Evolution Enclaves: Darwin the Botanist and Origins of Life Research
David Kohn, curator of the Darwin's Garden exhibit at the New York Botanical Garden, discusses Darwin's botanical studies. And Harvard Medical School's Jack Szostak talks about research into the origins of life. Plus we'll test your knowledge of some recent science in the news. Websites mentioned on this episode include www.nybg.org/darwin; www.hhmi.org; www.sciam.com/daily
Steve: Welcome to Science Talk, the weekly podcast of Scientific American for the seven days starting May 7th, 2008. I'm Steve Mirsky. This week on the podcast: some of the less discussed aspects of evolution. Darwin as a botanist with David Kohn, curator of an exhibit on that subject at the New York Botanical Garden and Origins of Life Research with Harvard Medical School's Jack Szostak. Plus, we'll test your knowledge about some recent science in the news. The Darwin's garden exhibit at the New York Botanical Garden looks at Darwin's work as a botanist as well as offering a walking tour of evolutionary science with botanical examples. David Kohn recently retired from Drew University as professor of science and society emeritus and is now the general editor of the Darwin Digital Library of Evolution based at the American Museum of Natural History. We spoke on April 23rd at the Garden.
Steve: Dr. Kohn, good to talk to you. We're sitting here in the rare book room at the Botanical Garden and it's really great to be in this room.
Kohn: It's wonderful to see you here.
Steve: We are surrounded by some original Darwin publications, and if I think of Darwin, I think of finches and Galapagos tortoises, which really didn't play much of a role,
but [and] he looked at the shells—but I never think of plants.
Kohn: That absolutely shocks me, you see. Well, actually plants are a continuous part of Darwin's life from childhood through maturity. You know, as a child he played in his father's garden, which is a major garden. He came from a family of, I would say, the horticultural and botanical intelligentsia of England in the 18th century and early 19th century. His grandfather, Erasmus Darwin, who was one of the earliest evolutionists, also was a major populist of Linnaeus, the great botanist.
Steve: And his father?
Kohn: His father was a doctor who had a great garden, and so Darwin, it's in his blood. I think of him as to the greenhouse born.
Steve: That's pretty good.
Kohn: On the other side too, on his mother's side, his mother was Wedgwood. His uncle was one of the founders of the Royal Horticultural Society and a major supporter of horticulture and botany. His grandfather writes a book called the Botanic Garden.
Steve: What exactly was Darwin's botany in relation to his formulation of evolution?
Kohn: It's integral to his view of life, and plants are part of life and Darwin's view is that all life is knitted together. So, he is interested in plants in that general way. His education in botany, which I think is pretty well has been underappreciated, was maybe his longest formal education in any subject. He took his course when he was in Cambridge University, albeit
was a three- to five-week course, but took it three times in a row, three years at[in] a row. So, almost the entire time that he was in Cambridge, he was studying botany, which involved field trips, dissection of live plants. We know actually what he probably was taught by Professor Henslow because we still have his syllabi. We know that he had a good basic grounding in botany. When he was on the Beagle, one of the objectives he had was he got the, you know, mission of collecting natural history specimens; it's rather open, what he has to do, he really does what he wants, but he does manage to collect over 2,000 plants. So one of the dimensions of Darwin as a botanist is [as] a natural history collector. He collects plants that are unique; he has got a very good eye. He follows his professor's instruction to collect everything in flower when he is particularly interested in the area. So, the same time that he is collecting the famous fossils, the giant mammal fossils, the megafauna, which is another thing that Darwin is famous for. These big sloths and animals that are extinct obviously, but they are represented still in South American fauna and they were a big find. In fact, that may be what got Darwin's career going. At the same time that he is making these discoveries, or you know excavations of bones, he is collecting all the plants in the area, and went to the Galápagos and there he specifically collected everything he could find, if that had a flower on it, which I think was an instruction from Henslow. So, that his collection is the basis for our understanding of the Galapagos flora. I think that perhaps we now have four to five as a rough estimate, four to five times more plants than Darwin collected, but that's not bad for three weeks. That's just a beginning. Now he is a collector of plants, he is anork that is bota observer of plants, very careful observer, an experimenter on plants, and a theorist, you know, functional meanings of different plant structures. So there is an enormous amount of volume of wnical that Darwin produces. He writes six books on plants. It is fair to say that from the time The Origin of Species was published in 1859 till his death, the original research that Darwin does—that is with his own two hands and eyes—is botanical. He does other work, but it's more, you know, literature based. The original stuff is botanical and then in the making of The Origin, you know, [the] making of his theory, plants are interwoven with other organisms, obviously something— you know, he would take as examples where they are important, but there are certain botanical issues that are of key importance and one of them has to do with reproduction. The plants [were] have really fundamental for his grasp of the laws of reproduction, and it's the evolutionary consequences of reproduction.
