Tuesday, December 15, 2009
The Tree of Life is commonly associated with Charles Darwin, though its iconography predates the theory of evolution. We speak with a local professor of biology about the perceptions of the Tree of Life before and after Darwin.
MAUREEN CAVANAUGH (Host): I'm Maureen Cavanaugh, and you're listening to These Days on KPBS. It’s one thing to talk about the interconnectedness of life on earth; it’s another to try to visualize it. How does one map the history of a group of living things in a way that’s both legible and visually pleasing? One image that has proved useful for scientists is the tree of life. It’s a very old concept in human history but for the past 200 years or so it’s been used to show the relationships and progression of species. As part of the ongoing celebration of the 200th birthday of Charles Darwin, the San Diego Natural History Museum presents a lecture tonight about the tree of life, and my guest is the presenter, Dr. David Archibald. He’s professor of Biology at San Diego State University. And, Dr. Archibald, welcome to These Days.
DR. DAVID ARCHIBALD (Professor of Biology, San Diego State University): Thank you. Good morning, Maureen.
CAVANAUGH: Good morning. When most people think of the tree of life they associate it with Charles Darwin and evolution. Tell us exactly what are we talking about when we’re talking about the tree of life?
DR. ARCHIBALD: Well, first I think you can say that everybody talks about their family tree and it’s the same analogy. In fact, it goes more than analogy because we’re talking about relationships. And the tree of life, although we – a lot of people associate it with Charles Darwin, it was around well before Darwin, almost 100 years – actually probably was first started being used about the time he was born in 1809. That’s actually technically the first tree of life done by Lamarck in 1809, the same year that Darwin was born.
CAVANAUGH: Right. What – Let’s talk about Charles Darwin for just a little bit longer. What does his tree of life represent? What do you see on that?
DR. ARCHIBALD: His tree of life, in “The Origin of Species,” published November 24th, 1859, just a little over 150 years ago, there’s one figure in it. It’s a foldout and it shows a hypothetical tree of life. He’s trying to tell us about how things originate and evolve and change and become extinct. It doesn’t actually show any real plants or animals on it. It’s completely hypothetical.
CAVANAUGH: I see. And it’s the only illustration in “The Origin of Species,” right?
DR. ARCHIBALD: That’s it, umm-hmm.
CAVANAUGH: Isn’t that interesting. Tell us about some of the other tree of life’s – one trees of life that predate Darwin.
DR. ARCHIBALD: Well, I mentioned the one by Lamarck which was the first one to arguably show the relationships of, in this case, animals. There was one done in 1801 by an obscure French botanist that is kind of interesting. It’s a tree showing trees, the relationship of plants. There’s no mention of evolution in it but it actually is showing relationships of organisms but nothing about evolution in that one. So Lamarck is the first to do that. And then from then on, from about 1840 onwards, we start to see things that are very treelike, showing relationships of plants and animals.
CAVANAUGH: This image of the tree is found – was so accessible for scientists. They really liked it so much. When was the first published tree of life that you’re aware of?
DR. ARCHIBALD: The first one was this one in 1801 but it was very obscure and we know little about it. There’s maybe only one copy of this volume still left that I know of. Lamarck’s in 1809, I don’t know how many were published but it’s well known and it’s replicated all the time on like Wikipedia on the net so you can see it there. And then from then on, a lot of publications of the tree of life. I might point out, one of the most famous trees of life that everybody associates with Charles Darwin was done in his notebook in 1837, 1838, and it was not published. And we only see it now on – in publications but it was actually something he never intended for publication. It’s the one that everybody sees, this little tree with A’s and B’s on it.
CAVANAUGH: Right, right. It’s really just a little scribble.
DR. ARCHIBALD: Absolutely.
CAVANAUGH: Yeah. The one in 1801 that you refer to, the botanist one, is Augustin Augier, is that correct?
DR. ARCHIBALD: That’s right.
CAVANAUGH: And that was rooted, though, in a creationist perspective as opposed to evolution.
DR. ARCHIBALD: Well, we have to be a little careful trying to read exactly what somebody says. I don’t think he said anything about how the tree came about. The idea of what causes the tree to form, Lamarck definitely was evolutionary but then later in the 1830s and ‘40s, there were trees done by Hitchcock, who was the guy who got me into – interested in this.
DR. ARCHIBALD: Hitchcock and Agassi, who’s more famous, and a couple other people, Miller, had trees of life but their mechanism was creation, basically Biblical creation, while others such as Darwin and others afterwards, Haeckel, who was definitely evolution was the mechanism. So we had two different groups, one creationists and one evolutionary, using the same representation or the fancy word, iconography, to show relationships.
CAVANAUGH: That’s fascinating. I’m speaking with Dr. David Archibald, professor of Biology at San Diego State University. We’re talking about the iconography of the tree of life. He’s going to present a lecture on it at the San Diego Natural History Museum later today. Tell us a little bit more about Jean Baptiste Lamarck because his tree of life was prior to Dawin’s and it was an evolutionary tree of life.
DR. ARCHIBALD: Absolutely. The thing about Lamarck and I think it’s specifically people who are not in science often have this view that, oh, somebody was wrong, so they must be a bad scientist. This is a case of Lamarck and other people afterwards, it’s not the case at all. Lamarck was a fantastic scientist, very brilliant man. He just happened to be wrong about the mechanism of evolution. But he and, interestingly, Charles Darwin’s grandfather, Erasmus Darwin, had the same ideas that we now call Lamarckian use and disuse. But Lamarck certainly was right showing us an evolutionary tree, he just was wrong about the mechanism of evolution.
