I have previously pointed to the work of Jerome Kagan at Harvard; who, along with others, has shown that some of us are born with a predisposition to be timid and more anxious. The temperament we display in early childhood (introvesion versus extroversion, high versus low reactivity, anxiety in unfamiliar versus familiar situations, etc) is largely genetically determined and persists through life. In this vein Susan Cain has recently offered an interesting article on shyness. She first notes the re-framing of shyness into "Social Anxiety Disorder" by drug company TV adds seeking to sell serotonin reuptake inhibitors (S.S.R.I.), cited Zoloft advertisements:
...the ad’s insinuation aside, it’s also possible the young woman is “just shy,” or introverted — traits our society disfavors. One way we manifest this bias is by encouraging perfectly healthy shy people to see themselves as ill...Social anxiety disorder did not officially exist until it appeared the 1980 Diagnostic and Statistical Manual, the DSM-III, the psychiatrist’s bible of mental disorders, under the name “social phobia.” It was not widely known until the 1990s, when pharmaceutical companies received F.D.A. approval to treat social anxiety with S.S.R.I.’s and poured tens of millions of dollars into advertising its existence...Though the DSM did not set out to pathologize shyness, it risks doing so, and has twice come close to identifying introversion as a disorder, too. (Shyness and introversion are not the same thing. Shy people fear negative judgment; introverts simply prefer quiet, minimally stimulating environments.)Cain's article continues with an interesting discussion of the respective advantages and disadvantages of being a sitter or a rover.
...shy and introverted people have been part of our species for a very long time, often in leadership positions...We find them in recent history, in figures like Charles Darwin, Marcel Proust and Albert Einstein, and, in contemporary times: think of Google’s Larry Page, or Harry Potter’s creator, J. K. Rowling.
...We even find “introverts” in the animal kingdom, where 15 percent to 20 percent of many species are watchful, slow-to-warm-up types who stick to the sidelines (sometimes called “sitters”) while the other 80 percent are “rovers” who sally forth without paying much attention to their surroundings. Sitters and rovers favor different survival strategies, which could be summed up as the sitter’s “Look before you leap” versus the rover’s inclination to “Just do it!” Each strategy reaps different rewards.
IN an illustrative experiment, David Sloan Wilson, a Binghamton evolutionary biologist, dropped metal traps into a pond of pumpkinseed sunfish. The “rover” fish couldn’t help but investigate — and were immediately caught. But the “sitter” fish stayed back, making it impossible for Professor Wilson to capture them. Had Professor Wilson’s traps posed a real threat, only the sitters would have survived. But had the sitters taken Zoloft and become more like bold rovers, the entire family of pumpkinseed sunfish would have been wiped out. “Anxiety” about the trap saved the fishes’ lives.
Next, Professor Wilson used fishing nets to catch both types of fish; when he carried them back to his lab, he noted that the rovers quickly acclimated to their new environment and started eating a full five days earlier than their sitter brethren. In this situation, the rovers were the likely survivors. “There is no single best ... [animal] personality,” Professor Wilson concludes in his book, “Evolution for Everyone,” “but rather a diversity of personalities maintained by natural selection.”
The same might be said of humans, 15 percent to 20 percent of whom are also born with sitter-like temperaments that predispose them to shyness and introversion. (The overall incidence of shyness and introversion is higher — 40 percent of the population for shyness, according to the psychology professor Jonathan Cheek, and 50 percent for introversion. Conversely, some born sitters never become shy or introverted at all.)