Yesterday, Dorion Sagan announced on Facebook that his mother, the biologist Lynn Margulis, "died peacefully in her sleep at home surrounded by family." Lynn Margulis is famous for transporting endosymbiosis theory from the outskirts of biology to its core. Because of her, it is now widely accepted that certain organelles in plant and animal cells came from free-living bacteria. For example, mitochondria, the power factories in our own cells, descended from purple bacteria. The first part of Margulis' career was a wild success; the second part was deeply problematic. Many felt that she took the symbiosis idea too far, and her constant attacks on Neo-Darwinism were not rewarded—she believed that mutation did not explain biological novelty and instead located, yes you guessed it, symbiosis as the source of biological innovation. We will not get into her opinions on AIDS. Above all, Margulis was a major intellectual force of the 20th century, she did transform a huge part of her field, and her books overflow with brilliant ideas and insights.

From Symbiotic Planet:

As the material stuff from which all living bodies are made, we have in another sense been around since the origin of the universe. The matter in the bodies of all forms, including, of course, mammals like us, can be traced to the carbon, nitrogen, oxygen, and other elements that were made in the supernova explosions of stars.
Margulis's first husband, Carl Sagan, introduced me to those exploding stars. She introduced me to the world of microscopic life. She and he have come and gone.