Steve: The flowers of plants are particularly important to Darwin.
Steve: It's the most obvious place that evolution acts on a plant perhaps. And then the other side of it is, well you refer[ed] to it
to me earlier before we started to record, as an organ of evolution. What did you mean by that?
Kohn: Well, what I mean is that our common understanding today, the flower is involved in reproduction and involves pollen traveling from one plant to another often brought by a pollinator like you know, an insect, a butterfly or a bee and that is an organ. If you'd ask anybody what does the flower do? Well it produces seed, but it does it by crossing between plants. I think that's the general common sense understanding of plants; and that was not the case when Darwin started because most flowering plants have got males and females in the same flower. It was assumed back in the 18th century, when people first realized—like Linnaeus and others—that plants have sex at all, male and female sex, it was assumed that the real function was to produce offspring, that is seeds, and that since they were both there, the plants fertilized itself. Darwin came along and thinking this through from first evolutionary principles saw that that is an impossibility to be the function of a flower because if they self-pollinated perpetually that would mean there ultimately would be no variation, that would be a way to make clones. He figured this out, focused on this in 1839 in notebook E—his E notebook, one of his transmutation notebooks—so it's part of his early evolutionary thinking and it's one of the first applications of natural selection. Right after he discovers natural selection, he starts thinking about this problem: Why is that? Natural selection requires variation to work. It is selection among different hereditary variants, right? So, now if you have a group of organisms, variation is reduced; well, no evolution. This is the way that Darwin thinks. "Is there a problem for my theory?" If there is a problem, he'll do his best to try to solve it. And the plants were potentially a major problem; it's one of the big major problems that Darwin felt that he had to solve and it forces him to think, on this evolutionary basis, that there must be some other purpose. And the purpose is, for a function, I should say, and the function is the flower which has all its attractive parts, its—in fact its beauty is really involved, you know, generally in attracting insect or other animal pollinators to guarantee outcrossing. You know, Darwin lived in an age when people were beginning to be worried about inbreeding depression, as you might call it, in general, in humans; he himself is ...
Steve: He married his second cousin.
Kohn: He married a cousin, yes, and [that] could be a concern. In fact, this thinking is happening just after he gets married.
Steve: Right; anybody who watched the monarchies in Europe, they are all a relation in one or the other side.
Kohn: Yes, okay, well, if you think about it, if you marry your cousin, you're not doing anything dangerous compared to what a flower would do, right? Because it is marrying itself. The degree of inbreeding is much steeper. It would lead to deaths in many fewer generations. So I think the biology here, at least, is much as a cultural context, if not more [reason] for him to be interested in this. It's one of those interesting intersections between—that he is marrying this woman in Wedgwood who is his cousin [at the same time] that he is thinking about inbreeding.
Steve: Actually, I think she was his first cousin.
Kohn: I think she was his first cousin, but one thing that I am really bad at his lineages. (laughs)
Steve: His work with plants enabled him to make some predictions that turned out to be correct.
Kohn: Yeah. So he gets these exotic plants—and in some cases nobody has seen the pollinator—but he is able to predict what the pollinator is like just by looking at the structure of the plant; and this, in a way, is kind of [an] independent test of his theory and a very amusing one and is one that will also get him a lot of pleasure.
