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#26313
Complete Question Explanation

Weaken—CE. The correct answer choice is (D)

The argument states that identical twins are virtually the same genetically. The twins in the studies are genetically identical, yet are separated at birth and brought up in vastly different environments. Many of their inclinations in life are still identical, however. This suggests that the one constant between the twins, genetics, must be the cause of those inclinations:
  • Cause ..... ..... ..... Effect

    Genes ..... :arrow: ..... Similar inclinations
Like most causal arguments on the LSAT, this argument is inherently weak. There could be many alternate explanations for why these twins experience similar inclinations later in life that do not involve genetics.

Answer Choice (A): The radical changes in lifestyle in this answer choice are not necessarily changes to the same inclinations discussed in the stimulus. That would make this answer choice irrelevant to the argument. On the other hand, even if we assume that the radical changes here are to the same inclinations discussed in the stimulus, it is still possible that the separated identical twins experience these radical changes in a similar fashion. Since the twins are once again displaying similar characteristics, this would actually strengthen the argument by making it more likely that genetics is the cause of these characteristics. In either case, this answer choice fails to weaken the argument.

Answer Choice (B): The conclusion in the stimulus is that many of our inclinations must be genetic in origin, not that all of our inclinations are genetic in origin. This conclusion leaves open the possibility that while many inclinations are genetic in origin, some inclinations may not be genetic in origin. So, the fact that these twins have some differences is irrelevant to the argument.

Answer Choice (C): This answer choice is also irrelevant to the argument. Even though scientists cannot link the inclinations to any specific gene, these inclinations could still be the result of a genetic cause that has yet to be identified.

Answer Choice (D): This is the correct answer choice. In this answer choice, the twins who grow up together are still identical and so the genetic cause is still present. However, these twins show different inclinations and so the effect from the stimulus is not present. Any answer choice that presents a situation where the cause occurs yet the effect fails to occur weakens a causal argument.

Answer Choice (E): This answer choice strengthens the argument. If twins are not identical, then they don’t have the same genes and the cause is not present. Also, the fact that they also develop different beliefs, tastes, and careers suggests that they have different inclinations and so the effect from the stimulus is also not present. Any answer choice that shows a situation where the cause does not happen and the effect also does not happen strengthens a causal argument.
 jenna_d
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#38430
It is still unclear to me in this question how the answer weakens the argument. The conclusion is: Thus, many of our inclinations must be genetic in origin, and not subject to environment influence. So in D, the inclination is to develop differences and the environmental condition is growing up together? Therefore, it goes against the argument because they are in fact subject to environmental influences? Thanks!
 AthenaDalton
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#38476
Hi Jenna,

Yes, I think you described the argument well.

The psychologist is arguing that genetics, and not environmental factors, is the cause of many traits based on the examples of identical twins raised separately. If the twins are subject to drastically different environments yet still end up developing the same traits, those traits must stem from genetics.

Answer choice (D) counters this with the anecdote of identical twins raised together who nonetheless develop different traits. In answer choice (D), the twins have identical genetics and identical environments, yet don't develop identical traits. If genetics really were the controlling factor, identical twins raised together should develop identical traits.

I hope that helps clear things up. Good luck studying!

Athena Dalton

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