Fritz A Lenz (9 March 1887 in Pflugrade, Pomerania – 6 July 1976 in Göttingen, Lower Saxony) was a German geneticist, member of the Nazi Party, and influential specialist in eugenics in Nazi Germany.
The pupil of Alfred Ploetz, Lenz took over the publication of the magazine "Archives for Racial and Social Biology" from 1913 to 1933 and received in 1923 the first chair in eugenics in Munich. In 1933 he came to Berlin where he established the first specific department devoted to eugenics, at the Kaiser Wilhelm Institute of Anthropology, Human Heredity, and Eugenics.
Lenz specialised in the field of the transmission of hereditary human diseases and "racial health". The results of his research were published in 1921 and 1932 in collaboration with Erwin Baur and Eugen Fischer in two volumes that were later combined under the title Human Heredity Theory and Racial Hygiene (1936).
This work and his theory of "race as a value principle" placed Lenz and his two colleagues in the position of Germany's leading racial theorists. Their ideas provided scientific justification for Nazi ideology, in particular its emphasis on the superiority of the "Nordic race" and the desirability of eliminating allegedly inferior strains of humanity - or "life unworthy of life" (Lebensunwertes Leben). Lenz was a member of the "Committee of Experts for Population and Racial Policy". He joined the Nazi party in 1937 while serving as the head of the Kaiser Wilhelm Institute for Anthropology.