And in general his plant observation is jus other; The one that is most famous is the star, or comet orchid. It has a 12-inch long nectary—there is a tube where the nectar accumulates—and he predicts that there is a moth, thinks it has to be [a] moth with a very long proboscis basically like a straw that would be, maybe 11 inches long. And some time later this moth is discovered in Madagascar. This is an interesting thing about Darwin's botany, you know, is it that Darwin is interested in botany because he is an observer, because he is a very observant person. Or is it more or less like the victory of empiricism or is it something else, and I think it is something else exactly. I think it is the fact that Darwin is operating from this theory of evolution that has a sub-theory about the necessity of outcrossing that leads him. When he looks at a flower, he knows exactly where to go and to then make the careful observations. So it is observation, very, very carefully guided by theory. So there is a kind of blend of the empirical and the theoretical.
Steve: The Darwin's Garden exhibit runs until June 15th, so if you're in the New York City area, check it out. Go to http://www.nybg.org for more info, hit the link for the shop and then for books to find info about a monograph by David Kohn about Darwin and botany. On May 6th, philosopher[s] of science Michael Ruse and Kohn were part of the discussion on Darwin at the New York Botanical Garden. Here, they answer a question about whether Darwin ever addressed the origin of life.
Ruse: That's a fascinating question and it throws so much light on The Origin and Darwin. I was referred to it in terms of the Sherlock Holmes story, "The Dog That Didn't Bark in the Night". Why didn't Darwin talk about the origin of life in the Origin? Because everybody else who wrote on the subject did. If you look at Lamarck it is there, I mean, they all do [it]; and afterwards people like
Heckel [Hegel], it's there; and I think that this really does show not just that Darwin was clever, but that he was a sophisticated thinker and he knew that getting into that one was just going to, you know, for another matter, open a can of worms. And very cleverly he just stays right away from it, one or a few forms, and leaves it like that, and if you look then at the torrent of stuff which is written about The Origin afterwards, it's clear that that was a very good strategy to take; because by and large that's not what people are on to. I mean, they are all on to other things, they are all on to man, I mean that's what they are all interested in including Darwin, of course. But the origin of life by and large doesn't brew up as a real problem for Darwin.
Kohn: He was always trying to defend, you know, make the target, the religious target he is wearing on his back as small as possible; and of course it's gigantic, but that would have made it, you know, just enormous, because he can't say a word scientifically at that point in 1859 that has any scientific justification, unfortunately. He does merely speculate and he does try to avoid that.
Steve: Which leads us right to Jack Szostak; he is in the genetics department at Harvard Med School and is a Howard Hughes Medical Institute investigator and he actually studies origins of life. We spoke on May 2nd at an evolution conference at Rockefeller University in New York City.
Steve: What exactly does somebody who is studying origins of life do that a regular old evolutionary biologist does not do when they are doing their research?
Szostak: Well, what we're really trying to understand his how molecules can get together and start to act in a Darwinian fashion, so we're talking about the origin of cellular systems that can evolve, which is completely different from the way the chemicals interact with each other.
Steve: How is it different?
Szostak: Well, chemical reactions are, you know, controlled by the thermodynamics of chemistry by kinetic considerations, but Darwinian evolution is completely different because in our case we are talking about populations with variation and the selection of variants that are more fit, and it's that['s]
it's repeated and repeated; then better variants come to dominate the population. We just don't have that kind of cyclic feedback system in a simple chemical reaction.
Steve: So, where are we in this kind of research? I mean, obviously no one has created a living cell from buying reagent grade chemicals, so where does the research stand right now?
Szostak: Well that's basically what we're trying to do, but it is obviously going to be a long process. The way we're thinking about it, the critical components that we have to think about, are some kind of genetic material. So it could be RNA or DNA like we have in modern biology or it could be some related kind of material; and we are also thinking about some kind of cell envelope or cell membrane—not that that's necessarily the very first way Darwinian systems began, but at some point they had to transition into a system more related to modern biology where cells are all bounded by membranes—so we're thinking about how to assemble these two components and get them to interact with each other.
Steve: That's an important point—should you succeed, that doesn't necessarily mean that that's the way it happened, it's just a, sort of, a proof of concept, right?
