Two contrasting mechanisms responsible for the creation of genetic variants are described: one is the manifestation of the limited accuracy of the cellular machinery for DNA replication, the other results from the ability of cells to repair damaged DNA. Replication‐dependent variants and those caused by episodical DNA damage enhance the probability that a small fraction of a cell population may survive a sudden (physical or biological) change of environmental conditions. Replication‐independent variants arise during persistent but not immediately lethal stress (e.g. starvation) of a non‐dividing population. The variants observed under these conditions are of selective advantage because they are able to cope with the particular stress situation. The molecular basis of their creation is a matter of intensive debate.