More Science Talk
Steve: Welcome to the Scientific American podcast Science Talk posted on June 29th, 2012. I am Steve Mirsky. On this episode:
Chamovitz: We touch all plants, they respond. If you touch certain plants, we see them respond. And the easiest way of seeing that is the Venus flytrap--we can see the movement. But anytime we touch any plant, there is a cellular and organismic response.
Steve: That's Daniel Chamovitz. He is Director of the Manna Centre for Plant Biosciences at Tel Aviv University. And he is author of the new book, What a Plant Knows. He was in New York City recently and dropped by the Scientific American offices.
Steve: Daniel Chamovitz--great to see you.
Chamovitz: Thanks for having me.
Steve: Sure, thanks for coming in. What a Plant Knows is the name of the book. Let's start there--what does a plant know?
Chamovitz: A plant knows quite a bit. A plant knows what color of light it's seeing--it knows because it can see it; it knows when you're standing on it, because it can feel it; it knows if its neighbor is sick because it could smell it. It knows quite a bit much more than we give them credit for.
Steve: Now, let's talk about the word "knows".
Chamovitz: Yeah, it's controversial.
Steve: Of course, but it's a very clear way of getting across to the reader that the plant has ways to appreciate--even the word "appreciate"--I mean, it's a linguistic, semantic minefield here. But what do we actually mean by "knows."”
Chamovitz: What I say "know", I am talking about "aware and being able to respond.” If you are aware that there is a red light on, you know that there is a red light on; you're aware of it. And then you're responding in a certain way. When you are crossing across the street in the middle of the night and you see a light coming towards you, when you see the light you're aware of the light, and you respond and you run away. When a plant sees a red light, it responds in a certain way. So I say, "It knows that the light is red, because if it would see a blue light or a green light it would respond differently."
Steve: And we're not saying the plant, maybe this is a way to get to it--the plant doesn't know that it knows.
Chamovitz: Now we're on a minefield here of philosophy. I don't think--now I'm saying think--that a plant is self-aware. Now one of my children, when he was 14, would claim that we only think we're self-aware, but we're not really either. We don't want to get into that question.
Steve: We'll bring in some philosophers to discuss this.
Chamovitz: Yeah, I am not claiming that a plant is-self cognizant.
Chamovitz: But on a very basic level, it knows what's going on, it knows what its environment was, and if it didn't it wouldn't survive.
Steve: And one of the really fascinating things about the book is that you discuss these conserved genetic programs; we have the same genes to do a lot of the same things. I mean, even the photoreceptor business--we have the same genes as plants have in some cases.
Chamovitz: Let's take this at two levels. One: Definitely, genetically at the level of the genes that are needed for a cell to function, plant cells and human cells are remarkably similar. You know, for example, one of the big surprises, when they sequenced the plant genome in the year 2000 for Arabidopsis, they found genes for breast cancer. You know, last time I looked at a plant, there weren't many of those breasts, you know. They found genes for mental retardation, they found genes for deafness. But it's sort of a misnomer calling it a gene for breast cancer or gene for deafness because we define these genes by what happens when there's a mutation in them. Gene didn't evolve to cause disease; when they're mis-expressed, then we get the disease. These are all genes that are necessary for the cell to function in a certain way, for example, for cell division. And since we all evolved from single cellular organisms, the same genes that would be necessary for cell division that were present before photosynthetic and non-photosynthetic eukaryotes diverged would also be found between humans and plants. It's, sort of, silly that we didn't even think that that would be the case.
Steve: Right. When you look at it from an evolutionary point of view, you would assume that that would be the case.
Chamovitz: Exactly, but because when we look at plants, we can't identify with them--they're so different. So, we assume that genetically, they're majorly different. Now, there are certain things, of course, that don't exist in animals and in plants that aren't conserved--genes for photosynthesis; genes for flower development; genes you need to make a leaf; just like you don't have genes that you need to make a neuron. But, for example, a gene that's needed to make a hair-like filament coming out of a cell, which make the hairs in our ears--what we call hairs; they're not really hairs.
You know, they're cellular projections. It's a myosin gene; a similar myosin gene in plant is involved in making the little hair-like structures that come out of roots.
Steve: Right, because that's a successful program that many different organisms need to make these kinds of structure, and so the gene which originated, what 2 billion years ago, maybe...
