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</ref> These theories were initially dismissed (or ignored) by the scientific community. More detailed electron microscopic comparisons between cyanobacteria and chloroplasts (for example, studies by Hans Ris<ref>Ris H, Singh RN (January 1961). "Electron microscope studies on blue-green algae". J Biophys Biochem Cytol 9 (1): 63–80. doi:10.1083/jcb.9.1.63. PMC 2224983. PMID 13741827.</ref>) combined with the discovery that plastids and mitochondria contain their own [[DNA]]<ref>Stocking C and Gifford E (1959). "Incorporation of thymidine into chloroplasts of Spirogyra". Biochem. Biophys. Res. Comm. 1 (3): 159–64. doi:10.1016/0006-291X(59)90010-5.

</ref> These theories were initially dismissed (or ignored) by the scientific community. More detailed electron microscopic comparisons between cyanobacteria and chloroplasts (for example, studies by Hans Ris<ref>Ris H, Singh RN (January 1961). "Electron microscope studies on blue-green algae". J Biophys Biochem Cytol 9 (1): 63–80. doi:10.1083/jcb.9.1.63. PMC 2224983. PMID 13741827.</ref>) combined with the discovery that plastids and mitochondria contain their own [[DNA]]<ref>Stocking C and Gifford E (1959). "Incorporation of thymidine into chloroplasts of Spirogyra". Biochem. Biophys. Res. Comm. 1 (3): 159–64. doi:10.1016/0006-291X(59)90010-5.

</ref> (which had recently been identified as the hereditary material of organisms) led to a resurrection of the idea in the 1960s.  

</ref> (which had recently been identified as the hereditary material of organisms) led to a resurrection of the idea in the 1960s.  

The endosymbiotic hypothesis was advanced and substantiated with [[microbiology|microbiological]] evidence in 1967 by [[American]] biologist Lynn Margulis. A young faculty member at [[Boston University]], Margulis authored a theoretical paper entitled ''The Origin of Mitosing Eukaryotic Cells''<ref>Lynn Sagan (1967). "On the origin of mitosing cells". J Theor Bio. 14 (3): 255–274. doi:10.1016/0022-5193(67)90079-3. PMID 11541392.</ref>. The paper, however, was "rejected by about fifteen scientific journals," Margulis recalled<ref>John Brockman, The Third Culture, New York: Touchstone, 1995, 135.</ref>. It was finally accepted by ''The Journal of Theoretical Biology'' and is considered today a landmark in modern endosymbiotic theory. Drawing heavily from the ideas of Mereschkowski and Wallin, Margulis's endosymbiotic theory formulation is the first to rely on direct microbiological observations as opposed to [[paleontology|paleontological]] or [[zoology|zoological]] observations, which were previously the norm for new works in [[evolutionary biology]].  

The endosymbiotic hypothesis was advanced and substantiated with [[microbiology|microbiological]] evidence in 1967 by [[American]] biologist Lynn Margulis. A young faculty member at [[Boston University]], Margulis authored a theoretical paper entitled ''The Origin of Mitosing Eukaryotic Cells''<ref>Lynn Sagan (1967). "On the origin of mitosing cells". J Theor Bio. 14 (3): 255–274. doi:10.1016/0022-5193(67)90079-3. PMID 11541392.</ref>. The paper, however, was "rejected by about fifteen scientific journals," Margulis recalled<ref>John Brockman, The Third Culture, New York: Touchstone, 1995, 135.</ref>. It was finally accepted by ''The Journal of Theoretical Biology'' and is considered today a landmark in modern endosymbiotic theory. Drawing heavily from the ideas of Mereschkowski and Wallin, Margulis's endosymbiotic theory formulation is the first to rely on direct microbiological observations as opposed to [[paleontology|paleontological]] or [[zoology|zoological]] observations, which were previously the norm for new works in [[evolutionary biology]].