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Credit: Segal, Nancy L., Jamie L. Graham, and Ulrich Ettinger. "Unrelated look-alikes: Replicated study of personality similarity and qualitative findings on social relatedness." Personality and Individual Differences 55.2 (2013): 169-174.

Credit: Segal, Nancy L., Jamie L. Graham, and Ulrich Ettinger. “Unrelated look-alikes: Replicated study of personality similarity and qualitative findings on social relatedness.” Personality and Individual Differences 55.2 (2013): 169-174.

The New York Times summarizes some new research in behavior and personality, Holding a Mirror to Their Natures: Looking at Twin Personality Through Look-alikes:

As she expected, the unrelated look-alikes showed little similarity in either personality or self-esteem. By contrast, twins — especially identical twins — score similarly on both scales, suggesting that the likeness is largely because of genetics. Her results were published in the journal Personality and Individual Differences.

For a second study, she teamed with a skeptic, Ulrich Ettinger, a psychologist at the University of Bonn in Germany who had heard about the look-alike project during a postdoctorate at the University of Montreal.

“I thought that if two people looked alike, they would have similar personality traits because people would treat them the same,” he said. “For example, I thought men who looked alike and were tall and handsome would probably be extroverts.”

Their analysis was consistent with the findings of Dr. Segal’s first study: Personality traits do not appear to be influenced by the way people are treated because of appearance. Moreover, they found, there appears to be no special bond between look-alikes.

Segal, Nancy L., Jamie L. Graham, and Ulrich Ettinger. "Unrelated look-alikes: Replicated study of personality similarity and qualitative findings on social relatedness." Personality and Individual Differences 55.2 (2013): 169-174.

Segal, Nancy L., Jamie L. Graham, and Ulrich Ettinger. “Unrelated look-alikes: Replicated study of personality similarity and qualitative findings on social relatedness.” Personality and Individual Differences 55.2 (2013): 169-174.

The original study, Unrelated look-alikes: Replicated study of personality similarity and qualitative findings on social relatedness, is quite modest in scope. You can see the sample sizes are not large in the table to the left. With that said, I think this is adding to a growing body of results that validate the soundness of the original work on twins in behavior genetics. For many reasons this research program has come under sharp critiques over the past 50 years, but it seems to me that the big picture findings NoTwoAlike of modest heritabilities for most behavioral phenotypes is holding up. For a complementary tack I suggest Whole genome approaches to quantitative genetics, which uses different methods to explore some of the same class of
traits. Relying on the body of twin research alone as a foundation might be a shaky basis for conjecture, but now this area is going multi-disciplinary,
allowing for a stool with multiple legs. Of course all it is doing is confirming modest heritabilities for behavioral phenotypes. But one needs to remember that a lot of the environmental component is not amenable to control, whether by parents or society (i.e., it is “non-shared environment”).

God does play dice.

 
• Category: Science • Tags: Behavior Genetics 
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  1. […] Khan, in No two look-alikes, points out this New York Times article on examining the genetic component in twin behavior by […]

  2. “God does play dice.”

    This could serve as the inspiration for a whole series of publications (as part of trying to maximize the number of pubs per idea) for the next round of the multi-disciplinary approach:

    The quantum mechanics of behavioural genetics
    The quantum mechanics of quantitative genetics
    The quantum mechanics of behavioral phenotypes
    The quantum mechanics of phenotypical genetics

    Perhaps these would be better used as journal titles rather than article titles.

    RK: toss me some buzzwords, and I’ll use scigen (http://pdos.csail.mit.edu/scigen/) to help write some articles.

  3. I’m sorry, but the “if two people look alike they’ll be treated the same” theory is poorly thought out and deeply flawed. Two people from similar backgrounds who don’t look alike are probably more likely to share traits than people who do look alike but have completely different backgrounds.