Chamovitz: You know, it's divergent at the nucleotide sequence, but in terms, we could still recognize that they're the same gene. And that's how I actually got to this question of conservation because I really was not interested in studying anything that could smell like medicine. And so when I was a postdoc at Yale University in the mid, early 1990s, I was studying what's called photomorphogenesis--how a plant changes its structure in response to light and dark signals. Nothing you could think up could be more plant-specific than a plant opening its leaves in the light. You know, we like to go to Florida and get a tan, but we don't really, you know, grow a new set of hands. When I cloned these first genes that were involved in photomorphogenesis, they were really unique in all of biology, which fit well to our hypothesis that this was a plant-specific process. But the kicker came one day when I was sort of bored, at the end of my postdoc, and I was just playing on the computer; and just then the early draft of the human genome, the cDNA sequences, were coming out. No on knew what these sequences were; I was just playing on the computer and put my genes in, and these plant-specific genes for photomorphogenesis were in the human genome.
Steve: And do we know what they were doing in the human genome?
Chamovitz: Then we didn't have any idea. It was a real kicker, because I didn't want to touch the human genome, I was just, sort of, playing. Now we know that these same proteins have the same biological function in cells between humans and plants. In plants, when there's a mutation in it, there's an effect in photomorphogenesis. In animals, when there's a defect in it, there's an effect, one of the outcomes in cancer.
Steve: Because all these things have to do with basic, basic processes like growth, and like you said before, cell division or the way cells talk to each other.
Chamovitz: Well, this particular protein is involved in what was called the ubiquitin proteasome pathway, how proteins are degraded. In plants, the main process is photomorphogenesis. In animals, maybe the main process is cell division.
Steve: Let's talk really quickly about the different sections of the book. You basically divide it up into our senses, the senses that we're familiar with--sight, smell, hearing, touch. So real quickly: What does a plant see?
Chamovitz: A plant sees what we see; a plant sees light. But plants don't see pictures. But on a certain level, plants might think that we're visually limited because plants see things that we can't see.
Steve: They see outside of our spectrum.
Chamovitz: They see UV light, and they see far red light and, you know, we can't see that at all.
Steve: Or to make some people happy, they have receptors that get activated by those wavelengths of light.
Chamovitz: I want to continue using the word “see.”
Chamovitz: And can I go on on that one second?
Steve: Sure, sure.
Chamovitz: So if you take someone who's completely blind, and by surgery, in some way giving them a camera, allow them to see just shadows, would we say that that person now has rudimentary sight? He doesn't see pictures, but for that person, being able to differentiate shadows is definitely sight. We would let them be able to differentiate between red and blue, that would be even slightly more sight; that's what plants do. They don't see pictures, but they see colors, they see directions, they see intensities. So I think we can say that plants see.
Steve: And smell?
Chamovitz: Smell yeah. Well, plants smell because we smell them.
Steve: How do you keep a fish from smelling? You cut off its nose.
Steve: But the other meaning--they can?
Chamovitz: They can, now if you want to become very scientific, they can detect volatile chemicals that are wafting through the air. You know, what is smelling? You know, that's some type of chemical in the air--ammonia, Chanel No.5, garlic. You know, it goes through the air, and our receptors in the nose, we smell it, and you get some type of response. Some of it we're cognizant of and some of them we're not. You know, when we start salivating, we haven't chosen to salivate when we smell a barbecue, it just happens. Same thing with the plant; it has well, we assume there are more, so far they have only found one receptor, but we know that plants do respond to more than one type of chemical. And when they get these chemicals through the air, they respond. One of the ways that they're responding is to their neighbor being sick. And so for example, if a neighboring leaf is eaten by an insect or bacteria, the plants would release a chemical in the air, the neighboring plants will absorb that chemical and immediately start making other chemicals that will kill the bugs, for example, it makes them resistant.
Steve: And you talk in the book about experiments to try to determine whether that's actually a communication device from one individual plant to another, and the outcome of those experiments leads researchers to believe it's really something else.
Chamovitz: That's probably a combination of two. On one hand, it probably evolved for communication between branches. There's no direct connection of tissues from one branch to the other. For them to be connected there's a lot of pipes you have to go through. But if one branch can warn its neighboring branch through a volatile signal, it's a much quicker thing. So, then you have a neighboring tree that's, sort of, listening in. Its eavesdropping on its plant, and it also benefits from this conversation. Now you can make all types of evolutionary models--is there an advantage for your neighbors to also know this so that he protects you? Evolutionists or ecologists are split on whether there's an advantage or disadvantage to this.
