In 1943, published in a paper entitled “Mutations of Bacteria from Virus Sensitivity to Virus Resistance,” microbiologist Salvador Luria, biophysicist Max Delbrück, and bacteriologist and geneticist Alfred Hershey discovered that mutations occur at a constant rate. In 1969, they were awarded the Nobel Prize in Physiology and Medicine “for their discoveries concerning the replication mechanism and genetic structure of virus.”

The Luria-Delbrück Experiment opened the question, are mutations inherent to microbes for the purpose of adaption to rapidly changinging environments and not for evolution? While microbe resistance through mutation is a logical mechanism for evolution, the reality is the bacteria have remained a bacteria and the virus has remained a virus. Preexistent genetic variants determine the range of mutations. Pierre-Paul Grassé, president of the French Academy of Sciences, observed, “bacteria, the study of which has formed a great part of the foundation of genetics and molecular biology … stabilized a billion years ago.”

The question is whether the mutations are the “raw material for evolution” or nature’s means for the microbes to adapt to the environment. In a 2009 review article by entitled “Darwinian evolution in the light of genomics”, published in Nucleic Acid Research, Eugene V Koonin concluded, “There is no consistent tendency of evolution towards increased genomic complexity” through mutation as expected with current evolutionary theories. Mechanisms of evolution remain beyond any known natural law.

Reflecting on the role of mutations, Grassé questioned, “What is the use of their unceasing mutations if they do not change?” Grassé concludes, “the mutations of bacteria and viruses are merely hereditary fluctuations around a median position; a swing to the right, a swing to the left, but no final evolutionary effect.” Microbes undergo constant mutations, but do not evolve – mutation stasis.

*Nucleic Acids Res. 2009 March; 37(4): 1011–1034