Reflections on Papers Past: Revisiting Janzen 1966

by Hari Sridhar

In 1966, Daniel Janzen published a paper in Evolution in which he synthesized his empirical work on different pairs of interacting ant and Acacia species in the neotropics, and discussed the possible origins and evolution of these mutualisms. Fifty years after the paper was published, I asked Dan Janzen about how he got interested in this system, his memories of field work and what we have learnt since about ants and Acacias.

Citation: Janzen, D. H. (1966). Coevolution of mutualism between ants and acacias in Central America. Evolution, 20(3), 249-275.

Date of interview: 23rd September 2016 (on Skype)

Hari Sridhar: I would like to start by asking you about your motivation to do the work presented in this paper, which formed part of your PhD dissertation. How did you get interested in this topic?

Dan Janzen: I guess it starts with my childhood. I grew up in Minnesota in the northern United States. When I was 14 years old, I saw a collection of tropical butterflies in the Minneapolis Public Natural History museum. I asked the curator, ‘Where did those come from?’ He said South America. Well, South America might as well have been on the moon from my standpoint, but I had heard of Mexico. When I went home, my father, by accident at the same time, said to me, ‘I have two months of federal leave and I will lose it if we don’t do something’. So I said lets go to Mexico and collect butterflies. That was 1952. It took four days to drive to the Mexican border, and we spent two months driving around Mexico, him seeing things, my mother seeing things and me collecting butterflies. I, sort of, fell in love with the tropics at that time. So when I got to graduate school in Berkeley in 1961, I said to my professor that I would like to go to Mexico to find a thesis project, something to do for a dissertation. And he said, ‘No, you are at the University of California and you will do it here in California. If you want to do it in Mexico you go to a Mexican university’. And I said, ‘No, I’m happy here at Berkeley, but I want to find it in Mexico’, and we had a big argument and it was agreed that I could go to Mexico for the summer of…I have to think backwards here..62.. yeah 1962, to collect insects for the California Insect Survey and look for a thesis project. So that’s how I was in Mexico in 1962 looking for a thesis project.

Well, I was just collecting insects of all kinds in Veracruz, and one day as I was walking across an old field, a beetle flew over my head and landed on a small shrub in front of me. And an ant ran after the beetle, trying to grab it, and the beetle then flew away. That sort of stuck in my head, and later on the same day I walked back by the same plant and looked closely at it. There were ants all over the surface of the plant. I thought that that was kind of curious and I noticed that the ants were going in and out of big thorns on the branches. I took one of these trees home to dissect and see what was inside the thorns and so on. So, I was looking at the ants like ants, without thinking about anything more. Well, maybe a week later I cut down two trees in a pasture, to take one of them home to dissect again. The other one, by accident, I just left there, by the stump. So there were two stumps about a metre apart, one with a tree cut down next to it and the other with no tree. About six weeks later, I walked by that pair of stumps and noticed that the stump that had no tree lying next to it had produced some sprouts but they were in terrible condition. They had been eaten down to almost nothing. Whereas the stump that had the cut down tree crown next to it had a beautiful one metre tall sprout growing out from it with beautiful leaves and very good condition and ants all over this sprout. Well, that caused me to realise suddenly that what I was looking at was an interaction where the ants were protecting the tree. It wasn’t just an accident that there were ants there. They were very involved with the tree. So I picked that up to study for my dissertation. And my dissertation basically consisted of removing the ants from thousands of these trees. In those days, the terminology was Acacia A-C-A-C-I-A. That’s been changed these days to Vachellia. It was basically removing the ants and showing what happens to the trees. Well, that of course revealed a very mutualistic co-evolved interaction between the ants and the plants. And in those days you were either an entomologist and thought about insects mostly, or you were a botanist and you thought mostly about plants. In the 60s very few people thought about the interaction between animals and plants. So this idea, and this example of coevolution, fell in the category of novel ideas to a lot of people, and so I kept right on studying it till I got my PhD and went on to my first job. That’s how I got started with the 1966 paper which is really just a description of the results of those experiments that I did in Veracruz, Mexico.