Steve: We need Bill Hamilton and a lot of intricate mathematics.
Chamovitz: Mathematicians love this type of work. And it also depends, you know, for example, if it's an aspen growth, that's actually all one plant.
Steve: Clearly plants feel something. I mean, if you touch certain plants they immediately respond.
Chamovitz: Well, first off, you touch all plants, they respond. If you touch certain plants, we see them respond. And the easiest way of seeing that it is the Venus flytrap, because we can see the movement; you know, less than one tenth of a second, then it closes. But anytime you touch any plant, there is a cellular and organismic response, and that's because when are plants touched? They're touched in the wind, for example. So, if you see a tree that's on the top of the mountain, and the same tree in a valley, the one on the top will be short and stunted, and the one in the valley will be long with beautiful foliage. If it's being shaken by the wind, it needs to put its energy into making a solid trunk. And that's what touch does--it helps it let know what its environment is.
Steve: You talk about the flytrap to a large extent in the book, and for calcium channel fans out there, you're really going to enjoy the explanations of what goes on. It's all chemical, electrochemical signaling.
Chamovitz: What's funny about this--yes, it is all electrochemical signaling--what's funny about that, is that we've known that for over a hundred years. One of the first people to study the electricity in that was actually the same person who studied potentials in frog nerves; a British scientist, I just drew a blank on his name. But somehow or another, like what often happens in plant biology--and I'm a little paranoid here--is that then the animal biologists just take it over and forget that the plants knew about this originally. It's really scary, you know--it's not scary, it's amazing--that there are no nerves, there are no neurons in plants, but you don't necessarily see neurons for communication. Neurons are one evolutionary adaptation to allow communication.
Steve: Right, we think of it as the one because it's the one we have, so it's our default for that, but we're another variation on a theme.
Chamovitz: Exactly. So, when you touch the hairs on a Venus flytrap, you're getting ion channels activated, which is causing a depolarization, and when the depolarization goes over certain threshold, then it closes, and you get the electric signal propagating throughout the entire leaves. So that's how it closes, that's very "neural", and I'm doing that in quotation marks.
Steve: Air quotes here.
Chamovitz: Yeah, air quotes. There are, I have to emphasize, there are no neurons, but the same basic mechanism is very similar.
Steve: Lets jump a couple of chapters, since we're talking about the flytrap, you have a chapter on plants and what they can remember, and the flytrap also was a great example of the kinds of memory and, it's all chemical functioning that plants can exhibit.
Chamovitz: Well, if we define memory as having some information, storing it and recalling; you know, plants don't remember being in the seed pod, you know, they don't yearn for this, you know, for last year's sunshine; but that's you know, we don't need to anthropomorphize when we say "memory." So, if we take the Venus flytrap, in order for it to close, a bug or a little animal has to touch two hairs; so one hair needs to be touched, it needs to remember that that hair was touched. Once the second one is touched, it'll close, but only if it's within about half a minute.
Steve: And that's the way that the trap knows it's the right size or something it wants.
Chamovitz: Right, because there's again a game. It "wants"--again air quotes--it doesn't want to close, which takes a lot of energy, if it's not going to get a lot of food, so it wants it to be a big bug; "wants" again in air quotes. I'm using these words because it challenges us to think, you know, about ourselves. So you get, really, some type of short-term memory. You touch one hair, wait 20 seconds, touch the other hair; it'll close, wait a minute, it won't close--it has forgotten that the first hair was touched. And the mechanism is all electricity. The potential has gone below the threshold.
Steve: Right. There's a buildup of ions in this channel that then dissipates, and once it gets below a certain level, the memory is lost.
Chamovitz: The memory is lost, which is similar to some of our memory, the way some of our memory mechanisms; there's many memory mechanisms in animals also, some electric, some genetic, some a mixture of both.
Steve: Interestingly, the chapter on hearing, sort of, comes out differently than all the other chapters.
Chamovitz: And because everyone assumes that plants hear.
Steve: And a lot of that comes from the '70s, when people were singing to their plants and playing Mozart for the plants.
