this is right
When answer choices on Necessary Assumption use "not" to rule out an idea, that's very attractive to us. We should negate it to see whether it weakens. If "mosquitoes are attracted to humans by body heat" would that weaken the argument? Yes! That would be a different explanation for why they like human arms more than just those two gases they like. When we negate this answer, it's letting us say, "in the experiment, the mosquitoes liked the human arm more than the CO2 / lactic acid because they were attracted to the body heat coming off the human arm, not because there was some other gas in addition to CO2 / lactic acid that the mosquitoes liked".
Skill tested: Necessary Assumption · how this choice captures the argument's function is the move to repeat next time.
74% picked this
Human skin gives off gaseous
Irrelevant Comparison
The author wasn't assuming that human skin had any sort of variation in how much gas it gave off in different situations. This conversation is seemingly assuming that human skin is constantly in a state of giving off an array of gases, and the author makes no distinction about different time periods.
2% picked this
Mosquitoes are not more successful
Irrelevant Comparison
When answer choices on Necessary Assumption use "not" to rule out an idea, that's very attractive to us. We should negate it to see whether it weakens. If "mosquitoes are more successful finding a bare arm in darkness" would that weaken the argument? Is that a different explanation for why they like human arms more than just those two gases? No. Being better at finding an arm when the lights are out doesn't explain why they want to go to the arm in the first place. If mosquitoes are better at finding arms in the dark, does that disrupt the author's storyline that mosquitoes like at least a third gas that comes out of human skin? Nope. The third gas is coming out of the arm whether it's light/dark, whether it's easier or harder for a mosquito to find a human arm.
15% picked this
Human skin never gives off
Too Strong: never
The author doesn't have to assume that never-ever-ever does human skin ever give off any gaseous substance that repels mosquitoes. Maybe right when we die, our skin expels a nasty death gas that mosquitoes don't like. That wouldn't change the argument in the slightest.
8% picked this

Continue the review in LSAT Lab

Save this question, watch the video walkthrough, and drill similar questions in your LSAT Lab account.

Save and practice this skill

LSAT Lab

Turn this review into a targeted study plan.

Save this question, drill more like it, watch the video walkthrough, and track your progress in your LSAT Lab account.

Start practicing free