1. Margulis, L. Origin of Eukaryotic Cells (Yale Univ. Press, New Haven, CT, 1970).
2. Gray, M. W. & Spencer, D. F. Symp. Soc. Gen. Microbiol. 54, 109–126 (1996).
3. Doolittle, W. F. & Brown, J. R. Proc. Natl Acad. Sci. USA 91, 6721–6728 (1994).
4. Olsen, G. J. & Woese, C. R. Cell 89, 991–994 (1997).
5. Margulis, L. Proc. Natl Acad. Sci. USA 93, 1071–1076 (1996).