HS: That’s a fascinating story! I’m curious about a couple of details – do you remember the names of the beetle species and the ant species?

DJ: Well, the beetle was a chrysomelid. Family Chrysomelidae. It was a small red one, no, I never did determine the species of the beetle. But in tropical habitats like that there are a lot of species of Chrysomelidae. Hundreds of them. I have no idea which one of these it was but I do recall it was red. It was very visible. And it was flying in the day time. The ant is the ant that I ended up making the focus of my dissertation – Pseudomyrmex. In those days it was known as Pseudomyrmex ferruginea. Today it has had its name changed, there is still discussion about that, but we can call it Pseudomyrmex ferruginea. And the tree in those days was called Acacia cornigera. C-O-R-N-I-G-E-R-A cornigera.  Today it is called Vachellia cornigera; the genus name is changed.

HS: Who was your PhD supervisor?

DJ: My thesis advisor was – I had two of them – one was Herbert Baker – who is now deceased – in the botany department. And Ray Smith, who was in the entomology department. He is also deceased.

HS: On your website you describe your early research as somewhat like a “Victorian study of natural history”.  Give us a sense of what it was like doing field work at that time, especially in the context of this study.

DJ: After doing this study, I discovered that a mining engineer in Nicaragua, in Central America, had already described this interaction in the 1800s. We were talking Victorian times just now – he had described the same interaction the same time he was a mining engineer who had to ride on a mule from one mine to another mine to another mine, and mules are very slow. So it gives you a lot of time to see things along the way and of course he had seen the same thing that I saw. And he had described it in a book, and that book went back to Europe. He was European, and his name was Thomas Belt B-E-L-T. He described this, which then provoked a huge amount of armchair arguing in Europe in various languages – German, Italian, English, French, Belgian – as to whether the plant “needed” the ant or not. That was a very Victorian way of going at it. Somebody makes an observation often in a very distant land, nobody goes back to actually look and elaborate on that interaction but rather everybody sits around and argues about what it is. And that’s the kind of thing that, in 1960, was a very commonplace way of doing biology. The idea of doing experiments in the field with wild things was not a prominent way of doing biology in those days. In those days, you made observations, you wrote about your observations, you speculated about your observations and you went on. Today, we automatically think of doing experiments to tease apart what observations we have made, but back in the ‘60s that was not very common, especially in esoteric biological areas; obviously, in agriculture, experiments were the standard way of going at the world.

HS: Did you have people to help you with these experiments?

DJ: Well, in those days it was almost prohibited for a graduate student – a PhD graduate student – to have assistance. We were expected to do everything ourselves. And I certainly was operating that way. But one day, after being in the field in Veracruz for, I don’t know,  several months, I was standing in a pasture and a herd of goats went by me, and behind the herd of goats was a young man about 16 years old, 16 or 17 years old, taking care of the goats. He walked up to me, and the first thing I noticed was he was wearing a necklace he had put together of plastic rings, my plastic rings which I had used to mark individual trees! In other words, knowing nothing about me or what I was doing, he had come along found these plastic rings and had just collected them for fun and made a necklace for himself. So I tried to explain to him what I was doing, describing the ants and the Beltian bodies and the nectaries on the leaves and all those kinds of things. He stood there and listened to me and then walked off with his goats. About two hours later he comes back with his herd of goats and this time he has a branch of the Acacia in his hands and he asks me a whole lot of very intelligent questions about the ants and the branch. Now this was a Mexican farm kid who probably had never been through more than 3rd or 4th grade, I don’t know whether Cayo could even write. At that time, in those days, we didn’t even think about asking things like that. So, I looked at that and said ‘Wow, this guy is smart, I wonder if he could help me with my experiments’. I asked him where he lived and he pointed to a sticks and-thatch house upon the top of a hill. We went up there, I made arrangements to talk to his father on Sunday, and I came back and we had a long discussion. His father thought I was negotiating how much money he was going to have to pay me to take on his son as an apprentice, while I was trying to figure out how much I was going to have to pay him to hire his son to work for me. We ended up with a giant figure of 7 dollars a week. Cayo worked as my assistant the rest of the time in my thesis research. That was a very eye-opening experience because that taught me that among all these people out there working in the fields were just as many smart people as there were in the university. So ever since, we have always hired people directly from the fields, both men and women to help with our research in Costa Rica and other places. They are called parataxonomists; the word is derived from what you would call paralegal or paramedic. These are people who, often, never even get into high school, or if they do, they just finish high school and go to work in the field labour force. We have found that they are very high quality research assistants and can understand many complicated things and carry the work themselves as they would on their own farms. We specialise in doing this in Costa Rica but I learnt it from Cayo back there in Mexico in 1963-64.

