Well, I expect that every shy nerd has noticed that it reduced his reproductive opportunities in high school. In extreme cases it can be a paralyzing illness that isolates to the point where drastic measures are considered. (For the original, see this.)
Apparently, though, shyness is not completely negative for evolutionary success. So, at least, argued Susan Cain in the New York Times Sunday Review (some years ago).
Yet shy and introverted people have been part of our species for a very long time, often in leadership positions. We find them in the Bible (“Who am I, that I should go unto Pharaoh?" asked Moses, whom the Book of Numbers describes as “very meek, above all the men which were upon the face of the earth.”) 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.
In the science journalist Winifred Gallagher’s words: “The glory of the disposition that stops to consider stimuli rather than rushing to engage with them is its long association with intellectual and artistic achievement. Neither E=mc2 nor ‘Paradise Lost’ was dashed off by a party animal.”
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.
Yeah, whatever. Fortunately most of us outgrow it, at least in part.