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In an article titled "The Origins of Extraversion: Joint Effects of Facultative Calibration and Genetic Polymorphism" researchers Aaron W. Lukaszewski and James R. Roney at the University of California, Santa Barbara posit that is calibrated according to phenotypic features. Specifically, that if you're good looking and strong, you are likely to be extroverted.

OK, it's a bit of a sucker punch for introverts. But let's put on our big-girl pants and take a look at it.

We know about the interaction between nature and environment. For example, people respond differently to infant girls and boys, which starts the developmental process of culturally created differences. (Which is not to say that all gender differences are due to environment. I don't know and that's a whole other discussion.)

These scientists suggest something similar for extroversion: That good looking, strong babies and children are rewarded with lots of , which causes them to respond in kind, and a social style is born. The researchers found this effect even when controlling for androgen receptor polymorphism, a genetic explanation for extraversion, among other traits.

"All humans are equipped with a universal facultative mechanism that calibrates on the basis of feedback cues over the course of development," said Lukaszewski in a phone interview. "Even at a very young age, people respond more positively to healthy-looking physically attractive people. Those sorts of feedback cues can be influencing mechanisms in development."

The studies Lukaszewski and Roney undertook relied on various measures, self-reports and ratings, and independent ratings of using standardized photos.

I looked at the measure they used for extroversion and I'm not wild for it. IPIP Extraversion measures four facets of extroversion: Expressiveness, Liveliness, Sociability, and Social Boldness. Items are weighted either positively (indicating more extroversion) or negatively (indicating less extroversion and therefore more ).

But the items don't all ring true to me as they relate to introversion.

Under Expressiveness, "Bottle up my feelings" is weighted negatively, but that doesn't describe introverts. One could argue that introverts are less likely to mask our feelings with a lot of activity and fuss, that we feel them deeply and express them as we feel is appropriate.

Under Social Boldness, "Would be afraid to give a speech in public" is negatively keyed. Nope, that's not right either. Lots of us are fine speaking in public.

Under Sociability is "Rarely enjoy being with people." Nope again. Depends what people, how many, how long.

Under Liveliness, "Feel that I have a lot of inner strength." is positively keyed, making it an extroverted quality. Really?

And this, from one of Lukaszewski's emails troubles me: ...the fact that the extraversion continuum is not called the introversion continuum is purely arbitrary, following the de facto convention of labeling based upon the more "socially desirable" pole.

That doesn't sound arbitrary, and it doesn't sound good, although Lukaszewski stresses that introversion has its own rewards.

But Lukaszewski's theory is entirely plausible. If you're good looking, you get a lot of attention and getting that attention becomes part of who you are.

But then you have someone like, say, Julia Roberts, who is both beautiful and introverted*.

Lukaszewski said, "It can also be the case that through experience the child learns that how they get a lot of positive attention and rewards is developing skills that are facilitated through a more introverted orientation."

In other words, you can be genetically wired for extroversion but be rewarded for introverted behavior, therefore developing an introverted .

Also plausible.

Still my brain gets a little tangled up in this theory. It's kind of annoying, but can't be rejected out-of-hand.

Certainly attractive, strong people are socially rewarded everywhere, and that must affect development. And, as Lukaszewski points out, many people are also rewarded for introverted behavior--anyone who grew up in a bookish house knows that. That could affect the social style of someone wired for extroversion.

So, OK, a case can be made for physical attractiveness increasing extroversion. But is the inverse true? Does unattractiveness increase introversion?

I think this research adds to the discussion about whether introversion and extroversion exist on separate continuums. Putting negative weights on an extroversion scale doesn't seem to measure introversion.

Still, it does give us something to chew on.

How much of your introversion do you think is developmental, because you were rewarded for it? And remember that what families say ("Come out of your room!") and what they reward (high grades) isn't always consistent.

If you are among the swashbuckling introverts, do you think that's because you were rewarded for extroverted behavior?

And either way, do you think looks have anything to do with it?

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Photo by David Shankbone via Flickr (Creative Commons).