HS: A lot of the data in this paper is from another publication, I think from the University of California…

DJ: No, University of Kansas is the big fat one. The University of Kansas science bulletin. That is the publication of my thesis.

HS: Was it always planned this way, that you would first do a big paper/thesis with all the data and then a conceptual paper?

DJ: Yes, once I had figured out what was going on with this particular ant and this particular plant, I looked at it in many species of ants and many species of plants and found this interaction going on in many of them. Of course that led me to think about what we call coevolution. I don’t know who invented the word “coevolution” as applied then; it was either me or Paul Ehrlich and Peter Raven, I really don’t know because we were all there, they were at Stanford and I was at Berkeley and we were all talking to each other all the time, and I don’t know where the word came up, but the conceptual paper on coevolution on ants and acacias is derived from those conversations. Coevolution today is just a normal thing. As soon as you start talking about it in animals and plants out there you realise there are many many examples where one species has evolutionarily reacted to another and then the other one has evolutionarily reacted to the first one and you go back and forth and back and forth and you find yourself with coevolution. That’s just the view today, a standard way of looking at the world. In 1962-63, that was a very novel way of looking at the world.

HS: You use two other terms in the paper – “ant-plants” and “plant-ants” – which are commonly used today. Were these terms also coined by you?

DJ: Well, I think the term ant-plant might be older, I really don’t know. That’s just such an obvious term for a person to use because there are so many species of plants around the tropics that have ants as mutualists. I would be surprised if some botanist has not described some of these plants as ant-plants before me. I probably came up with the phrase myself but I suspect many other people also have come up with the same phrase through just seeing the same thing. As far as ‘plant-ant’ is concerned, that perhaps is newer because the zoologists were not focussed on the plant-ant interaction. So that might be my phrase, entirely. But ant-plant, that phrase might be substantially older than me.

HS: At the time when you were doing this work, were there people, other than your thesis supervisors, with whom you were discussing your ideas?

DJ: No, I’m afraid not. I’m a very solitary person and there was nobody else in Mexico to talk to about this. You have got to remember – I just started with a visible interaction in the field that anybody could see. What I learnt from that, I learnt by watching it; not by talking to people. I’ve spent my whole life understanding biology that way, seeing it first in the field and then later on, it becomes formal, it develops a vocabulary, it becomes something you talk to other people about. But no, in general, my ideas don’t come from talking to other people.

HS: You acknowledge a few people in your paper. If you don’t mind, could we go over the list to learn a little more about how they helped?

DJ: Sure.

HS: You say “Throughout this study, I have been aided and inspired by the comments and assistance of E.O. Wilson”..

DJ: Yes, that’s the E.O. Wilson you know. He was a beginning professor at Harvard University. He came to Berkeley and tried to convince me to go to move to Harvard as a graduate student. This was after I had figured out this interaction. I knew nothing about ants, so I went to him to learn about ant taxonomy and what the classical ant people know, very early on. But that was after I had gotten focused on this ant-plant interaction.  He gave me a second copy he had of a very useful old book on ants and what the ant-people thought about them.

HS: And then you thank W.L. Brown..

DJ: Yeah, that was Bill Brown at Cornell. He was another ant biologist who, also, I went to for the same purpose, to learn about ant biology. I should explain here – my way of doing science is to see some interaction in the wild, in the field, that involves a plant, that involves an animal. Usually, I don’t know anything about the plant or the animal. All I see is what they are doing in the field. Then I ask myself who in the world knows a great deal about this animal. I go to that person and ask them to explain what they know about this animal. Then I say – who knows about this plant and then I go to that person and ask them to explain to me a lot of what’s known about the plant. My job is to put the two together. Brown is deceased as well.

