Revisiting Bolnick et al. 2003

In a paper published in The American Naturalist in 2003, Daniel Bolnick, Richard Svanbäck, James A. Fordyce, Louie Yang, Jeremy Davis, Darrin Hulsey and Matthew Forister reviewed studies that examined individual specialization on resource use and quantified how much inter-individual variation contributes to a species’ niche width. Based on their review, they discuss the ecological, evolutionary and conservation implications of individual specialization, especially in relation to resource use and population dynamics. Thirteen years after the paper was published, I spoke to Daniel Bolnick about the motivation to do this study, his collaboration with the other authors, and what we have learnt since about the role of individual specialization in ecology and evolution.

Citation: Bolnick, D. I., Svanbäck, R., Fordyce, J. A., Yang, L. H., Davis, J. M., Hulsey, C. D., & Forister, M. L. (2003). The ecology of individuals: incidence and implications of individual specialization. The American Naturalist, 161(1), 1-28.

Date of interview: 21st December 2016 (via Skype)

 

Hari Sridhar: I wanted to start by asking you about your motivation to write this paper. By looking at your publication list, I came to know that this was something that was published around the end of your PhD. Did the motivation for this come from the other work that you did in your PhD?

Daniel Bolnick: Yes, it came out of actually a disagreement that I had with one of my PhD committee members. So, I was, for my PhD, mostly interested in understanding how intraspecific competition could generate disruptive selection. And I was interested in that because that formed a key element in some of the theories of sympatric speciation that were emerging at the time. And so, this notion – frequency dependent, disruptive selection – was something that was the driving force in for example, Dieckmann & Doebeli 1999 in Nature, Kondrashov & Kondrashov in the same issue of Nature. And most of the debate in sympatric speciation was focused on, well, how does this selection change the mating dynamics and reproductive isolation? But everybody was so focused on that, that I felt that the disruptive selection itself was being taken for granted. That wasn’t the focus of the debate; instead, it was just an input assumption. And so I set out to test that notion that competition generates disruptive selection. And it’s predicated on an even earlier assumption that phenotypically unusual individuals eat something different than phenotypically common individuals, and that’s why they escaped resource competition. And so, the presumption then is that individuals within a population differ in what they eat. And I, coming from a fish trophic polymorphism background took that idea for granted. Right, but Tom Schoener disagreed with me on that. And during my proposal defence, he challenged me on this and said, well, there were some theoretical models in the 70s and 80s that said that there shouldn’t be very much individual variation in diet. And that perspective didn’t mesh with my own view of the empirical literature. and so I basically set out to prove Tom Schoener wrong; in a friendly way. I mean, I have really amazing respect for Tom Schoener. He’s one of the great foundational figures in ecology. But I felt that I needed to prove that point. And so, rather than tackle that myself, I called together a few other graduate students who were interested in somewhat overlapping ideas. And we, as a group brainstormed about how to approach it and reviewed the literature together.

 

HS: Were the other authors are graduate students?  I noticed one author was from Sweden..

DB: Yeah, Richard Svanbäck. He was a visiting graduate student. He had a one year fellowship to come from Sweden, where he was doing his PhD, to visit Davis.

 

HS: Before I ask you more about the paper, I just want to step back a bit and ask you how you got interested in these topics?

DB: Um, yeah, I had quite a diverse set of interests early in graduate school. And I floated around between a variety of ideas, but I think I was generally interested in speciation and in the geography of speciation. And as I read more and more about it, the then very intense debate about sympatric speciation caught my attention as a place where there was progress to be made. And there is quite a large literature in fishes about morphological variation within populations and diet variation within populations as a precursor step to speciation. So, whether it be the Cameroonian Crater Lake cichlids that Uli Schliewen wrote about in 1994, or Arctic char, or David Sloan Wilson’s work on Sunfish, and of course the stickleback literature, all of that made me predisposed to accept that there would be among-individual variation in diet and morphology in a way that Tom Schoener was not initially prepared to accept.

 

HS: Could you tell us a little bit about how the work in this paper actually got done?

