Ronald Fisher, full name Ronald Aylmer Fisher (1890-1962), British statistician and geneticist, 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.