Szostak: Absolutely! I mean what we're interested in is figuring out plausible pathways for the origin of life. It would be great to have even one complete plausible pathway. But what we find often is when we figure out how one little step might have worked, it gives us ideas, and then we end up with ultimately two or three or more different ways in which a particular step could have happened. So that makes us think of the overall process may be more robust. So, you know, ultimately it would be nice, I think, if it turned out that there were multiple plausible pathways then of course we might never know what really happened on the early Earth.
Steve: And it should also be noted that this is a pretty young field, so it's—some people who don't want you to succeed point out that no scientist has been able to prove this
off yet, but [that's] not really surprising; it is a complicated thing and people haven't been working on it all that long.
Szostak: Yeah, I think, you know, in some ways the field can be dated to the, you know, early experiments of Stanley Miller about 50 years ago. So it's a long process going from very small simple molecules up to a cellular structure. They are parts of a pathway that I think are getting to be well understood, but there are many gaps in our understanding. But just because there are parts that we don't understand doesn't mean that we will never understand.
Steve: You gave a talk yesterday, you talked about some of the simple and yet unexpected phenomena that you see as you are doing this research. Can you talk a little bit about that?
Szostak: Yeah, sure. I think one of the interesting things about approaching this problem—they are actually trying to a build system—is that you come across all kinds of unexpected interesting phenomena. And I think it is really nice, a sort of, broadening our perspective, making us think about different simple physical processes, different things that membranes can do, different ways, you know, the environment can impact the assembly processes. There's a lot of surprising stuff
at [out] there once you really start to investigate the system in detail.
Steve: Can you talk about any other specifics there?
Szostak: Like I mentioned some of the things that have been published, for example, a few years ago, we were starting to look at the way that membranes self-assemble—and these are not modern kinds of membranes, these are membranes made with fatty acids. And it turns out that the assembly of membranes is actually catalyzed by preformed membranes, that's a surface phenomenon and it is generalized and many different surfaces will catalyze membrane assembly. And one of the interesting ones is [that] the clay minerals will help membranes to assemble; so it turns out there is a very common clay mineral that it previously had been looked out by prebiotic chemists and shown to help RNA molecules to assemble. So ultimately what we had was a simple common mineral that can help genetic material to assemble, can help membranes to assemble and it turned out can help bring them together. So that was a very satisfying outcome, but you know it has turned out there are many other unanticipated simple physical processes that have been found in the course of these kinds of experiments as well. Well, one of the issues that we have to think about is how small molecules can get across membranes without all the complicated modern biological machinery that controls the transport of molecules across membranes. So, we were starting to look at how simple molecules like sugars get across these fatty acid membranes, you know, spontaneously without any help from fancy proteins. And it turned out completely unexpectedly that ribose, which is one of the building blocks of RNA, gets across a wide range of membranes much more quickly than a set of very closely related sugars. So, it makes you think that, well, maybe that could have been one contributing factor to why we actually use genetic materials that incorporate ribose because early cells that relied on an external source of ribose would have had easier access to that material compared to competing the cells that were looking for the different sugar that had a harder time getting across the membrane. Now we still don't really understand why ribose gets across so much faster; we have some ideas but that's just a topic that's going to take a lot more study, but we never would have found this surprising result, you know, if we weren't systematically looking at these kinds of transport processes.
Steve: So if you want to make new RNA, if you're duplicating RNA within that membrane, the fact that you can bring ribose into the protocell easily is a real advantage there?
Szostak: Yeah, that would become an advantage at the point where the early steps of metabolism started to evolve.
Steve: So where do you think you're going to be in—or the whole field is going to be in—you know, this is the typical hackney journalist question, but where do you see yourself in 10 years?
Szostak: Well, the progress over the last 10 or 20 years has been on the one hand very encouraging that we have learned a tremendous amount; on the other hand we have also learned that there are things we don't understand that we hadn't even thought about before, so you know I can't really say that, you know, we will have built a cell in three years or 10 years or 20 years; and we don't even know all the problems yet, but I think the relevant part is that there are lot of really interesting scientific questions that are easy to investigate; there is a lot of interesting stuff that we are going to find out, so I think it is just going to continue to be an exciting time.