DB: Yeah, so we had a series of meetings over the duration of a semester, a half year. Once a week, the grad students would get together… it started out with a much larger group of people and over time, because everybody was busy, various people dropped out of the group. So we met once a week and we would read some papers together. Some weeks we would all read a single paper and discuss it and some weeks everybody would read a different paper and come together and tell briefly about what they had inferred. And after maybe two months of that, we built an empty table where we had many columns representing different bits of information – What’s the species? What’s the evidence that there’s individual variation? What’s the time scale? Is it genetic? and so on. And that table that forms the backbone of our American Naturalist paper was really one of the first things that happened. So we built that table early on, and the idea was, each person in the group would pick some set of organisms or some set of papers to review. And we’d spend time searching the literature to find examples to add to the table and, over time, we built that table as a group, different people adding different entries, and then each entry would be double checked by a second person to make sure they agreed with the characterization. And then at the end of maybe two more months, we had the table complete. And we spent some time brainstorming what an outline manuscript would look like. And then over the summer that followed that semester, I was doing field work up on Vancouver Island for my empirical side of my research, and I had some spare time while the experiment ran. So I spent that time writing out that paper in text form, sent it to co-authors, they commented on it and we submitted it. So it was a graduate student discussion group that led to building the table that led to the paper.

 

HS: Wow. So this would be the summer of 2001, when you wrote up the first draft of the paper?

DB: Let me think, it must have been 2002.

 

HS: The paper that says submitted in August 2001.

DB: Okay, then it must have been 2001. So my memory was clearly off on that.

 

HS: There are two or three earlier papers – conceptual & theoretical work – that you discuss quite a bit in the paper. One is Van Valen’s niche variation hypothesis, then a couple of papers by Roughgarden (1,2), and then the paper by Taper and Case. From reading your paper, it seems like these were fairly influential in the discussions that went into the paper. Is that just my reading of the paper or were these papers, in fact, sort of central to the ideas you were developing?

DB: I think they were, but in some sense, we were developing the ideas and discovering those papers, simultaneously, that provided a bit more historical context to things that we were thinking about independently. As you we’re introducing that list of papers I kept expecting you to list one additional one that you didn’t mention  – Smith & Skulason.  I’d say that one may have been more influential because of what it didn’t cover. So, Smith & Skulason is very much about these discrete, recognizable polymorphisms where the animals are distinctive enough that you can easily categorize them into one group or the other. And in a sense, this paper was filling in what we perceived of as a gap, that didn’t really fit Smith & Skulason. And in fact, some of the case studies from Smith & Skulason, we felt, much better fit our characterization of individual variation rather than trophic polymorphism, the way they defined it. And so it was also, in a sense, an extension to that previous study.

 

HS: I wanted to ask you about your definition of an individual specialist.  You define “an “individual specialist” as an individual whose niche is substantially narrower than its population’s niche for reasons not attributable to its sex, age, or discrete (apriori) morphological group”. And later, you also say, “individual variation and polymorphism are ends of a continuum of increasingly discrete variation.” Today, if you were to revisit that definition, and the link of individual variation to polymorphism, would your thinking be more or less the same?

DB: Yeah. I’d I often tend to use the word just intra-specific or within-population variation as an umbrella term that encompasses all of those. And there are instances where I feel like it’s maybe more appropriate to use that terminology. That’s a little more agnostic about how that variation is structured. And so I feel like ontogenetic niche shifts and sexual dimorphism and diet and individual specialization and trophic polymorphism really are different, although they intersect to some degree. And they have some slightly different consequences that I don’t think anybody’s really formally laid out yet. I don’t think that there’s been a sufficient side-by-side comparison of the dynamical properties of populations and communities under those different scenarios. But I do think of them as different still, although now and at the time, I recognized that they were related; hence that comment about the continuum.

 

HS: I want to revisit Figure 4. In relation to that figure you say that, although the evidence is fairly small, within-individual variation is probably greater than between-individual variation. Has been work subsequent to this paper, looking at individual variation within populations of different species? Now, do we have a better idea of the relative importance of these two?

DB: I’m pulling up Figure 2. This is the drawback of discussing a paper that I published 13 years ago  – I don’t actually remember it very well.  Yeah, so, absolutely. We had another follow up paper in Ecology Letters –  the primary author was Marcio Araujo – that re-reviewed this literature; It’s basically – 10 years later, how much more do we know? And it creates a figure that’s quite similar to this one, updated with double the number of case studies. And I’d say the distribution looks fairly similar. But certainly at the time, this was not a very substantial data set. It’s gotten better, and I think it’s held up well to scrutiny over time.

 

HS: Does the more recent paper have an updated table with new examples?

DB: I don’t think it’s a large table. There might be a table in the supplementary materials for that one, but the Marcio’s paper does not have an in-print version of a large table.