Chamovitz: And using, you know, Indian music to their plants. I don't want to say that plants don't hear, but there is no hard evidence. If you look in PubMed database, look what has been published--and that's the only thing we can go on--there's no evidence that plants really respond to music. Now I want to differentiate here between music and hearing. Why would we think that a plant would care whether it's, you know, Meat Loaf, or Led Zeppelin or Bach. You know, when we're talking about plant vision, we don't show them an eye chart and say, "Read the bottom line." When we're talking about plant smelling, we don't say to them, "Differentiate between Chanel No. 5 and Dior." You know, so why would we think music? If we're going to think of plants hearing, we need to think of experiments that might be ecologically relevant, you know; maybe something like subsonic waves through the ground or the very high pitch of an insect. But music--what's the relevance? So, getting back to music, so many people have tried these experiments, and there's all types of new age experiments that say that plants are affected, but the interesting things is that in all those experiments, the plants grew better for the music that the experimenter liked better.
Steve: And to a large extent, these experiments collapse down to a sense that the sensation of the sound wave itself; it's the equivalent of being touched.
Chamovitz: And I will accept that, that auditory is sound waves, and if someone will show that a plant responds to sound waves that'll be great, but so far no one's been able to show that. I would actually predict that we will find that in the future.
Steve: Well, there's one experiment you talk about where there was speaker sound coming at the plant, and then the experimenters put in a fan so that...
Chamovitz: There was no heat coming off the speaker. So most of these experiments have just been done poorly. You know, these are classic experiments that are also done by kids in 6th grade.
Steve: For science projects.
Chamovitz: Yeah, for science projects. And you need to do a good control.
Steve: So when they put the fan in, and it blew the heat away that was coming from the speaker at the plant, the effect blew away.
Chamovitz: You know, one of the researchers into touch, a very good, excellent scientist named Janet Braam--who's now at Rice University, used to be at Stanford--she was one of the people who recognized genetically how plants respond to touch. And one of her experiments in this seminal paper was then to expose her plants--well I guess she likes the Talking Heads--and she exposed her plants to the Talking Heads, seeing if these same genes would go up, and they didn't.
Steve: You talk, one of the great parts of the book--there's a lot of Darwin in the book.
Chamovitz: Darwin is great.
Steve: Darwin was so much smarter than people even realized; but he played his bassoon to plants.
Chamovitz: Darwin played his bassoon. It was one of his experiments, one of his later experiments, but he was also smart enough to say, I think in his own words, that it was "a fool's experiment." And he didn't see any response; he tried to get them to bend towards his bassoon music. His final book was called The Power of Movement in Plants. We still teach that to freshman and undergraduate students. His experiments from 1880 are still being taught and validated. That was an amazing piece of work.
Steve: Yeah, he did such meticulous long-term work with his son on plant growth and discovered many of the basic things that we know about plants.
Chamovitz: And some of it is still being studied. For example, he was showing how a plant responds to gravity, and how plants move. Some of you may have seen or you may have seen time-lapse movies of the plants, sort of, what's called circumnutating--they turn around in circles. But you can only see this with time lapse photography. And Darwin was asking the question, "Is this an endogenous behavior of plants or is it a response to gravity?." Now he didn't have the way of answering those questions, but now his own hypotheses are being checked in the space station.
Steve: Right, that was a fascinating part of the book.
Chamovitz: Isn't that amazing? Yeah.
Steve: As you're reading the book, the thought occurs to you, well, if we could do these experiments in space, it would be really interesting way to figure out whether the plant can appreciate gravity. And then you talk about the fact that they did do these experiments in space.
Chamovitz: Right. And in space, what it ends up is that the movements are minute, but they still remain. Now, that could be because of micro, micro gravity; there's no way of controlling for that yet. There's minute movement, that when you then give a gravitational pull, become large. So, there seems to be an endogenous movement which is then enhanced by gravity.
Steve: You talk about this other experiment, in which the researcher basically, like if, you saw the movie 2001, and you see the guy running on the periphery, on the circumference.
Chamovitz: Around HAL.
Steve: Right, of the rotating wheel because that creates an artificial gravity and so this experimenter created a spinning wheel, spinning really fast, and put the plants in there to see if the acceleration, which would be the equivalent of gravity, would cause them to know up from down.
Chamovitz: And that's exactly what happened. Their movements became exaggerated as soon as they were put in this, sort of, centrifuge. So they had minute movements of one or two or even half a millimeter, which then increased to centimeter circumferences when you put a gravitational pull on it.
