Intellectually inbred individuals who whose intellectual experience is limited to a single domain, culture or genre.

Western culture has historically been very good at turning out individuals who are blind to the glories of other cultures. Intellectually inbred individuals also include:

You're likely to be intellectually inbred if you receive more of your intellectual fodder by a single genre (sci fi, modern novels, classic literature, comics, technical documentation, newspapers, TV, films, pulp romances, civil war documentaries, wildlife documentaries, the WWW, UseNet, E2, MTV, …) than all other genres put together.

Many geeks are intellectually inbred, many for example assume that Unicode contains no embedded cultural assumptions (hint: it assumes the primacy of written language); that most modern languages are easily representable on the internet (hint: try Hindi) and that Robert A. Heinlein invented utopian novels.