Lynn Margulis is best known for postulating in 1966 the theory of endosymbiosis, the theory that eukaryotic cells (having nuclear DNA and nucleically differentiated organelles) resulted from the symbiotic fusion of smaller and more primitive prokaryotic cells. Both mitochondria and chloroplasts, critical metabolic organelles in animal and plant eukaryotic cells, for example, are thought to be descended from independent prokaryotic lineages. While her hypothesis was roundly rejected the over the first 15 or so submissions, the theory of endosymbiosis is now one of the most important ideas advanced in evolutionary biology in the last century. As Richard Dawkins put it:
I greatly admire Lynn Margulis’s sheer courage and stamina in sticking by the endosymbiosis theory, and carrying it through from being an unorthodoxy to an orthodoxy. I’m referring to the theory that the eukaryotic cell is a symbiotic union of primitive prokaryotic cells. This is one of the great achievements of twentieth-century evolutionary biology, and I greatly admire her for it.
While I cannot do justice to the topic, several things do stand out to even a blockhead like me.