HS: And then there is V.E. Rudd..

DJ: She was a plant taxonomist at the Smithsonian institution. She was sort of the world authority on Acacia. I took my plants to her to make sure we had the names right. She is the one who gave me the names for these plants.

HS: And then C.D. Michener..

DJ: He was the person who employed me, the first time at the University of Kansas, my first job. And he is the person who convinced me that there was a bigger audience out there that could be interested in this and that I should aim my discussions and descriptions of the interactions to that bigger audience. I started out looking very narrowly at ants and plants and insects. I was not thinking about people. I would never think about somebody like yourself who would read the paper. I didn’t think about who would be paying attention to this. But Michener was a young professor at the University of Kansas and very focussed on trying to understand how insect societies work and then how to transmit that information to a much bigger audience.   He is now deceased.

HS: H.V. Daly

DJ: Daly? That came about because halfway through my thesis research in the field, Ray Smith, my advisor at that time in the Entomology Department, wrote me a note, a letter, in Mexico saying that he thought we should co-author my thesis.  I wrote him back and said,  ‘well, since you didn’t do anything, you had nothing to do with my thesis, I do not think you should be a co-author’, at which time he threw me out of the Entomology Department. Howard Daly was a young professor in the Entomology Department who saw this happen and, without me knowing it, went to the administration and took me back. So when I came back from the field after being gone for a year I was still in the Entomology Department, but now I had Hal Daly as my major professor.

HS: You also thank The Evolutionists’ Club at the University of Kansas

DJ: Yes, that’s because I discussed the stuff with them.

HS: And finally you also thank G.L. Stebbins for comments on the manuscript

DJ: Yes, he was a very well-known plant ecologist in California who…let’s see, how did it work.. what happened was, because the Entomology Department in Berkeley did not like me, I was not allowed to give my thesis defence in the entomology department. So Stanford, across the bay, invited me to give my thesis defence there. When I went to Stanford and gave my thesis defence, at the back of the room was an old man with his head down on the desk who seemed to be sleeping through the whole thing. We get to the end and he raises his hand and he says ‘Your ants are like the chemicals in my plants’ and at that point the light bulb went off in my head, which should have gone off much earlier, that the ants are the same as secondary compounds in plants, the things that give plants flavours and drugs and all those things. The plant is investing in the ants and supporting the ant colony instead of making chemicals inside of itself for defence. Stebbins was a plant ecologist, he didn’t know anything about insects, but when he heard me talk he realised that my ants were the equivalent of nicotine or morphine or opium or caffeine. I thank him here in recognising this that was a major contribution to my thinking process.

HS: I wanted to ask you something related to what you just said. In the paper you say that the taste of the leaves of this plant is not as bitter as other Acacias, and that the sting of the ants is much worse than other ants.

DJ: That’s right. If you remove the ants, it’s like going to an opium poppy and removing all the morphine. Then everybody comes and eats it.

HS: I was also curious about this sentence in the acknowledgements.  You say “The following people have read the manuscript and offer helpful criticisms but I do not mean to imply that they necessarily agree with all of the conclusions in the final draft.” Was there a particular reason why you wrote that?

DJ: I don’t remember (laughs), it was a long time ago. I don’t remember. Probably because there were still people who were not convinced and I did not want to insult them. No, but I don’t know. I shouldn’t speculate. That was too far back I can’t remember.

HS: Do you remember how long you took to write this paper and where and when you wrote it?

DJ: Well, let’s see, yeah I think I can do a lot of that. There are two different things here. One is my thesis. That has a different history. In the fall of 1962, I started writing my thesis. I got through about hundred pages and decided that all this was based on what I’d seen mostly in the field and a few early experiments. So I took those 100 pages and threw them away. And I went back to Mexico in late 1962 and spent six months in the field. Then I came back to Berkeley for a short time, went to Costa Rica for a couple of months, came back again and I then continued writing up through December of ‘64. So it was about two years producing the big fat thick document from the University of Kansas science bulletin, which is my whole thesis. The individual papers that came out of that, including the short one that you are referring to, those things were only a matter of a few days. The real work was in doing my thesis experiments and having this story firmly in my head. Once that was done then writing the papers was easy.

