A champion of microorganisms throughout her career, Lynn Margulis wrote about cells in ways that changed how most scientists view evolution.

Rather than embrace the belief that random mutation led to new branches in the tree of life, Dr. Margulis argued that evolution is rooted in a web of new and ongoing relationships at the microscopic level as cells infect or consume one another. As these cellular relationships prosper, evolution progresses with one encounter building on another.

“At some point an amoeba ate a bacterium but could not digest it,’’ she said, offering an example in an interview Discover magazine published in April. “The bacterium produced oxygen or made vitamins, providing a survival advantage to both itself and the amoeba.’’


Dr. Margulis, a distinguished university professor of geosciences at the University of Massachusetts Amherst who was awarded the National Medal of Science by President Clinton in 1999 for her work in evolution, died Nov. 22 in her Amherst home.

She was 73 and had suffered a stroke a few days earlier. Given the history of strokes in her family, she had left instructions that she did not want to be kept alive through artificial means.

“She leaves us a legacy of academic accomplishment brought about by her original thought and tireless inquiry into multiple fields of science that look at how the world functions and how that magnificent world has developed over time,’’ said Robert C. Holub, chancellor of the university. Dr. Margulis, who was elected to the National Academy of Sciences in 1983, was known for the breadth of her intellect, which extended far beyond the area of her accomplishments.

“Where a lot of other scientists tend to not learn outside their field, my mom wasn’t afraid to look outside her discipline and try to understand what others were doing,’’ said her daughter Jennifer of Ashland, Ore.


Steve Goodwin, dean of the UMass-Amherst College of Natural Sciences, said in a statement that Dr. Margulis “was a different kind of scientist, one who does not come along very often. Her great gift was making connections, connections that others just couldn’t make.’’

That talent sometimes led Dr. Margulis into controversial realms. For example, she supported and worked with scientist James E. Lovelock, whose Gaia theory suggests that the earth, its atmosphere, and its inhabitants collectively form a self-regulating system.

Dr. Margulis also questioned the general medical understanding of AIDS.

“Our claim is that there’s no evidence that HIV is an infectious virus, or even an entity at all,’’ she told Discover magazine for the April interview. “There’s no scientific paper that proves the HIV virus causes AIDS.’’

Dr. Margulis did not shy from challenging orthodox beliefs.

“I don’t consider my ideas controversial,’’ she told Discover. “I consider them right.’’

Born Lynn Petra Alexander, she grew up on Chicago’s South Side and attended the University of Chicago’s Laboratory Schools, entering the university itself at 14. She did so in part to spend less time at home, where as the oldest child she spent much time helping care for younger siblings.

“Her act of teenage rebellion was to get into college,’’ said her son Dorion Sagan of Toronto. “That sheds light on her future trajectory. Her intellectual life was this beautiful act of rebellion. That explains why she wasn’t afraid to not conform.’’


At 16, Dr. Margulis met Carl Sagan, who would become a famous cosmologist and host of the PBS TV series “Cosmos.’’

They married in 1957, the year she graduated from the University of Chicago.

Dr. Margulis graduated from the University of Wisconsin in 1960 with a master’s in genetics and zoology, and from the University of California, Berkeley, with a doctorate in biology.

Her marriage to Sagan ended in divorce in 1963. He died in 1996.

While she was living in the Boston area, she met Thomas Margulis, whom she married in 1967. Their marriage ended in divorce in 1980.

“I quit my job as a wife twice,’’ she told The University of Chicago Magazine in 2004. “It’s not humanly possible to be a good wife, a good mother, and a first-class scientist. No one can do it; something has to go.’’

Dr. Margulis taught at Boston University for 22 years before moving to UMass-Amherst in 1988.

“She was somebody who trod fearlessly into a variety of fields and changed them,’’ her son said. “She created her own authority by her combination of expertise and fearlessness and innovative curiosity.’’

In a scientific world where the praise or disapproval of colleagues can prompt conformity, “she was not dissuaded by peer pressure,’’ her son said. “I think most people are stymied by a need to look good and to find a general approval. That wasn’t part of what made her tick. She was a deep original thinker.’’


In addition to her son and daughter, Dr. Margulis leaves two other sons, Jeremy Sagan of Framingham and Zachary Margulis-Ohnuma; three sisters, Joan Glashow of Brookline, Sharon Kleitman of Newton, and Diane Alexander of Washington, D.C.; a half-sister, Sara Alexander of New York City; three half-brothers, Mark Alexander of Chicago, Robert Alexander of Bethesda, Md., and Michael Alexander; and nine grandchildren.

Dr. Margulis’s family is preparing a celebration of her life and scientific work, which will be announced.

In Amherst, Dr. Margulis lived next door to the home of poet Emily Dickinson. The side-by-side proximity led to a sort of intellectual bonding between the evolutionary scientist and the 19th century poet. “She felt somewhat a kinship with Dickinson and was, herself, a sort of amateur Emily Dickinson scholar,’’ Dorion Sagan said of his mother.

“She loved memorizing Dickinson poems,’’ Dr. Margulis’s daughter Jennifer said. “I think she just spoke to my mom.’’

Bryan Marquard can be reached at bmarquard@globe.com.