Logical Reasoning

PT137 · S3 · Q13 Psychologist: Identical twins

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Psychologist: Identical twins are virtually the same genetically.

Conclusion

Many of our inclinations are genetically caused and not affected by environmental influence.

Evidence

Identical twins, who have the same genes, tends to be similarly inclined when it comes to ethics, fashion, and career choice, even when they've been brought up in vastly different environments.

Evaluation

The author looks at these cases of different upbringings (environment) but similar ethics/fashion/career ambitions and attributes that sameness to the similar genes.

If we were trying to argue the Anti-Conclusion, we'd have to think,

Goal

We could look for an alternate explanation (non-genetic) for why these identical twins raised in different environments ended up with similar inclinations, or we can look for an answer that suggests that these inclinations aren't genetic, or are affected by environment.

13.

Which one of the following, if true, would most weaken the psychologist's argument?

  1. Many people, including identical twins,

    No Impact

    It might feel like "undergoing a radical change in lifestyle" is evidence that something environmental, not genetic, is going on. That's probably fair, but the author wasn't saying that all of our lifestyle traits are genetic. He's only arguing that some of our lifestyle inclinations, like ethics / fashion / job seem to be genetic. There can be genetically-induced changes in lifestyle too: puberty and menopause or an adult-onset cancer can all make pretty radical lifestyle changes happen.

    4% picked this

  2. While some studies of identical

    Too Weak

    The author's conclusion is only saying that "many inclinations" are genetically, not environmentally, determined. It doesn't hurt her argument if there are a few differences between identical twins.

    4% picked this

  3. Scientists are far from being

    Too Weak

    True, it would strengthen the argument if we knew that scientists had already linked specific genes to many inclinations. But the fact that they haven't yet and are far from doing so isn't evidence that those links don't exist. Or at least, it's very, very weak evidence that those links don't exist. One of the famous flaws is Unproven vs. Proven False, in which we make this very complain: just because scientists haven't proven there is a genetic basis to inclinations doesn't prove that there isn't a genetic basis to inclinations.

    14% picked this

  4. Correct

    Identical twins who grow up

    Why this is right

    This presents a Cause, No Effect weakener to the author's causal claim. The author thinks that in the identical twins raised in different environments, their common genes caused them to have similar ethics / fashion / career choice. But here are some data points (and many of them, because it's "tend to") in which we have common genes, but different ethics / fashion / career choice. This suggests that those inclinations are not genetically determined, or if they're genetically influenced they are still subject to environmental influence such as the intra-family pressure to be into different stuff than your sibling is.

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

    74% picked this

  5. Twins who are not identical

    Strengthens

    This gives the author a No Cause, No Effect strengthener. He thinks that having the same genes leads to similar beliefs / tastes / careers, so examples of different genes leading to different beliefs / tastes / careers corroborates his thinking. Non-identical twins, i.e. fraternal twins, are still genetically similar (because they're siblings) but they're as similar as any pair of siblings that aren't twins.

    4% picked this

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