Study
On the origin of mitosing cells
Sagan, Lynn
Journal of Theoretical Biology, 1967
Assembles comparative evidence — the presence of their own DNA in mitochondria and chloroplasts, their division independent of the cell, their membranes and their resemblance to bacteria — into an argument that these organelles descend from free-living bacteria taken up by an ancestral cell.
- Studied in
- Eukaryota, Bacteria
- Sample size
- synthesis of comparative cell biology
The features of mitochondria and chloroplasts are consistent with descent from engulfed bacteria rather than with origin from within the host cell.
What it means
The authors' reading, and ours. Where they differ, that difference is the point.
How the authors put it
Key eukaryotic organelles are the descendants of once free-living bacteria retained inside a host cell.
How NatureHQ reads it
The paper that revived an idea proposed decades earlier and largely dismissed, and the one worth reading for how an argument gets built from disparate evidence. No single observation carried it. Own genome, own division, double membranes, antibiotic sensitivity and later sequence comparison each pointed the same way independently, and the case became compelling when they stopped being explainable separately.
- A 1967 synthesis; the decisive genomic evidence came later, and several of its specific proposals have not held up.
- The origin of other eukaryotic features it addressed is not accepted in the form proposed.
What this study is used for on NatureHQ
One study can inform several subjects. Here is everywhere this one is cited.
Endosymbiosis
Mitochondria descend from free-living bacteria taken up by an ancestral cell. They are not bacteria now: most of their genes moved to the host nucleus, and none can live independently.
Endosymbiosis
No single observation established endosymbiosis. Own DNA, own division, double membranes, bacterial-type ribosomes and phylogenetic placement each point the same way for separate reasons.
Published by: Elsevier journalsPublished in an Elsevier journal.
doi.org/10.1016/0022-5193(67)90079-3
Checked against Crossref on 2026-09-28, and they agree on the title, the authors and the year.
NatureHQ summarises research in its own words and does not reproduce published text. Reviewed 2026-09-04.