CAVANAUGH: I see. So the idea that the species developed into – they progressed along the line of this tree of life was correct but the mechanism and exactly how they got there was a little messed up.
DR. ARCHIBALD: Right. He thought that – a famous example is giraffes, that they stretch their neck a little bit and then they’re going to pass that on to the next generation. It doesn’t work that way.
CAVANAUGH: I see.
DR. ARCHIBALD: It goes through the genes, as we know.
CAVANAUGH: Now I wonder, how did – the scientists must’ve latched onto this idea in part at least because it was such an accessible thing for nonscientists to see. I wonder, how did the public perceive these various trees of life?
DR. ARCHIBALD: That’s a little harder to judge. I don’t presume to be an expert on that. I have the feeling that the one thing is that at the time of Darwin, people didn’t like the idea of that oh, we’re descended from apes and, of course, we know we’re not descended from apes; they’re our nearest relatives. So I think there may have been somewhat of a negative view. In the same token, I think people like to see, oh, this is where we’re supposed to fit on the tree. So I think there must’ve been both a like and a dislike over his representations.
CAVANAUGH: Tell us a little bit more about how you got interested in researching all these various trees of life.
DR. ARCHIBALD: Well, I’m a paleobiologist, an evolutionary biologist, and I draw trees all the time in a practice called cladistics that we’ve now got wonderful computer mechanisms for doing this. And I happened to buy a book down at, unfortunately, the now defunct Wahrenbrock’s here in San Diego, and behind the counter were a series of leather bound books which they had out there for people who wanted to buy book by the feet so they could put on their shelf to look pretty, and this one happened to catch my eye because I knew of this guy Hitchcock. And so I opened up this book and there’s a figure in it, a foldout of a tree of life that I referred to earlier. And I looked at the date and it’s 1852, and the first edition of this book is 1840, that’s 19 years before Charles Darwin. And so at first I thought, well, is Hitchcock trying to tell us about evolution before Darwin by almost 20 years? Turned out, no. It’s his creationist view of how things related in a tree of life so he was definitely a creationist all his life, a scientific creationist, I must say.
CAVANAUGH: Now, Edward Hitchcock, he was a geologist, right?
DR. ARCHIBALD: He was a geologist but also what we would call a paleontologist today. His fame was finding and describing footprints in the Connecticut River Valley that turned out to be dinosaurs. He thought they were giant birds and he never accepted the idea of dinosaurs in his lifetime.
CAVANAUGH: The thing that strikes me when you talk about the various trees of life, the ones that predated Darwin and the ones that were in the – still in the 19th century after Darwin, is really some of them are quite beautiful.
DR. ARCHIBALD: Yes, absolutely. The person – Well, the one by Hitchcock is a hand-colored drawing and I think some people have, from the article I did about this and put it online—you can find it there—and it’s a hand-colored diagram. And Ernst Haeckel also did, to me, rather gothically looking diagrams. He was the one that really popularized the idea of trees of life or what he called phylogenies.
CAVANAUGH: And what’s the difference?
DR. ARCHIBALD: There’s really no difference. The – Well, actually, the trees of life the way I’m talking about it, you could have a creationist tree of life or you could have an evolutionary tree of life. Haeckel was the one who coined the term phylogeny, which simply means the history of a group. And so when we say the word phylogeny, we really mean an evolutionary tree of life.
CAVANAUGH: Now, as science has progressed, as our understanding of evolution has become deeper, scientists still use this iconography of the tree of life but it’s much pared down and it’s much more complex. Does that tree of life still work as an image for how we’re interconnected through evolution?
DR. ARCHIBALD: It works fine for what we, quote, call higher life, actually a rather poor term, a more complicated life such as ourselves, the vertebrates and higher plants and so forth. But a lot of things, bacteria and so forth, have what’s called horizontal gene transfer and so it becomes rather a tangled web and sometimes people talk about the web of life. So the iconography, you’ve got to be careful. We’re a visual species and so when we have a tree, we have this view of how life occurred and now we realize that many of the species on this planet may have – be related to each other in a web form. It doesn’t mean you can’t talk about a tree of life, it just means we have to realize that the relationships, the history of life on this planet is more complicated than a simple tree.
CAVANAUGH: And you will be lecturing this evening as part of the Natural History Museum’s exhibit celebrating the life of Charles Darwin, as I said earlier. Tell us a little bit about what that exhibit is like. What’s on display there? What will be on display?
DR. ARCHIBALD: It’s a wonderful exhibit. I saw it when it was first in the American Museum of Natural History in 2006, and they’ve done just a wonderful job putting up – It goes over the history of Darwin’s life and the reconstruction of his study, his time on the Galapagos Islands, his early life, and today how we think about evolution.
CAVANAUGH: And what will people be able to see from the trees of life? Are you going to be bringing any of the illustrations with you tonight?
DR. ARCHIBALD: Yes, they have a wonderful big theater there and I’ll be showing the trees we’ve been talking about. I’ll have them.
CAVANAUGH: Terrific. Well, thank you so much for talking with us today.
DR. ARCHIBALD: You’re very welcome.
CAVANAUGH: I’ve been speaking with Dr. David Archibald. He’s professor of Biology at San Diego State University. As I say, he will hold a lecture tonight at 6:30 on “The Tree of Life: Perceptions of the History of Life Before and After Darwin,” located at the San Diego Natural History Museum in Balboa Park. I want to let everyone know, for this segment, as all our segments, you can comment online at KPBS.org/TheseDays. Stay with us because coming up, picks for the best music releases in 2009. That’s as These Days continues right here on KPBS.