Steve: What is one of the things that you didn't realize you'd need to know that you now know that you need know?
Szostak: Well, it is looking like one of the aspects that may take us some time to figure out—how to get a self-replicating genetic system off the ground. And when I started off in this field, about 20 years ago, I was pretty confident that it would be something we could do relatively [easily], these early events in [an] RNA catalyzed replication system, and that's turned out to be substantially more difficult than I thought.
Steve: Where RNA pretty much catalyzes its own reproduction?
Szostak: Right. So there has been tremendous progress in that; we have certain proof of principle ribosomes that are RNA dependent, RNA polymerases, which is great, but I think we really have to step back and think about the problem in a different way in order to develop a simple, effective system that can actually do self-replication and not just be a proof of principle. So that made us look again at the chemistry of replication and start to explore a wider range of nucleic acids.
Steve: For more, go to the Howard Hughes Medical Institute site, http://www.hhmi.org, and search for Szostak, that's s-z-o-s-t-a-k. See a specialty article "Evolution is Our Laboratory".
Now it is time to play TOTALL....... Y BOGUS. Here are four science stories; only three are true. See if you know which story is TOTALL....... Y BOGUS.
Story number 1: Belly fat is associated with increased risk for type 2 diabetes, but fat elsewhere in the body may lessen the risk.
Story number 2: More fat news; the number of fat cells you have remains constant after childhood.
Story number 3: Some bats are capable of producing sounds 100 times louder than a rock concert.
And story number 4: Ben Stein, the star of the antievolution movie Expelled is a big supporter of most other science in general.
We'll be back with the answer, but first I want to tell you about Scientific American's Daily Digest, a new e-mail newsletter from the editors of Scientific American, which includes me, but don't let that stop you. In Scientific American's Daily Digest, the editors highlight the latest news, articles, podcasts, and videos from www.SciAm.com and deliver it to your inbox five days a week, so you get breaking news, thought provoking features, selected blog posts, links to podcasts and slideshows, updates on magazine articles, and more. So you won't miss anything at SciAm.com ever again. Just sign up at http://www.SciAm.com/daily.
Meanwhile, back at the quiz. Story number 1 is true. Body fat that is not belly fat may actually lessen the risk of diabetes. That's according to research in the May issue of the journal Cell Metabolism. Fat in the hips and thighs is associated with improved insulin sensitivity which is lacking in diabetes. The researchers hope they can find whatever substance the fat is making that might help glucose metabolism.
Story number 2 is true. Your fat cell number does remain constant, but new fat cells arise and replace older ones that die off to keep the number constant. Researchers hope that by understanding that mechanism, they might interfere with it leaving you with fewer fat cells. For more check out the May 6th daily podcast, 60-Second Science.
And story number 3 is true. Some bats can screech 100 times louder than rock concerts. That finding appeared in the journal, Public Library of Science One. Bat calls had previously been recorded at 120 decibels, but researchers found bats in Panama that are much louder. They say that the bat makes a noise equivalent to standing on an airport runway, not bad for a mammal weighing less than 2 ounces.
All of which means that story number 4 about Ben Stein supporting science other than evolution is TOTALL....... Y BOGUS. Because apparently Ben Stein hates all science, not just evolution. He appeared on the Trinity Broadcasting Network recently and said "the last time any of my relatives saw scientists telling them what to do they were telling them to go to the showers to get gassed." He also said, "That's where science leads you." Not to worry though Ben, despite your worldview, your physician has taken an oath and will therefore still prescribe you life-saving antibiotics created by scientists and you can probably continue to use those eyedrops, you hawk. I certainly hope some scientists were involved in making sure those things were effective and safe.
Well that's it for this edition of the weekly SciAm podcast. You can write to us at podcast@SciAm.com, and don't forget to sign up for the daily digest at www.SciAm.com/daily. For Science Talk, the weekly podcast of Scientific American, I'm Steve Mirsky. Thanks for clicking on us.
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