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.
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 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.