Huge data set shows 80% of US professors come from just 20% of institutions

Host: Nick Petrić Howe

Welcome back to theNature Podcast.This week: uncovering where most US professors get their PhDs.

Host: Benjamin Thompson

And the latest from theNature Briefing。I’m Benjamin Thompson.

Host: Nick Petrić Howe

And I’m Nick Petrić Howe.

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Interviewer: Nick Petrić Howe

We know a lot of you listening have PhDs, and if you’re part of the subset of that group who are US-based and working at an institution with tenure track, I might also be able to take a good guess at where you got that PhD, thanks to a new paper published inNature。本研究我们已经看了一个庞大的数据集英足总culty from 2011-2020 to get an understanding of where they were all trained and then where they ended up working. The answer may not surprise you. To find out more, I caught up with one of the authors, Dan Larremore, and started by asking him what we already know about US faculty.

Interviewee: Dan Larremore

Most faculty come from a minority of institutions, so there's inequality in faculty placement or production. And if you sort the institutions by which institutions they draw their faculty from, a social hierarchy emerges. It's not exactly a pecking order. These are endorsement interactions. If my institution hires a graduate from the University of New Mexico, my institution is implicitly endorsing the quality of the candidate that came from that institution. And so, if you zoom out, you can understand a hierarchy of prestige and endorsement, simply from the flows of faculty hiring. And past studies have identified in individual fields, in individual snapshots in time, that these kinds of patterns exist. What hasn't been known is whether or not these patterns are ubiquitous across fields, whether some fields show steeper hierarchies than others, and how these patterns are evolving over time.

Interviewer: Nick Petrić Howe

And so, given this kind of background, what was your motivation for your new paper? What sort of questions were you trying to answer?

Interviewee: Dan Larremore

This paper starts from the observation that oftentimes, when somebody gives a presentation, or is introduced as a speaker, or just introduced in general, one of the things that comes along with their name is their credentials. And this sort of raises a larger question of like, well, where do professors come from at a large scale? So, in this study, led by my graduate student Hunter Wapman, what we did was analyse all of the tenure-track faculty at PhD-granting institutions in the US over a decade. That amounted to around 300,000 professors, 368 institutions in around 10,500 departments.

Interviewer: Nick Petrić Howe

And when you looked at this data, what did you find?

Interviewee: Dan Larremore

Well, our first question was, where do professors come from? And we answered this first by looking at national origins. So, it turns out that around 11% of faculty come from outside of the US in their doctoral training. It’s not national origin, but around 11% of faculty have their PhDs from outside the US. It turns out that this varies a lot by field. So, for example, in education, 2% of professors got their doctorates outside of the US. In natural sciences, this was 19%. When we dig down a little bit further and we look at country of origin, we found that among those US professors who were trained outside the US, around 35% came from Canada and the UK alone. I want to contrast that with another number, which is the total professors who were trained doctorally in Africa and all of the Americas, excluding Canada and the US, and that was just around 5%. So, a huge fraction of the faculty who are coming into the US from abroad are trained in the UK and Canada, and a small minority are coming from Africa and the rest of the Americas.

Interviewer: Nick Petrić Howe

And you also then looked at people who got their doctorates within the US, and what did you find here? Where were these people coming from?

Interviewee: Dan Larremore

So, in the US, what we found was that there is stark inequality in production. What you might say is that the United States tenure-track hiring market is dominated by a small minority of institutions. So, for example, this follows the Pareto principle or an 80-20 rule, where 80% of US-trained faculty come from only 20.4% of institutions. Another way of looking at that is to say that 1 in 8 US professors comes from just 5 US institutions. And these five institutions train more than all of the non-US faculty combined. So, in general, what you could say is that the US faculty hiring market is really unequal in terms of where professors come from.

Interviewer: Nick Petrić Howe

And so, the places, this sort of 20% where 80% of the faculty are coming from, are they mostly prestigious universities, or do we not know this yet?

