Self-hiring is not a taboo, as long the candidate has experience from somewhere else. The usual expectation is that PhD + postdoc + first faculty job should involve at least two universities. Exposure to different ways of doing things leads to better research and makes the department less likely to develop an insular culture.

Postdocs are usually expected to move to a different institution, because most institutions don't have that many people working on the same topic. If you keep working with your former PhD supervisor, people may question whether the merits you claim are truly yours and not your supervisor's.

Hot take, but I don't think it should be such a taboo if individual institutions have "insular culture". As long as there is heterogeneity amongst relevant institutions, the synthesized literature can still be very productive even if e.g. MIT has a bias towards a particular way of thinking.

Conversely, I think it's problematic for scientific creativity how homogeneous behavior across institutions has become. I don't believe it is a result of this cross pollination requirement, but rather causality probably goes the other way. Many old professors at MIT were true lifers, from undergrad to PhD to faculty. Postdocs were often skipped entirely, or looked more like a 1 year visiting researcher gig.

Regardless I don't feel there should be a viscerally negative reaction to individual institutions having clear characteristics. It's true that objective evaluation is hard, but it's hard anyway honestly.

Institutions that grow too attached to their own ways risk becoming mediocre. People start caring more about internal politics than doing good research. Many European universities succumbed to that in the decades following WW2, due to a mixture of politics, loss of status, and poor funding.

> PhD + postdoc + first faculty job

You say this as if the expectation is only one postdoc these days.

>> 7.4% of professors have a Ph.D. from the same university that they are teaching at. MIT in particular has a high rate of self-hires, with 36% of their professors having MIT Ph.D.s themselves.

When you believe you're the best, you are probably going to be biased to hiring internally...

It's more likely that $RANDOM_UNIVERSITY wants to hire from MIT than the other way around.

Can confirm this. Attended the University of Northern Bumfuck, did not get hired by MIT.

I think I have observed a pattern where school tier k has professors who attended school tier k + 1.

If you are looking at the maximum tier, then there is no k+1 to draw from. So, you end up drawing from your tier, and, especially if your tier has few schools in it, you end up with a disproportionate representation of self-hires.

Oh, see, that's where you get universities that just don't grant tenure to assistant professors.