I sometimes suffer extrovert envy. I just returned from a vacation at a small all-inclusive resort in Mexico. The vacation was lovely and I have no complaints, only an observation: It seemed like extroverts got more gracious service. I certainly can't blame the staff for responding positively to outgoing energy.
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 extraversion is calibrated according to phenotypic features.