Interviewee: Dan Larremore

They are mostly prestigious. What we can do is actually measure prestige directly from faculty hiring networks. And in fact, what we find is that there's again inequality when it comes to prestige in these systems. So, basically, the elite positions in these hierarchies of prestige are occupied by just a few institutions, and most institutions have no departments at all that are in those elite top slots.

Interviewer: Nick Petrić Howe

And as I understand that is well, your data also gave some insights into the gender of the faculty. What are you able to tell me about this?

Interviewee: Dan Larremore

这是正确的。所以,我们也感兴趣standing gender inequality in the academy. And the first thing that we did was we looked year by year between 2011 and 2020 at the different fields and their gender representation over time. And essentially what we found is that women's representation has been increasing in almost every field, but not for the reasons that we might think. Because we could identify new hires and we could identify attritions, so people who left the academy early or who retired, we could compare women's representation in those inflows into the academy versus the representation of the outflows. And essentially what we find is that in almost every field there are more women who are coming in and more men who are going out. And when you look at the demographic curves, this really explains what's happening. Retirement-age faculty tend to be far more likely to be men than newly hired faculty. One question that we had was whether or not the percentage of women among newly hired faculty was itself changing over time. And we essentially found that hiring rates for women are flat over a decade of observation. So, what this is telling us is that the increases that we've seen in women's representation in the US academy have been driven by past changes in hiring, which are creating these demographic waves that are making their way through, or we have more men retiring and more women being hired. But what we don't see is continued change at the hiring stage. So, this is especially important for areas like mathematics and computing, engineering and natural sciences, where, still today, men are more likely to be hired than women, suggesting that without future efforts to change things at the hiring stage, we're unlikely to see gender parity over the next decade.

Interviewer: Nick Petrić Howe

You've found these stark inequalities in where US faculty are coming from. What sort of impacts do you think this could have on the sort of institution of science or the institution of education and learning?

Interviewee: Dan Larremore

Where faculty come from makes a difference in the questions that they ask. And in fact, their affiliations are known to affect things like paper acceptance rates. Prestigious affiliations increase the likelihood that one's paper gets accepted. Faculty-prestigious universities have more resources, they write more papers, they receive more citations and attention, they win more awards, and their graduates go on to experience greater wage growth. So, we know that where professors come from and these affiliations are really important for all kinds of markers outside of the quality of their ideas and the quality of their scholarship alone. So, in general, US faculty are coming from a highly stratified population, and that has impacts on what questions are asked and what people work on.

Interviewer: Nick Petrić Howe

That was Dan Larremore from the University of Colorado, Boulder in the US. For more on this story, check out the paper in the show notes.

Host: Benjamin Thompson

Coming up, we’ll be talking about the science of grieving for a public figure. That’s on the Briefing chat. Right now, though, it’s time for the Research Highlights, read by Dan Fox.

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Dan Fox

Chocolate may be one of the world's most popular foods, and cacao trees, which produce the seed kernels used to make chocolate, are also popular with a variety of wildlife. Researchers wanted to quantify how the different species living on small-scale cacao farms collectively affect production. The team marked out mini plots of cacao trees in a cacao-growing region of Peru. Some plots were surrounded by a cage of bamboo poles and fishing mesh that excluded birds, bats or both. One tree in each mini plot was treated to exclude ants, and flying insects were excluded by bagging one branch per tree in fine mesh. They found that flying insects, birds and bats all increased the total amount of cacao grown, probably because insects pollinated the flowers and birds and bats provided pest control. Trees that were accessible to birds and bats had more than doubled the yield of trees that were not. The authors think that the future of agriculture lies in fostering biodiversity, which can support high productivity. Read that research in full in theProceedings of the Royal Society B。