HS: So you wrote the papers after you had written the thesis?

DJ: Yes. Remember, in those days the most important thing to get done was the thesis. Not writing papers for journals. Papers for journals were sort of an extra. The thesis was the hard thing. Once you got that done, some of us then wrote a lot of papers about the content of the thesis, but many other people never did at all, so all they have is a thesis somewhere in a library. This business today of publishing papers as chapters of your thesis, at the time or even before you get your degree, was not done in the 60s. In fact, there were even arguments that if you published a chapter it could not be included in your thesis.

HS: How did you decide to send this paper to Evolution?

DJ: Well, because it was about evolution! (laughs). That’s all. You know, all this business today of trying to figure out what’s the best journal to put your paper in, that didn’t exist in the 60s.

HS: You didn’t consider any other journal?

DJ: Right.

HS: Did it sail through peer-review?

DJ: Yes, in those days, a paper like that in Evolution that was backed up by so much experimental work was a novelty. It sailed right through, yes.

HS: Earlier, you mentioned the controversy and debate that Belt’s observation provoked. Was there similar interest when this paper was published?

DJ: No, not really, because the primary person who was a driver for lot of that doubt about whether the plants needed the ants had died. He was William Morton Wheeler, a professor at Harvard University, who was firmly convinced that the plants had no need for the ants. The ants meant nothing to the plant, that was his viewpoint. And he was a very very dominant figure in ant biology in the world. But when he died, there was no longer anybody who was interested in defending that and the experiments that I did in Veracruz made it very clear that the plants needed the ants. So there was no argument about that. The big controversy was prior to that, in Europe, when Thomas Belt wrote his book about things he had seen in the Central America and included this, a little chapter on it, in his book. That did not sit well with the European armchair scientists. Also, many people in those days were still very religious, and so the idea of evolution being important in fashioning what’s going on in the world was not welcome. In fact, I learnt later that, Wheeler, who was the one who felt that ants were not important to the plant, was a very devoutly religious person, and the idea that all this evolved was not a welcome thing to him.

HS: This paper came out in the early phase of your career, and went on to become really important in the field. Did it have a strong impact on the trajectory of your career?

DJ: No, I don’t think so. Because..I won’t say I was bored with it.. but, very quickly, I moved onto a second area of study . I work in many different areas, I’m not fond of making one study, becoming famous and talking about that for the next 25 years. I’m much more inclined to see a story and develop it and write it up and move on to another story. And that’s what happened in this case as well, because the world of animal-plant interactions is full of very interesting interactions. The ants and the plants was one, but it was very comfortable for me to move on to other animal-plant interactions afterwards. So, my career was based on being an ecologist of animal-plant interactions on the one hand, and second, on working heavily in the field in Latin America rather than in a laboratory in a more northern place.

HS: Did you continue to work in this field site after this study?

DJ: Not at all. It’s all sugarcane. It’s all destroyed long ago. All destroyed. That’s the fate of most areas where you work in the tropics. You find them to be good spots or something at one time and 10 years later they don’t exist.

HS: Did you visit the site after the study?

DJ: Yeah, I’ve been there several times over the last 30-40 years but there’s no point in visiting. As I said, it’s all sugarcane now.

HS: In the paper, you show a photo of an Acacia and say it’s in a really disturbed site. Were these plants typically found in disturbed sites?

DJ: Okay, there are 15 species of these ant-acacias. There are no humans in this system. They live on the edge between very dry circumstances, almost desert circumstances, and dry forest. Dry forest is the kind of forest that used to occur all through central India, – doesn’t anymore, there are a few tiny patches – think of that kind of dry forest. In the rainy season it is very shady under the trees and all that. Next to open areas – they are open because they are very dry – the ant-acacias do very well on that interface zone between the two. Now when people move in they put in roads, they put in fields, they put in pastures, they put in towns, they make a lot of edge and the acacias grow very well in those edges and so that’s where everybody sees them. But if you have a national park or some place that’s not disturbed, they are very rare and they occur only on edges between, where they get enough light, because they are quite resistant to being dried out. They do need water in the rainy season, but they also need a lot of light and so they get that light by being on the edge.