  4. Anonymous • Disclaimer says:

    “First Law: All human behavioural traits are heritable.
    Second Law: The effect of being raised in the same family is smaller than the effect of the genes.
    Third Law: A substantial portion of the variation in complex human behavioural traits is not accounted for by the effects of genes or families.”

    – Turkheimer, E. (2000). Three laws of behavior genetics and what they mean.

    PDF: http://www.faculty.umb.edu/pjt/epi/turkheimer00.pdf

    “There is now a large body of evidence that supports the conclusion that individual differences in most, if not all, reliably measured psychological traits, normal and abnormal, are substantively influenced by genetic factors. This fact has important implications for research and theory building in psychology, as evidence of genetic influence unleashes a cascade of questions regarding the sources of variance in such traits. A brief list of those questions is provided, and representative findings regarding genetic and environmental influences are presented for the domains of personality, intelligence, psychological interests, psychiatric illnesses, and social attitudes. These findings are consistent with those reported for the traits of other species and for many human physical traits, suggesting that they may represent a general biological phenomenon.”

    – Bouchard, T. J. (2004). Genetic Influence on Human Psychological Traits: A Survey
    PDF: http://www.psy.miami.edu/faculty/dmessinger/c_c/rsrcs/rdgs/temperament/bouchard.04.curdir.pdf

    ..if anyone here hasn’t seen these.

  5. I’d have expected lookalikes to have somewhat similar personalities not because people treat them alike, but because of traits which influence both personality and appearance. For example, testosterone levels. But it seems that effect isn’t as strong as I thought.

  6. I have been pondering this since you posted it. If two people look alike, then obviously they ARE related, at least to some degree. I mean, nobody is ever going to walk up to me and say “Hey! You look just like Razib Khan!”, although I would take it as a compliment.

    So, if you accept that genes are partly responsible for behavior (and I do), this lack of correlation has to be explained. What I’m thinking on is that a big difference between closely related people and their look-alike cousins in the broader gene pool is that they share more identical blocks of genes, as opposed to individual genes. The differences in behavior might be a result of non-additive effects.

    I dunno. I am still thinking this through, but it appears to be a deep problem

  7. @6

    I noted this apparent paradox too. I think that the way that it resolves itself is that one doesn’t have to be too distant a relative to have a probability distribution of personality trait values that is indistinguishable in practice from a person chosen at random from the same general gene pool.

    My third or fourth cousins are not much more genetically similar to me than any other person whose ancestors are European Lutherans, and in particular, not so much more genetically similar that it would produce a statistically significant effect in a phenotype like personality that we can’t measure very precisely, for any practical sample size.

    Given this reality, while appearance similarity is probably going to get you to the same general gene pool, this will translate into genetic similarities in personality only to the extent that there are genetic differences in personality distributions between one gene pool (e.g. European Lutherans) and another (e.g. East Asians, or West African non-pygmies). These differences almost certainly exist in a Platonic ideal world where we knew exactly which genotypes corresponded to which personality phenotypes. But, in the real world, where personally phenotype is only about 50% heritable, it is hard to know if environment or genes best explains differences in personality between whole gene pools.

  8. […] As Razib points out, these studies involves a small sample. However, they are yet another piece of evidence pointing in the same direction as all the rest. […]

  9. The way others treat you has more to do with subconscious cues like body language than it does with physical appearance. Two people of identical appearance may be treated very differently based on the way they carry themselves. Essentially, these cues relay to others how you feel about yourself, which can be very heavily dependent on how your caretakers taught you to feel about yourself. Certainly there are genetic factors involved as well, but I think they’re being overstated here.

    • Replies: @Wow
    I was thinking the same thing.
  10. @Ozymandias
    The way others treat you has more to do with subconscious cues like body language than it does with physical appearance. Two people of identical appearance may be treated very differently based on the way they carry themselves. Essentially, these cues relay to others how you feel about yourself, which can be very heavily dependent on how your caretakers taught you to feel about yourself. Certainly there are genetic factors involved as well, but I think they're being overstated here.

    I was thinking the same thing.

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