 

HS: So you would say that the takeaway from the 2011 paper is also that WIC > BIC?

DB: Um, Yes. And I’m looking at Figure 2 of the Araujo et al. paper now. I’d say actually from that figure that it’s a bit mixed. There are certainly some systems where the trend is actually towards BIC being larger. And there’s quite a range. And of course, there’s estimation error. So it’s hard to be entirely confident about the underlying distribution. But, yeah, I’d say, for the most part, that does hold up.

 

HS: Around the same time as this paper, you published another paper on the indices. Some of the authors are common to both papers. Were both these papers the outcome of the same project?

DB: They were.. How did that work? I guess I had gone to present our thinking about individual specialization, to Brad Shaffer’s lab meeting. I wasn’t in Brad Shaffer’s lab, but I thought it was a good opportunity to tell them what we were doing, and several of the co-authors were affiliates in his lab group. There was a tradition of hanging out and having a beer after lab meetings. And in that after-presentation time over some beers, we got into a fairly active discussion about how exactly you quantify these things. We pulled up literature search there and then, and found a few possibilities. And we came up with some of our own, had a very late night brainstorming session and put together the bulk of that paper – at least the outline of it  – there and then, that particular evening, I’d say it was one of the most productive single evenings I’ve ever had.

 

HS: The index that you talk about here – WIC/TNW  – is that still the most commonly used to quantify individual variation?

DB: I think it is. I think it’s a mix of that one, and the IS – individual specialization index  -which is based on pair-wise similarity Index, basically the extension of Schoener’s index. That does seem to be the most commonly used.

 

HS: You say, “individuals appear to vary in their “personality type,” some being more risk averse than others, possibly reflecting different optimization rules”. In terms of the history of these ideas, was this like a precursor to the development of ideas related to animal personalities in behaviour?

DB: Yeah, that’s a good question. So we were writing this simultaneously with Alison Bell and Andy Sih writing about behavioural syndromes. And Alison and Andy were housed in a different building at UC Davis. Davis has a huge biology program and multiple departments. They were over at Animal Behaviour. And they were having basically the same conversations that we were. They were having it very much from a behaviour standpoint, we were having it from an ecological dietary resources standpoint.  But we were addressing the same ideas simultaneously, about 300 meters apart! And didn’t know it! And it was only after our respective papers were published, that we realized that that had been happening.

 

HS: Okay, that’s interesting. At the time did you did you know Alison Bell and Andy Sih?

DB: Yeah, I certainly knew them socially. But we just hadn’t had the opportunity to talk about those specific projects. Alison was actually, at the time, also working on three-spined stickleback, as was I. So we were working on the same organism, asking similar questions. And we met fairly often to talk about some of the mechanics of working with our organism. We talked about our respective research interests, but when we did, I might maybe talk more about the disruptive selection side of things and she talked more about the endocrine control of behaviour. And so we didn’t quite click about this shared interest.

 

HS: Can we go over the names of the people you acknowledged to get a sense of how you knew these people and how they helped?

DB: Yeah, of course.

 

HS: L Ferry-Graham.

DB: Yeah, so that’s Lara Ferry-Graham. She was a post-doc in Peter Wainwright‘s lab. That was the lab that I was in. And we just had quite a few conversations about this. She was interested in specialization. She and I had written a opinion paper the year before about definitions of specialization. It wasn’t focused at the individual level. But she had been involved in those conversations.

 

HS: M. Graham.

DB: Mike Graham was also a post-doc and somebody who I just had extensive conversations about this with.

Beren Robinson is next. He was a post-doc with Dolph Schluter. And at the time that we were working on this, he was starting his faculty position where he is now, at the University of Guelph in Canada. And he had been thinking about very similar issues. And I found out that he’d been thinking about similar issues. So he and I had a correspondence about the topic.

 

HS: A. Shapiro.

DB: Yeah, that’s Art Shapiro. I started out working with him for my PhD and then I switched into Peter Wainwright’s lab. Art read a version of the manuscript, and gave us comments, as did Peter Wainwright, the next person listed.

I don’t actually remember who… Oh [laughs], D Weiss. That’s not a name I’ve read for a little while. That’s my wife! She’s now Deborah Bolnick. She gave us comments on the paper. And then David Sloan Wilson had written very closely-related things.  He was a reviewer on this paper and signed his review.