Steve: Let's take a minute to talk about Arabidopsis, because it's such a fascinating organism. It's the fruit fly of plants. And most people probably don't know how crucial it's been for botanical research, but genetic research in general also. So tell us about Arabidopsis--what is it and how did it become this lab rat?
Chamovitz: Arabidopsis is a little mustard plant. I think it's called in English thale cress--even if they know it, if you'd ask someone what the thale cress looks like, they wouldn't know. It's quite unremarkable except for a couple of things that botanists about a half a century ago recognized. One that it is small with a very quick generation time; that means it could go from seed to seed in about two months, even six weeks. Two, each plants gives out about 20,000 seeds. And three, it has a small genome, a very small amount of DNA. What this meant for plant scientists is that we could do amazing genetic and genomic experiments in a small amount of time, which means, if you wanted to do your Ph.D. on sequoias, you'd be 90 by the time you graduated, but with an Arabidopsis you could actually start asking amazing questions.
Steve: Ninety? You'd be 900.
Chamovitz: Okay 900, let's say. So, because of work of early botanists who understood this small plant, it was adopted by the molecular genetic community in the 1980s as a model plant. At that time, a lot of people derided it--"What're you going to do with that little mustard?" But now we know, because of the Human Genome Project, and all the work that's gone into Arabidopsis--when I say Human Genome Project, part of the Human Genome Project gave the resources and the money to sequence the Arabidopsis genome; because it was used as a model and from studies on this little plant, which it itself has no economic benefit has led huge, huge advances, both in agriculture and in human medicines. Because you can do experiments much quicker, clone genes, find out what they're doing in this plant, and then adopt it in other organisms. For example, the genes for flowering, what makes a plant flower, were all discovered in Arabidopsis. Some of it was then applied into tree breeding, for example, to cause poplar trees to flower at six months rather than at three years, so you could do breeding.
Steve: So, if you're trying to grow a crop that's resistant to a particular pest, for example, or a disease, a virus, Arabidopsis might be the organism that you try things out in.
Chamovitz: You would definitely try it in Arabidopsis. And until, you know, recently it was the only organism with a genome. Now we have other genomes of other plants; for example, the tomato genome was just published, which is immensely important because there's also diversity in plants. What's good for Arabidopsis isn't good for all plants. Tomato might respond differently. There are pathogens that are specific for tomato, the Solanum species; and there are pathogens that are specific for Arabidopsis, which are the Brassicaceae species in plants. But the basic paradigms that have been outlined in Arabidopsis have held for all plants. And it's also been used to study certain human diseases, like I mentioned earlier with our own research in Arabidopsis.
Steve: So, what is it you said in the book? You have how many MDs in your family--six to seven?
Chamovitz: Six, and two on the way.
Steve: Two are your sons?
Chamovitz: No, not mine. My niece and one of my cousin's children.
Steve: So, this is why you really wanted to not do medicine. You wanted...
Chamovitz: Yeah, my psychologist probably could tell you more about that, but you know, when your father is a doctor and your three uncles are doctors and your sister is a doctor, there's a little bit of familial pressure to go into medicine. And I was really looking to do something that was completely original. And also, when I was 18, I'd been working on a kibbutz, a farm in Israel, and I was really blown away by the idea that you could grow different crops in different ways. I knew nothing about plants, and I was working in alfalfa fields and when you cut alfalfa it grows back and I knew nothing about why. I said, "Wow, if you could put that trait into, like, wheat or corn, you could really solve world hunger." Well, that was a really naïve thing. It's all about where the growing part is--it's above ground, below ground. But that's what got me interested in the idea of how can we feed the world. And with all due to respect to cancer and Alzheimer's, which are hideous diseases that we have to cure, if we don't find a way of getting enough food to everyone in the year 2050, when there will be nine billion people in the world?
You know, we're going to be in major trouble.
Steve: You know, I had the opportunity to meet Norman Borlaug.
Chamovitz: The most important person of the past century.
Steve: Yeah, which, again--most probably never heard of him, but why don't you just briefly tell everybody what he did?
Chamovitz: You know, he really worked, he was wheat breeder, and he did the second Green Revolution in our understanding of how to control wheat growth and how to make the wheat breeding work for the modern times.
