Lynn Margulis was a professor of biology at Boston University. She had provocative ideas about many of the important episodes in the history of life, including the origin of eukaryotes. In several articles and books, Dr. Margulis built a strong case for the theory that eukaryotic cells arose as communities of prokaryotes rather than by gradual modification of individual cells. According to this concept, known as the "endosymbiotic theory," chloroplasts and mitochondria are the descendants of prokaryotes that took up residence within larger bacterial cells.
Dr. Margulis also had an active interest in the diversity of contemporary organisms, and she is coauthor of Five Kingdoms: An Illustrated Guide to the Phyla of Life on Earth. This interview and the following chapters develop an important theme of biology: To understand the diversity of life we must trace its evolutionary history.
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Dr. Margulis, what motivated you to choose a career in biology?
As an undergraduate at the University of Chicago, I took an introductory biology course based on one question: What is inherited from generation to generation? James Watson had taken the same course several years earlier, and I remember the Watson-Crick model being discussed when I was a student. I found that whole problem fascinating, and by the end of the course I knew I wanted to study genetics. It was that simple.
Although you were trained as a geneticist, you have a broad interest in the evolution of biological diversity, which is showcased in your book Five Kingdoms. Nearly all biologists now accept the classification of organisms into Five Kingdoms, as proposed by Robert Whittaker in a paper published in 1969. Considering the problems with the two-kingdom classification's attempt to call everything either a plant or an animal, why did it take biologists so long to adopt a new view of biological diversity?
Historical inertia. Whittaker wrote a version of his broad classification of organisms in 1959, but the concepts in the paper were continually rejected. Whittaker was a perfectionist in every sense of the word. He wouldn't send in a paper until every sentence was perfect. He wouldn't even speak a sentence until every word was perfect. And he said that papers on the Five Kingdoms were the only ones in his whole career that were repeatedly rejected. He finally got it into The American Naturalist, which had the reputation for tolerance.
What happened between '59 and '69 that made biologists more receptive to Whittaker's five-kingdom concept?
Molecular biology ... and cytology ... and electron microscopy. That is, the evidence for his concept became much clearer. Whittaker's classification arguments were ecological. For example, it always disturbed him that the fungi were considered plants because their role as decomposers has nothing whatsoever to do with the primary production of food. As an ecologist studying organisms in the field, Whittaker saw primary producers, consumers, and decomposers: plants, animals, and fungi. But he didn't know the microorganisms well. Whittaker and I spent a couple of days going over groups of microorganisms together, and he welcomed my analysis. He agreed to write the foreword to Five Kingdoms, but by that time he was dying of cancer. All his life he wanted to do a book like that himself, but it just wasn't possible; he didn't have the time and he didn't know the microorganisms.
Let's go back even further in time to the origin of life. What is your evaluation of the prevailing theory that spontaneous chemical evolution on the early Earth produced the forerunners of cells?
The monomers [amino acids and nucleotide base pairs] can be produced in laboratory simulation experiments of the early Earth without life itself. Researchers now have as many as 80 nucleotides spontaneously associating in the absence of enzymes. And when lipids are added to mixtures of organic compounds, they tend to surround and concentrate amino acids, peptides, nucleotides, and nucleotide polymers.
Astronomical cycles-tidal cycles, light cycles, hot and cold-may have been important for these chemical processes to occur early on in Earth history. One of the best techniques for concentrating organic matter is to freeze it. If you freeze it, you take the water out. And what's left are high concentrations of organics. Then you dissolve it and freeze it again. Just adding the water back allows chemistry to go on that couldn't go on otherwise. And taking the water away again concentrates the organics again. And you're not exactly where you were the first time.
We've covered about 4 billion years of Earth history. I'd like to finish with a question about the present. What qualities do you like to see in your students?
Well, certainly intellectual curiosity. One problem I'm observing is that students are scared and they want jobs, or they're here because their parents want them to be, which is very sad. I think science should be taught as a liberal art. I try to resist the pressures to make technicians out of everybody. If they don't get exposure to liberal arts thinking at the college level, they're not likely to get it for the rest of their lives. Students, like scientists, have to stop trusting authority and start looking at nature and people for themselves.
Biota of the Isle of Man
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