system
Given the following post, respond as if you're commenting on Reddit:
human
Does it mean anything if professors at a university got their PhD at that same university?

Im looking at engineering PhD programs \(US universities\) and notice at one university in particular that several professors \(at least 5\) within the department got their PhD from that same department. Three of them even all had the same PhD advisor. They range from early career to mid\-late career \(30 to 50 years old\). It is well known US university ranked in the top\-10 for many areas of engineering. 

Some people have told me this is a bad sign. Is it? why or why not?
gpt
It's not necessarily a bad sign, but usually the feeling is that an academic should leave their graduate institution for the next steps in their career for a few reasons:

* Exposure to other philosophies at other institutions, broadening one's experiences.

* Flip side of this, the department usually wants to bring in people from other institutions to benefit from their different perspective learned at their previous department.

* To spread the prestige of the graduate institution (not always a factor, but some people care about this).

* Probably the big one is to spread out collaborator networks and more importantly funding. If you have several professors at a university working in the same area as their advisor, that can make it more difficult to bring in funding - either you have multiple separate teams competing in the same field, or you have fewer external collaborators to strengthen a multiple-PI proposal (especially if you haven't gone beyond your first university to build a network). You may also see higher competition for grad students with several professors working in such closely-related areas.

* There can sometimes be an issue with nepotism if several of these faculty have the same advisor who is a very senior member of the department. Even if they're not a department head, that advisor may have an excess of political power in the department due to having essentially lackeys to back them up.

All that said, these are just benefits from leaving your graduate institution (except the last factor) - it's not a *bad* thing to stay put, if you like the location for living in (a very underrated factor!) or the institution is a completely premiere location for your kind of research and simply the best option. Alternatively, some professors will have moved around a few times, e.g. after earning a PhD, someone might do a postdoc somewhere, go into industry for a while, spend a few years at a national lab, and then return to their first institution as a faculty member. So it may not mean anything, but if you see other warning flags it could be a bad sign in combination with those.