Lynn Margulis and the Question of How Cells Evolved
(excerpts from the book "Doing Biology" by Joel Hagen et al) Modern biology inherited two great theories from the nineteenth century: evolutionary theory and cell theory. Surprisingly, these theories, so central to our understanding of the living world, have had a rather uneasy relationship. Until quite recently, most cell biologists ignored evolution, and most evolutionary biologists ignored cells. The exception to this historical generalization was the chromosomes, which both evolutionary biologists and cell biologists studied. But what about the cytoplasm, the contents of the cell outside the nucleus? Could knowing about other cellular structures (organelles) add anything to …ver más…

Other scientists reported finding DNA in mitochondria. Because these early reports were hotly disputed, searching for DNA outside the nucleus was not the sort of research project that most graduate students would have chosen. Despite warnings, Margulis plunged into the controversial problem for her Ph.D. dissertation. Using radioactively labeled nucleotides, she convincingly demonstrated the presence of DNA in the chloroplasts of Euglena gracilis, one of the curious unicellular organisms that shares both plant and animal characteristics. Margulis wrote her first article on the endosymbiotic theory in 1967, two years after she completed her Ph.D. At the time, she was a single mother without a permanent teaching position. She was also writing her first book on endosymbiosis, which sparked a lively controversy when it was published in 1970. Although it initially brought Margulis notoriety, the controversy over cellular evolution was rather short lived. By the time she published a second book on endosymbiosis in 1981, most biologists accepted important parts of her theory. As a result, Margulis became a scientific celebrity whose success was publicized in both popular and professional magazines.
BACKGROUND TO A CONTROVERSY
In 1970, when Margulis's first book was published, most biologists had never heard of endosymbiosis. Those who knew about it usually dismissed it. In order to succeed, Margulis had to carefully distinguish her