Rensch was born in
Thale and as a young boy, he took an interest in observing the natural world and discovered a talent for drawing and painting. He served in the German army from 1917 to 1920 and began to observe natural phenomena while he was held prisoner in France. He returned to Germany and began his studies on feather structure under
Valentin Haecker (1864–1927) who had himself studied under
August Weismann. Until the 1930s Rensch held anti-Darwinian and Lamarckian views. Rensch also took an interest in the philosophy of science and was fascinated by
Theodor Ziehen (1862–1950). Rensch also studied expressionist painting and in later life examined the biological roots of art. He received his Ph.D. from the
University of Halle in 1922. He joined the zoological museum of the University of Berlin as an assistant in 1925. In 1927 he participated in a zoological expedition to the
Sunda Islands. He studied the geographical distribution of subspecies of
polytypic species and of complexes of closely related species with attention to how local environmental factors, especially climate, influenced their evolution. In 1929 he published the book
Das Prinzip geographischer Rassenkreise und das Problem der Artbildung that discussed the relationship between geography and speciation. His work in this area would influence
Ernst Mayr, who was also an assistant at the museum from 1927 to 1930, and would contribute to the development of the
modern evolutionary synthesis. In 1937 he was forced to leave the museum because he refused to join the Nazi party, and took a position at a zoological garden in
Münster. In 1947 he published a book that would later be translated into English under the title
Evolution above the species level. The book discussed how the evolutionary mechanisms that drove speciation could also explain the differences between higher
taxa. He introduced the concept of
Artenkreis (which Mayr translated as a "superspecies" and defined as "a monophyletic group of closely related and largely or entirely allopatric species”). It was considered a major document in the modern synthesis. That same year he became chairman of the zoology department and director of the zoological institute at the University of Münster. In 1953 he would take part in a zoological expedition to India. Later in his career he would work extensively in the areas of animal behavior (
ethology), learning, and memory. Rensch also wrote on human behaviour and he suggested that the human evolutionary connection with organisms would lead to sympathy. He published an autobiography in 1979 and remained scientifically active until his death in 1990. ==Biological rules==