Steve: For which he won a Nobel Peace Prize.
Chamovitz: Exactly: not a Nobel Prize in Chemistry, the Nobel Peace Prize. And that's gone unnoticed by the scientific community at large. You know, many of my colleagues, they just don't want to accept the fact that plants are complex organisms or as important as human biology for the future of the world. I'm talking about, you know, professors, big professors in universities around the world. It's not specific for Tel Aviv University. It's also in, you know, NYU or Columbia, you know. Well, plant biology sometimes takes a second seat to human biology, and that's a shame because we might find ourselves in major troubles one day. And we need to encourage our best young minds to be going into these fields, to be solving these problems. Look by, again 2050, we're going to have to grow twice as much food but with less water, less fertilizer, less land--the amount of fertilizers we have, you know, is also limited. So, how are we going to do that? We really need to be able to understand at a very deep level--I would call it at systems level--how plants adopt and respond to their environment, so that we can manipulate this.
Steve: Tell us about your current research.
Chamovitz: So, in my lab we're working on two things. First, these genes that I identified and cloned over 20 years ago, when I was at Yale; yeah, we still don't know how this complex works. This is basic biology. We're trying to understand how a protein complex is built and why this protein complex needs eight sub-units in order to do what it does; maybe we don't even know everything it does. This is work that's being done in Arabidopsis and in Drosophila to do a, we're taking a comparative evolutionary, developmental approach and seeing what we can learn from both of them and then extrapolating one to the other. And in a new project in my lab which, sort of, started just by accident as, sort of, like a side thing, we're trying to figure out why Arabidopsis and other Brassicaceae make a drug that is used in cancer therapy. You know, plants make this thing called glucosinolates, which are a plant chemical which protects them against bugs. And some of these have been used in natural medicine against cancer, and some of them had been used--you know, we know that in cell cycle they stop; in research they can stop cell cycle. So the question I ask in my lab, using an Arabidopsis, is why do plants make these? Is just in case a bug comes? Or does it have a role also in the plant? Now we've found very preliminary results that it could also stop cell cycle in the plants, which is why you want for any other cancer drug.
Steve: You talk in the book about the broccoli; somebody with cancer was advised to use this broccoli extract.
Chamovitz: Right, so the chemical we're talking about comes from broccoli, but broccoli and Arabidopsis are both Brassicaceae; they're very, very, very similar genetically. Now first of all I should say: Do what your doctor says.
Steve: Right absolutely.
Chamovitz: Absolutely, you know.
Chamovitz: The fact that there are, what we call in Hebrew, "grandmother stories" that say, you know, these...
Steve: Buba myses.
Chamovitz: Buba myses--exactly. And some of those, there's truth behind them, but there's not been enough research done on it. A lot of the reason is you can't compound these things; you know, drug companies aren't interested in it. So we're trying to use plants as a model to understand what do these drugs are actually doing; what are these chemicals doing. And again, what we've shown in Arabidopsis is that when they're made, the cells stop dividing, which is exactly what you would want to happen. Now the question is why? What you would want to happen for a drug that would fight cancer.
Steve: Pretty exciting times to be a plant biologist with the genomic information that's available.
Chamovitz: Oh, it's amazing. Yeah it's, you know, I think this new genomic information that's coming out of tomato is going to revolutionize both science, our understanding of developmental biology and of agriculture, because now we'll be able to really do breeding at the level of the gene. It's going to be really a lot of fun going on.
Steve: By the way, Daniel Chamovitz's book, What a Plant Knows, is the first print title published by a new imprint called Scientific American/Farrar, Straus and Giroux, because we and they have teamed up to produce popular science books. Other authors of the new SciAm-FSG books will appear on the podcast in the coming months. We'll be right back after this message from Geoff Marsh at The Nature Podcast:
Geoff Marsh: This week: the Australopithecus diet, five unknowns about bird flu and ambitious plants to save the Baltic Sea.
Steve: Just go to www.Nature.com/podcast.
Steve: That's it for this episode. Get your science news at our Web site: www.ScientificAmerican.com, where you can check out the slide show on the beauty revealed by science. It's called "Empirical Aesthetics." And follow us on Twitter, where you'll get a tweet when every new article hits the Web site. Our Twitter name is @sciam S-C-I-A-M. For Scientific American's Science Talk, I am Steve Mirsky. Thanks for clicking on us.
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