While elite universities, with their deep resources and demanding coursework, surely produce great professors, the data suggest that faculty hiring isn’t a simple meritocracy. The top schools generate far more professors than even just slightly less prestigious schools. For example, in history, the top 10 schools produce three times as many future professors as those ranked 11 through 20.
One explanation for this skewed hiring system is that lower-prestige institutions are trying to emulate their high-prestige brethren. For a university, the easiest way to burnish your reputation is to hire graduates from top schools, thereby importing a bit of what made these institutions elite in the first place, while signaling to prospective students and faculty that you attract top talent.
Another factor could be that it’s not easy for schools to evaluate job applicants on merit alone, because merit can be difficult to define or measure. In the tenure system, a professor might work at the same institution for 40 years. But when hiring for tenure-track positions, schools often have to guess about lifelong productivity based on just a few years of experience. Hiring faculty is therefore a high-stakes decision; while you can always deny someone tenure, doing so means you’ve wasted years nurturing talent that you don’t want to keep. With so much uncertainty involved in the process, it may be natural to go with what seems like a safe choice: an applicant trained at a high-prestige school, even at the expense of exciting candidates from slightly less elite institutions.