 The term "directed mutation" or adaptive mutation is sometimes used with the implication of a process of mutation that senses and responds to conditions directly.When the sense is simply that the mutation system is tuned to enhance the production of helpful mutations under certain conditions, the terminology of "mutation strategies"  or "natural genetic engineering"  has been suggested, but these terms are not widely used.Various mechanisms of mutation in pathogenic microbes, e.g., mechanisms for phase variation and antigenic variation, appear to have evolved so as to enhance lineage survival, and these mechanisms are routinely described as strategies or adaptations in the microbial genetics literature (e.g.,).