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Dan Fox

Large planets orbiting massive stars a great distance might have been adopted or stolen rather than home-grown. Scientists have seen Jupiter-sized exoplanets orbiting stars that are more than three times the mass of the Sun, but the size of such planets is a puzzle, as the conditions around these massive stars should stunt planetary growth. Researchers modelled the dense stellar nurseries in which stars are born and found that at least once within the nursery’s first 10 million years, a massive star is likely to steal a planet from a neighbour or adopt a free-floating wanderer. The authors predict that such planets would end up hundreds of times as far from their star as Earth is from the Sun. And this work backs the theory that planets on the most distant orbits originate from outside their current star system. Read that research in full inMonthly Notices of the Royal Astronomical Society。

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Host: Benjamin Thompson

Finally on the show, it’s time for the Briefing chat, where we discuss a couple of articles that have been featured in theNature Briefing。Nick, what have you got for us to talk about this time?

Host: Nick Petrić Howe

Well, Ben, as you and many of the people listening to this podcast will know, the Queen has recently passed away. And I've actually been reading a bit about the science of grief. We've got an article inNatureabout it and how it relates to public figures.

Host: Benjamin Thompson

Well, we're recording this on Tuesday, Nick, and the period of national mourning has just ended. And of course, there were a lot of people around the world who very much were grieving, who were in mourning.

Host: Nick Petrić Howe

Yeah, and the first thing to say about this is the people interviewed for this, these experts on grief, they emphasise that this is real grief that people are feeling, even though it's a figure they may never have met. And that's the sort of interesting part of this because why would it be that you would feel this way about someone you've never actually met, and that's sort of what this story delves into.

Host: Benjamin Thompson

Right, so in many cases, there is kind of a distance between the person who has died, in this case, the Queen, and those who are experiencing grief. What are researchers saying about this then?

Host: Nick Petrić Howe

Well, the first thing to caveat this with is we don't know a lot about grief. Grief is quite a hard thing to study because we're not exactly sure what it is, like it's a very complicated combination of emotions. But what we do know is that it can arise due to a sort of disruption of our experience of the world. So, we have assumptions of how the world is, like the Sun will rise, and when something like this happens, even when it's a public figure, our assumptions can be sort of shattered. Those things that we've thought and expected all our lives are now suddenly not the case anymore. Like the Queen has been around for my entire life and suddenly she's not there anymore, and this can cause sort of feelings of grief. And then there's also the fact that many people will identify with a public figure like the Queen. They'll share similar values or, in fact, their person, like how they define themselves, will be in part defined by this person. Maybe they feel very British, and being very British to them means that they honour the Queen. So, there are lots of different reasons why people may be mourning the Queen in this particular case.

Host: Benjamin Thompson

And so, what are the researchers in this news article saying then about the process of grief, right, because obviously it can be very different for different people.

Host: Nick Petrić Howe

It can indeed and, in this case, what the researchers are saying is that because it's a public figure, it's likely that it'll pass more quickly than other kinds of grief because the length of grief is often to do with the time, proximity and closeness that someone has with someone else. And so, because this is a public figure that they've not actually shared a lot of time with and are not personally very close to, they will probably come to terms with this much more quickly. And also, to come to terms with it, some of the researchers were saying that they will find qualities in the Queen that they admire and they will carry them forward. They’ll be like, I like the way that she wasxand therefore I will carry that forward, and that's how people sort of come to terms with this as well. But again, like I say, grief is a very complicated thing. It's not like there's a grief gland in your brain that just starts pumping out chemicals when someone dies, so it's a very complicated process and there's a lot that we don't know about it. But that's all for my story this week, Ben. What have you got for us to discuss this time?

Host: Benjamin Thompson

Well, Nick, the story that I've got this week, I read about it inThe Guardian, and it's based on some research published in the journalCurrent Biology, and it's an example of what's being dubbed an ‘interspecies innovation arms race’, and it's occurring in Australia between sulphur-crested cockatoos and humans.

Host: Nick Petrić Howe

Okay, so, pray, tell me what is an innovation arms race and why are cockatoos doing it with humans?