HS: You say that the photo you show in the paper was taken in Nicaragua. I was curious why you chose to use this photo instead of one taken at your field site.

DJ: Well, the interaction extends from north-central Mexico all the way to Colombia. In 1965-66-67 I drove all the roads from northern Mexico to the Panama canal and then flew over to Colombia as well mapping the distributions of the ant-acacias; to know where they are. And so I just used photographs that were easy for me to use; that I happened to have. It didn’t matter to me where the photograph was taken because the interaction between the plant and the ant is the same in Mexico, Nicaragua, Honduras, Panama, Costa Rica, Colombia; it’s all the same interaction. Different species of Acacias, different species of ants but it’s the same interaction.

HS: It is now 50 years since the paper was published. Would you say that its main conclusions still hold true, more-or-less?

DJ: Oh sure, sure, oh yeah, because I’m just describing a process that’s been going on for probably a million years. And I think it escaped attention mostly because it was about the interaction between an animal and a plant. I think it’s maybe hard for you to realise that, up until the ‘60s, animal people studied animals and plant people studied plants. Very few people tried to study the interactions between them because you had to learn two different worlds. Remember, we used to have botany departments and entomology departments and zoology departments. Three separate administrative castles. Each one of them with their own purpose, their own rules and own awards, their own students, their own budgets. When I was in the entomology department, it was viewed as not good if I went to seminars in the botany department!

HS: If you were to redo this study today, would you change anything?

DJ: I would take more photographs! No, I think I would do the study the same way. One of the characteristics of this study is that, I picked out a spot where there were a lot of Acacias growing and for 20 of them I cut them down and removed the ant colony and for another 20 I cut down and left the ant colony there. So, I had a control and an experiment. And I repeated that about 60 times, in different places – very wet spots, very dry spots; deep shade, full sun; early succession, late succession –  many different kinds of conditions. And people say – wow, that was overkill, that was way more than you needed to do, but what people don’t realise is that when you set up field experiments, all kinds of bad things happen to them, if they are not controlled. There are a whole lot of ways in which we lose…I lost almost 50% of my plots to accidents of one kind or another – the owner of the field site changed their mind, there was a storm, there was too much rain, the city decided to put a water pipeline through the middle of my plot! I mean all kinds of things; I lost a lot. If I was advising a student today about doing this kind of fieldwork research I would advise them to set up a lot of plots and anticipate that a big number of them – 50% of them  – are going to be destroyed over the next two years. That was what I did, by accident more than on purpose, but today I would do it more deliberately.

HS: You said you stopped working on this system soon after this study. It looks like the last paper by you on this topic was in the early 70s. Do you still follow the research on this system?

DJ: Yeah, it’s very easy to do that in today’s internet world of course. I have no trouble finding the papers because they are always labelled with the names of the plants and the ants. So I keep up by reading them. Also, remember these things grow in my front yard in Costa Rica. They are right there staring me in my face all the time. And they are very useful for explaining coevolution and explaining ecology to visitors as real things, not ideas on a blackboard. Not slides on a PowerPoint, but just there it is, right there! You can stand there two feet from it and understand it. And the ants don’t run away. You can go and have a look at them, any time of the day or night. They are very easy to find for a new person. Once you show them one, they go off and find more by themselves. It’s a very convenient interaction.

HS: This paper has had a huge impact on the field, but at the time when you were doing this work, did you, in any way, anticipate its influence?

