Sir

Your leading article “Biology versus physics” questions the existence of Kuhnian paradigms in biology (Nature 391, 107; 1998). I would offer as a candidate the demonstration by Lynn Margulis and others that mitochondria are endosymbionts descended from formerly free-living proteobacteria. For, to those of us interested in both evolution and religion, the confirmation that human and other eukaryotic cells were really bacterial cooperatives (in Whose image?) certainly felt like a double-strength paradigm shift.