Evolutionary biologist, author and National Medal of Science winner Lynn Margulis (MAR'-guh-liss) has died.
The University of Massachusetts, where she was a professor of geosciences, says Margulis died at her home on Tuesday. She was 73.
Margulis was once married to astronomer Carl Sagan. But she was best known for her theory of symbiogenesis. That theory argues that inherited variation does not come from random mutations in genes but from long-lasting interaction between organisms.
She was also a strong proponent of the hypothesis that the earth acts as a living organism.
Margulis was elected to the National Academy of Sciences in 1983 and received the National Medal of Science in 1999.
She was born in Chicago and enrolled at the University of Chicago when she was 14.