DJ: I’m afraid that you are not understanding that, in those days, no one thought about that. A little bit of context here. In 1964, my advisor said to me, ‘What kind of job are you planning to go to?’ And I turned around and said, ‘Why, I have no idea’. We didn’t even think about it. I just assumed I would be a professor somewhere. Then he said to me,  ‘Well, there are two jobs opening up that I know of, one in Cornell and one at the University of Kansas. Would you like to interview?’ And I said, ‘Well, I guess so’. Two of us – one, a big fellow named Dick Root, who is now deceased and I went and interviewed for the two of them. We met each other on the street at Berkeley afterwards. And Root said to me, ‘Well, which one do you like?’ And I said, ‘Well, I like KU – University of Kansas – because it is a little more academic’, and Root said, ‘Well I like Cornell because it is a little more agricultural’. And so I said, ‘OK, Dick you take the one at Cornell, I will take the one in Kansas’; that was it. That was competition. There was not even a job advertisement in Science or anywhere. In those circumstances, you didn’t think about – Will this paper get me a job? Will this paper make me famous? Will this paper be job security over the next 20 years? I wrote the paper because I was curious and I liked explaining it to other people.

HS: Yes, it is difficult for me to imagine the academic world of the 60s.

DJ: Yes, all these people you mentioned – E.O. Wilson, others, Bill Brown, there were another 5-10 of them – we all knew each other, because we were the only people in the United States working on these things!

HS: Have you ever read this paper after it was published?

DJ: No, I don’t need to do that. The concepts are so simple, the idea is so simple. I give a lecture on it every single year, because it’s in my ecology course I teach here in my university. I’m still using the same slides that I used in 1965.

HS: It will be nice to include one of those slides as an image in the interview.

DJ: Sure. It’s on the website. My course is all on the web for anybody and the whole lecture is right there. I’ll send you the link to the course website, and you can download an image from that yourself if you want.

HS: Is this one of your favourite papers, among those you have published?

DJ: No, I don’t think so. I think it’s one that is very well known but I don’t think the intellectual content is particularly difficult or striking or revealing, because I was simply describing something that was going on, obviously, in nature. Very straightforward. Anybody can understand it; every school child understands it in two minutes. There are other things that are more complicated and have had a bigger, I think, overall impact.

HS: Give me some examples.

DJ: An easy one is one that’s called “Why fruits rot, meat spoils and bread moulds”. That’s in American Naturalist and basically pointing out that these things which we call rotting and spoiling and moulding are in fact the microbial world altering the food item so they get it instead of me. That’s one. The other one is called “Why mountain passes are higher in the tropics”.

HS: What would you say to a student who is about to read this paper today? What should he or she take away from this paper published fifty years ago?

DJ: Oh, I’ll let them take away what they want to. My students in my class do read it. It is one of the papers that they read, but I let them take away what they want to take away. I have a different teaching philosophy – what I believe in is putting the information out there and you can take what is useful to you.

HS: Could you tell us a little more about how you use this paper in your class?

DJ: They read the paper, they look at the slides, which I will send you the website for, and its simply telling the story and explaining the concept of coevolution, a concept which is very easy for people on the street to understand because it’s just like an arms race between, say,  Russia and the United States.

HS: When you compare this paper to the ones you write today, do you notice any striking differences?

DJ: Yes, in one respect. In 1985, which is quite a while back, I had an experience that told me, as I said to a very large audience at that time, I can go on writing papers like these for the next 30 years and produce just as much literature, and I would turn around and all the organisms would be gone. Gone. Extinct, turned into rice fields and sugarcane fields. So, in view of that, I have to basically stop doing these kinds of papers. And focus on keeping the organisms alive, about which we write. So, my papers today, since 1985, have mostly been focussed on some aspect of that. It gets into government and politics, it gets into motivations of people, it gets into why we are better off by keeping some chunks of the world wild. Stuff that you would generally categorise as conservation, in one sense or another, or what I call biodiversity development. The focus in these papers is not so much something that the academic community gets all excited about. Often, it’s about things that are already obvious to the academic community, but the academic community is cloistered in their ivory tower and not reaching out to the rest of the world.

Author Biography: Hari Sridhar is a post-doctoral researcher studying heterospecific sociality at the Centre for Ecological Sciences, Indian Institute of Science, Bangalore. Since early 2016, he has been interviewing authors of well-known papers in ecology and evolution, to find out about: 1. the making of the paper 2. the impact the paper had on the author’s career and research and 3. the author’s current stand on what was said in the paper. Through these interviews, Hari wants to construct ‘shadow papers’, which capture the past and future of the original published articles. His interviews are archived at

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