Answer
On the Origin of Mitosing Cells, Margulis' seminal paper, proposed that eukaryotic cells evolved through the endosymbiosis of bacteria. This theory suggests that mitochondria and chloroplasts originated as independent organisms that were engulfed by a larger cell and gradually integrated into its structure. Margulis' work challenged the prevailing view of cell evolution and laid the foundation for our understanding of the complex origins of eukaryotic life.