Host: Benjamin Thompson

嗯,很整洁的一个,因为它是关于social learning between the groups, right, and I'll come to that in a bit. But let's have a little bit of background here. So, this story centres on wheelie bins. Now, these are rubbish bins or trash cans, I guess, on wheels, as the name suggests, and folk leave them out once a week and their rubbish gets collected by the trash van. And these bins have hinged lids, okay? And cockatoos are very, very smart birds. And a team of researchers showed a little while ago how the birds learnt how to open the hinges on these things and get the waste food inside. And the researchers showed that this skill was passed from one cockatoo to another, and this behaviour spread very rapidly through the suburbs of Sydney. And now these researchers are back and they're looking at the human response.

Host: Nick Petrić Howe

好吧,如果我是一个人,我可能会尝试和停止them getting in by maybe putting a little clasp on the bin to stop it being opened, something like that.

Host: Benjamin Thompson

Well, that would be a good way of doing it, Nick, but there's a problem with that. The problem is you can't lock these bins down, right. They need to be opened and emptied by the automated garbage truck, right, so you can't just lock the bin.

Host: Nick Petrić Howe

Tricky.

Host: Benjamin Thompson

因此,生活在这些地区的人来了p with different ways to stop the cockatoos getting in. And the researchers behind this work have surveyed a few of these suburbs, looked at the areas here, and they've showed that there's a variety of methods that are used, right? I mean, a rubber snake was one of them. One of the most popular ones is just putting a brick on top of the bin. But the problem is cockatoos, they're pretty clever, and they learn to push those bricks out the way and then get in, right. So, there's some escalation of the protection that was shown in some areas, and the humans got more creative. Shoes jammed into the hinges is one, so the bin lorry can still open it but the cockatoos can't. Zip tying water bottles on top. And the researchers showed that protection was more common in areas with more cockatoo bin raiding, which is what you'd expect. But things do get interesting when you look at the areas, okay, and there's a spatial element to this.

Host: Nick Petrić Howe

Right, so the prevention strategies work better in some areas rather than others or something like that?

Host: Benjamin Thompson

Well, what the team have revealed is that some of the techniques used appear to be clustered in specific areas, right? So, some people would learn the same technique as their neighbours, right? So, if they could see the house across the street, they might give that a go. But houses that they couldn't see each other, like the house on the street behind, there wasn't that kind of clustering, right, so it seems like there's this kind of interesting dichotomy here. So, there’s this socially learned behaviour for the cockatoos on how to get into the bins, and then there’s this socially learned sort of defensive mechanism in the humans to protect their bins as well.

Host: Nick Petrić Howe

Right, okay, so this is the innovation arms race that you talked about the start.

Host: Benjamin Thompson

Yeah, that's right. So, each population is learning and escalating, where required, and I think one of the questions is, how far will this go? Will the cockatoos learn from each other and pass on that knowledge of how to get round the shoes trapped in the hinge, if they can get round it at all, for example. And what's neat is that there's also examples in this work of de-escalation as well, like in in some areas where the cockatoos stop trying to get into the bins, the people there stopped trying to protect them, and the reasons why they stopped isn't fully understood, but maybe less trash was being thrown out in these areas. So, lots of questions to answer about sort of the social learning and this innovations arms race.

Host: Nick Petrić Howe

Wow, that's super interesting, Ben. And if there are any aspiring sci-fi writers out there, Interspecies Innovation Arms Race is quite a good name for a novel. But listeners, if you're interested in those stories and want to read more about them, and for where to sign up to theNature Briefingto get more like them to your email, check out the show notes.

Host: Benjamin Thompson

And that's all for this week. But just before we go, there's time to mention that we've got a new video on our YouTube channel. It's all about flying robots that 3D print millimetre-accurate structures, and you can find a link to that in the show notes.

Host: Nick Petrić Howe

And as always, you can keep in touch with us over on Twitter – we’re @NaturePodcast. Or you can send us an email to podcast@nature.com. I’m Nick Petrić Howe.

Host: Benjamin Thompson

And I’m Benjamin Thompson. See you next time.