Sir Ronald Aylmer Fisher was a British mathematician, whose statistical theories made scientific experimentation far more precise. Fisher showed that by partitioning the variations of a body of data, one can accurately assess how they influence one another and the outcome of the experiment. Used first in biology, his statistical designs quickly became influential and were applied in agricultural, medical, and industrial experimentation. Fisher also shed much light on the roles that mutation and natural selection play in genetics, particularly in human populations.

Being a geneticist, he also showed mathematically that the rate of evolution in a Mendelian population can be limited by the genetic variability of that population; the more variability, the faster the possible evolution, the less variability, the slower the evolution. This he called the Fundamental Theorem of Natural Selection and this theorem has been confirmed experimentally.