Editing Molecular clock (section)

==Relationship with neutral theory==

The observation of a clock-like rate of molecular change was originally purely [[phenomenology (philosophy)|phenomenological]]. Later, the work of [[Motoo Kimura]]<ref name=Kimura68>{{cite journal | vauthors = Kimura M | title = Evolutionary rate at the molecular level | journal = Nature | volume = 217 | issue = 5129 | pages = 624–626 | date = February 1968 | pmid = 5637732 | doi = 10.1038/217624a0 | s2cid = 4161261 | bibcode = 1968Natur.217..624K }}</ref> developed the [[neutral theory of molecular evolution]], which predicted a molecular clock. Let there be N individuals, and to keep this calculation simple, let the individuals be [[Ploidy|haploid]] (i.e. have one copy of each gene). Let the rate of neutral [[mutation]]s (i.e. mutations with no effect on [[Fitness (biology)|fitness]]) in a new individual be <math>\mu</math>. The probability that this new mutation will become [[Fixation (population genetics)|fixed]] in the population is then 1/N, since each copy of the gene is as good as any other. Every generation, each individual can have new mutations, so there are <math>\mu</math>N new neutral mutations in the population as a whole. That means that each generation, <math>\mu</math> new neutral mutations will become fixed. If most changes seen during [[molecular evolution]] are neutral, then [[Fixation (population genetics)|fixations]] in a population will accumulate at a clock-rate that is equal to the rate of neutral [[mutation]]s in an individual.