Do universities prefer not to hire their own PhD graduates in faculty positions?

At my university - or at least in my department - the norm seems to be that they prefer to hire externally for tenure-track jobs (speaking from experience serving on a search committee for a tenure-track position). The line of reasoning is, "if we're the ones who taught/mentored/molded Candidate X, then they're not bringing in anything new in terms of scholarship."

This is less applicable to non-tenure track jobs, as those faculty members are usually teaching lower level classes and don't have any research obligations. There are several PhD faculty members in my department that were hired internally who work as lecturers.

Anecdotal, of course, but I've studied at/worked at a few universities over the years, and this is the pattern I've tended to see. Tenure-track: external. Non-tenure-track: internal OK.

As there is no "US" tag, the German universities have a general and quite strictly enforced policy that no one may be "simply" given a professorship at the same university where they were postdocs. No Hausberufung.

The rule is about "promoting" people to professors internally. If you were somewhere else, it's not a problem. If you have a position offer from somewhere else it should not be a problem.

The basic idea is to "validate" people in tenure positions from outside and to prevent folks "growing into" a tenured position from a life-long career at the same place.

2nd hand knowledge here, take with a grain of salt:

In the university I'm familiar with, a PhD who wants a career in the same university is required to do several post-docs abroad.

This makes following career paths possible:

• PhD at A, post-doc at A, career at B
• PhD at A, post-doc at B, career at A
• [and more complex]

This seems like a compromise between your original statement, your post-doc link and appointments from within the organisation which could lead to cronyism.

I believe there's deeper rationale at work as well, scientists' responsibility is not only research but also spreading the knowledge and methods. An arrangement like this ensures that both A's progress is shared with B, as well as B's progress is brought into A.