 

HS: J. Lau.

DB: Yeah, that’s Jen Lau. She was a fellow graduate student, as was Andy McCall, and Ben Sacks. They were all, early on, members of this discussion group, but they faded away in their interest in participating, as they got busy and we started delving down into fine details.

 

HS: The authors on this paper, you said, they were all graduate students in your department. Were they from different labs?

DB: Yes. They were mostly from different labs. Let’s see  – I was in the same lab as Richard Svanbäck, who was visiting. And I was in the same lab as Darrin Hulsey. Jim Fordyce and Matt Forister were just down the hall from me, in Art Shapiro’s lab. Jeremy Davis was..I forget whose lab he was in, actually. And then Louie Yang was a student in Rick Karban’s lab.

 

HS: How did you decide to submit this paper to The American Naturalist?

DB: Well, our first thought was to submit it to Annual Review of Ecology and Evolution. Brad Shaffer, who I mentioned already, was on the editorial board, and he discouraged us from doing so. And so The American Naturalist seemed like… it was a place where some of the back literature that we were citing had been published. And so it seemed like a good choice.

 

HS: Would you say this paper had a relatively easy right through peer review?

DB: We had a very long set of reviews. They were encouraging. They were very encouraging, but I did a very substantial rewrite in response to the reviews. They guided us; and I’d say Mark McPeek, who was the associate editor, at the time who handled the paper, did a fantastic job of helping us hone the message.

 

HS: When the paper came out did it attract a lot of attention?

DB: I didn’t notice right away except for two things. One is Thomas Schoener, who I’ve mentioned previously, read it and told me that he was going to assign it as required reading in the introductory graduate class in our program. I thought that was a good sign. And then The American Naturalist had just started doing press releases at the time. And they did a press release on this. And it was picked up by Science Friday, which was a radio show on National Public Radio. So I ended up having a four or five minute interview on Science Friday on the radio. Other than that, I didn’t really get very much feedback on it for a long time. And so it came as a bit of a surprise to me, over time, to realize that it was getting widely read and cited as much as it was.

 

HS: And do you have a sense of what it gets cited for?

DB: Um, it gets cited a lot by, what I’d have to say is …there’s a cottage industry of studies that basically say, Well, we’re going to see if there’s individual specialization in our favourite species. And they’re often not very edifying to do that, but I think that’s probably a large part of the citations. And then also at this point, I think, often when authors are trying to make the statement that there’s a lot of individual variation within populations, this has become a default citation. Sometimes even when it’s not really the appropriate citation for the sentence that it’s put in. Somebody once told me – I think it might have been Michael Torelli – that the definition of a citation classic is a paper that everybody cites but nobody actually bothers to read. So, you know, you just over time learn that there are certain papers that you’re supposed to cite in certain contexts. And you do so as a knee-jerk reaction. and I think there’s an element of truth to that. It’s  meant partly as a joke, but I think there’s a little bit of truth.

 

HS: Would you say that this paper had a big impact on your career, and on the course that your research took after this?

DB: Absolutely. I still work on topics of individual-level variation within populations. And I think this paper, because it was well received,  very much helped me get my faculty job. It received – it was explicitly the basis of – one award from the Ecological Society of America, but it also, I think, helped with some others. And, you know, once you get some awards, then you get more, and it gets easier to get grants. And so I think it was a very fortuitous start.

 

HS: Today, 13 years after this paper was published, could you say a little bit about where your thinking on these ideas stand today?

DB: That’s a little hard to answer, in part, because I don’t think I’ve read this paper since maybe 2004-2005. And it may be hard for me to separate out what I think now from what I thought then, without sitting down and re-reading it. But I think it stood up pretty well. I’d say I definitely had a fondness for optimal foraging theory at the time, that I’m a little less enthralled with now; but only a little! We didn’t really engage that much in some of the evolutionary causes of this as much as I might now. I think thinking about things like gene flow and other forms of negative frequency dependence – there’s a variety of things that could generate and sustain this individual variation, some of which are adaptive, some of which are non adaptive. I think I would have expanded on that. It’s a long paper already, but I certainly could envision writing more on that at the time.

 

HS: That’s something I wanted to ask you about. There’s a section in the paper where you talk about proximate and ultimate mechanisms underlying individual variation. And at that time, you seem to suggest that we don’t really know enough. Over the years since the paper was written, do we know more about the causes of individual variation?

