male sex hormone of testosterone and was the first to successfully synthesize it from cholesterol in 1935. Engineering Germany has been the home of many famous inventors and engineers, such as Johannes Gutenberg, who is credited with the invention of movable type printing in Europe; Hans Geiger, the creator of the Geiger counter; and Konrad Zuse, who built the first electronic computer. German inventors, engineers and industrialists such as Zeppelin, Siemens, Daimler, Diesel, Otto, Wankel, Von Braun and Benz helped shape modern automotive and air transportation technology including the beginnings of space travel. The engineer Otto Lilienthal laid some of the fundamentals for the science of aviation. The physicist and optician Ernst Abbe (1840–1905) founded in the 19th century together with the entrepreneurs Carl Zeiss (1840–1905) and Otto Schott (1851–1935) the basics of modern Optical engineering and developed many optical instruments like microscopes and telescopes. Since 1899 he was the sole owner of the Carl Zeiss AG and played a decisive role of setting up the enterprise Jenaer Glaswerk Schott & Gen (today Schott AG). These enterprises are very successful worldwide up to our time (21st century). In the Thirties of the 20th century the electrical engineers Ernst Ruska and Max Knoll developed at the "Technische Hochschule zu Berlin" the first electron microscope. Biological and earth sciences Emil Behring, Ferdinand Cohn, Paul Ehrlich, Robert Koch, Friedrich Loeffler and Rudolph Virchow, six key figures in microbiology, were from Germany. Alexander von Humboldt's (1769–1859) work as a natural scientist and explorer was foundational to biogeography, he was one of the outstanding scientists of his time and a shining example for Charles Darwin. Wladimir Köppen (1846–1940) was an eclectic Russian-born botanist and climatologist who synthesized global relationships between climate, vegetation and soil types into a classification system that is used, with some modifications, to this day. The Frankfurt surgeon, botanist, microbiologist, and mycologist Anton de Bary (18311888) laid one of the fundamentals of the plant pathology and was one of the discoverer of the symbiosis of organisms. Ernst Haeckel (1834 – 1919) discovered, described and named thousands of new species, mapped a tree of life relating all life forms and coined many terms in biology, for example ecology and phylum. His published artwork of different lifeforms includes over 100 detailed, multi-colour illustrations of animals and sea creatures, collected in his Kunstformen der Natur ("Art Forms of Nature"), an international bestseller and a book