actually in classic evolutionary theory any biological trait is assumed to be normally distributed with with selective pressure acting against both sides of the distribution. a great blue herons legs for instance are assumed to be about their current length because for a herons ecolgical niche they represent the balence between the ease with which the heron flies and it's ability to wade in the depth of water were it mostly feeds (for example). if the heron's environment or niche changes genetic drift may occur such that now longer or shorter legs are selected for. many species show within species variation for traits that may be more advantageous in different parts of the species' geographic range, or over time with climatic fluctuation.
human IQ is typically represented as a normally distributed variable with a mean of 100 and a standard deviation of 15:
presumably human evolution is currently selecting for an IQ of about 100, which is BTW not that all that smart in the brainy scheme of things. individuals who fall too far below that average are less likely to pass their genes along because they are mentally retarded or just not that capable. individuals too far above the norm may be less likely to have kids because they are absorbed with intellectual or material pursuits and less social or less likely to see a large family as a source of happiness. it's important to keep in mind that IQ is a score on an IQ test and does not necessarily represent social skills or life skills, and certainly doesn't represent reprocuctive fitness, unless of course that bell curve is currently moving, which would in evolutionary terms would be hard to detect since evolution is typically described as taking place over more geologic time periods.
i wouldn't worry about it. the world will go on with or without your thomas pynchon reading, trad gear placing, weissbeer sipping, c++ programming genes, eh?