DB: I think we know more; I don’t think we know enough yet. Starting first on the ultimate causes:  the more selective adaptive context – in a sense, that was the purpose of the Araujo, Bolnick & Lehmann paper in Ecology Letters. At the time that this American Naturalist paper came out, we basically said, Well, here’s a bunch of examples; So this phenomenon exists. Richard Svanbäck and I then did a series of papers after that, where we tried to experimentally test the role of interspecific competition in changing the degree of individual specialization. And so the Araujo et al. paper is really meant to talk a little bit more about ultimate mechanisms and say, What are the ecological processes that favour or constrain this individual variation? I think we do know a lot more about it, but since when would anybody ever say, Oh, yeah, we’ve solved that; we know enough. But yeah, I think we’ve come a long way in that regard. It bugs me still that there is a lot of the stamp collecting rather than hypothesis testing, Sort of a descriptive natural history approach to this question.

 

HS: And what about in terms of the proximate mechanisms?

DB: That’s, I think, where we know a lot less. You know, you really need to get more of a biomechanics and behavioural and neuro-ethological approach to this. And that’s something that I don’t think has happened substantially. Maybe partly because it’s much easier to do the neuro-ethology or the biomechanics between populations that are very different and so you have a large effect size. I think, studying the individual level variation, you just have a lot less power because you have a smaller effect size that makes it harder to study well. And I think that people have not really picked that up as well.

 

HS: In one place in the paper you talk about these different paths to individual variation. One is where the population niche width increases, and there are more resources to divide. And the other is where the niche width is constant, and individuals partition resources more finely. And you propose two hypotheses as to why individuals might reduce their niche rates. The first is that there’s intense intraspecific competition that may select individuals that use particular resources more efficiently, at a cost to their generality. At that point, you say  support for this idea comes from one particular study with pigeons, right. First, I wanted to know whether there’s more support for this today. Have there been other empirical examples showing this?

DB: Yeah, so we have an experimental example of that, that was published in Ecology and Evolution. The first author is Christine parent. And we use Tribolium beetles. Deepa Agashe was also on that paper, I think. So that’s another one where individual niche width shrank, much to our surprise, in response to competition.

 

HS: The other hypothesis is that if deleterious mutations have resource-specific effects, mutation accumulation in a population will produce individuals with restricted resource use ability. Is there evidence for this?

DB: No. Now that, we were grasping at straws, I think!

 

HS: One of the points you make in the takeaways from this paper is that individual variation needs to be incorporated into modelling of population dynamics. To what extent that has happened?

DB: Yeah, I think that maybe the most successful side of this endeavour.  Ecology has really picked up on this in the context of trait-based ecology. I do think that there’s been a lot of very nice work building individual variation into perspectives about species interactions and population dynamics. The material that I’m most familiar with… we had a Trends in Ecology and Evolution review paper that I lead-authored in 2011 that was very much building on this idea. And then Sebastian Schreiber had a paper in Ecology that I was on, where we laid out a way to fuse quantitative genetics with population dynamics, for this purpose. And Sebastian, in particular, has run with this idea. He’s had a couple of grants to work on that. He’s had a couple of additional papers and more coming out that really try to incorporate phenotypic variance into these eco-evolutionary dynamics and really ask what’s the role of variance per se in mediating outcomes of species interactions.

 

HS: The other thing you say, in relation to this, is that there haven’t been any theoretical treatments that have taken into account the effects of varying temporal consistency in specialization.

DB: I think that’s still true.  The only caveat – Mark Novak might have done some work on this. I haven’t followed all of his work lately. But he’s certainly thought a lot about the timescale of individual specialization. And so if anybody has done it, I’m gonna guess that Mark Novak would be the one who’s worked on that.

 

HS: You earlier said your interest in all of this started with speciation, and in one part in the paper you talk about the link between intra-population variation and reproductive isolation and speciation. You say that the conditions under which speciation will or will not occur are still poorly understood, in relation to this variation. Did you pursue those ideas in your own research after that, and do we know more about that now?

DB: Yeah, we do. There’s still more to be done. I had a graduate student, Lisa Snowberg who worked quite a bit on the relationship between mate choice and individual variation in diet, and showed that there was, in fact, assortative mating by diet. And I think that certainly panned out as being a very interesting direction to go in. And I think, actually, it’s verging on, potentially even bringing in microbiome research into the picture. Because diet variation changes gut microbiota, and the microbiota are in some instances thought to be involved in generating olfactory signals that are used in mate choice. So there may be a mechanistic link there, through microbial responses to diet.

