Johann Karl Nestler, Czech: Jan Karel Nestler (16 December 1783 – 9 July 1842) was an Austrian-Czech scientist in the field of hereditary traits, professor of natural history and agriculture at the Philosophical Faculty of University of Olomouc, dean of the faculty and rector of the university, and doyen of the Czech agriculture science.

Nestler also tried to explain how nature produces new species of animals and plants through forces beyond the hand of man and how breeders control the reproductive process and use modifications, such as inbreeding or outcrossing, for increased production.

[4] Through the examination of the registers of the best stock animals and their offspring Nestler hoped to explain the German: Vererbungsgeschichte (genetic history).

Examination of the records of the ancestors of the best breeding animals, called by Nestler developmental history (German: Entwicklunggeschichte) was for him the reverse side of the same coin.

zur Beförderung des Ackerbaues, Natur- und Landeskde., in which he, among other things, organized the 4th International Congress of Farmers and Foresters (1st time in the lands under control of Austrian Habsburgs) in Brno in 1840.