From a book on Asimov’s life

 A quote from the book by Davidson “A key theme of Lynn Margulis's career would be "symbiosis"—the cooperation of life forms for mutual benefit. This insight would spur her to revive an old idea that modern cells are assemblages of formerly inde- pendent cells. For example, the little mitochondrion that energizes your bodily cells was once an independent cell itself, but it discovered a life of greater safety and leisure within bigger cells than in the liquid jungle outside them. Likewise, the bigger cell benefited from its acquisition of mitochondria, which greatly enhanced its energy reserves. You scratch my back, I'll scratch yours: this is an emerging theme of evolutionary theory, a far cry from the "nature red in tooth and claw" mythology that haunted the Victorian imagination. Sagan and Margulis's relationship was symbiotic, too. He introduced her to biology, explained its basic genetic concepts to her, and had biological contacts (via his relationship with Muller) that might have eased her entry into a biology program in the University of Wisconsin graduate school.”

Another:

One of Lynn Margulis's relatives, the witty Nobel Prize-winning physicist Sheldon Glashow, observed after Sagan became a TV celebrity that Sagan's youthful persuasiveness had "convinced [Lynn] to study biology rather than English." Slyly, Glashow added: "Lynn is possibly,Indeed, in strictly scientific terms, she would become more distinguished than he. She would win admittance to the National Academy of Sciences, which, having a num- ber of members who shared Glashow's attitude but less of his subtlety, would somewhat awkwardly reject Sagan's candidacy.