 

HS: You say that given our long history of diet analysis in ecology, there are many data sets that can be analyzed for niche variation. Has that been done?

DB: Not much. There’s been a little bit. I’m trying to remember the guy’s name. There was a Brazilian graduate student who worked with Laurie Vitt up in Oklahoma, who published a paper on lizards, basically using an old diet data set from lizards to look at latitudinal gradients in individual specialization. It was published in The American Naturalist as well. It had some unfortunate faults to it, namely, the way the diet data was collected. They misused the statistics to measure WIC/TNW. Well, I guess, calculating the point estimate is fine, but they then use our stochastic re-sampling process to generate key values for estimates. But because the diet data wasn’t collected as individual objects, that re-sampling didn’t have any meaning. So there’s been that.  I think Marcio Araujo had a paper that also looked at latitudinal gradients, synthesizing a bunch of data sets. But I think there’s a lot more to be done. A student could definitely spend a lot of time just synthesizing these data sets to generate estimates from lots of organisms.

 

HS: You say that individual specialization might be useful to study trade-offs, because you can eliminate the effect of independent evolutionary histories that are a problem when you do between-species studies. Have you seen examples of trade-off studies using within-species variation?

DB: Nothing comes to mind right away, but I hesitate to say No. I’m just not sure.

 

HS: Another interesting point you make is about the implications for conservation biology. You say that one thing that might be seen is that populations of individual specialists are more stable than generalists, and are more likely to adapt to environmental change. Have people looked at individual variation in the context of conservation and done such comparisons between specialists and generalists?

DB: Um, I think probably the best one in that regard was Deepa Agashe’s paper, also in The American Naturalist,  where she experimentally did this.  And I guess Jay Stachowicz’s lab and Randall Hughes have also done quite a bit on this, looking at, in this case, genetic variation in plants, establishing sea grasses, specifically establishing …I guess that’s not so much extinction risk as it is community diversity effects. But yeah, I think that this is where there’s been actually a fair amount of experimental field work and lab work showing that trait variation or genetic variation can have… it’s not uniformly stabilizing; it does depend a bit..  but I’d say, in general, it does seem to have reasonably beneficial effects that help sustain populations and improve up community diversity.

 

HS: You  also say that individual specialization could have non-adaptive causes, and that it would be interesting to look, particularly, at the role of introgression in increasing WIC or BIC.  Has there been more research on that?

DB: I can’t think of any off the top of my head. I mean, certainly, there’s a huge literature on the role of gene flow in constraining adaptive divergence, and implicit in that is the idea that gene flow increases phenotypic variation. But it’s not framed in that way, very often. You don’t typically see, in these migration-selection balance studies, you usually don’t see them talking about phenotypic variance per se. And that’s really where you would need to go and then trace that one step farther to the ecological variability.

 

HS: I wanted to ask you whether, in the 13 years since this paper was published, you have ever read the paper again. You already said that you haven’t, but have you at least gone back to it to look up certain sections, when you know, writing other stuff or when responding to questions from people?

DB: I think I have. It’s been a while. But yeah, I think I probably referred to the table a couple of times. Yeah, I have.

 

HS: Would you count this as one of your favourite pieces of work?

DB: Absolutely. Yeah. And I’d say it’s hard to know in advance. I think at the time, I didn’t have any inclination that it would be. I was happy with it, but I didn’t feel that it was going to be a defining feature of my career, which it certainly has been.

 

HS: What would you say to a student who is about to read this paper today? Would you guide his or her reading in any way? Would you suggest other papers they should read along with this? Would you add any caveats to the reading?

DB: I think after this conversation with you, I’d suggest that they spend some time thinking about opportunities – things that we raise in the paper, that really haven’t been pursued further, because, clearly, there’s quite a few of those.

 

HS: In terms of what we have learned since this paper, would you say that the main message of the paper is still true, in the way it’s framed here, and therefore it can still be read standalone?

DB: Yeah, I do think that is still true. I think that we know a lot more. In a sense, we wrote the paper to get people to pay attention to this subject, and I think people are paying attention to the subject now. And so, in that regard, it’s  maybe less important as a paper now, and maybe somebody would be better off reading a more updated version. But I still think that it lays out a lot of the core topics pretty well.

 

 

 

 

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