In the 1960s, Margulis proposed that key cellular organelle…

In the 1960s, Margulis proposed that key cellular organelles, specifically mitochondria and chloroplasts, originated from once free-living bacteria that entered into a symbiotic relationship within a host cell[1][3][5]. She first detailed this theory in her influential 1967 paper “On the Origin of Mitosing Cells,” which was notably rejected by more than a dozen journals before publication[3]. At the time, her ideas were met with widespread skepticism and resistance from the scientific establishment, making her persistence especially remarkable[3].