The German biologist and artist Ernst Heinrich Philipp August Haeckel (1834–1919) (Fig. 1) was a key figure during the early years of the “First Darwinian revolution”, a time period when the foundation for the development of our modern evolutionary view of the biosphere was laid. Born 16 February 1834 in Potsdam, Haeckel studied medicine at the Universities of Berlin, Würzburg, and Vienna, after graduation from the Domgymnasium Merseburg. When Haeckel was 23 years old (1857), he earned his “Dr. med.” and started to work as a physician. However, after contact with suffering patients, he soon gave up practicing medicine.

After 4 years of experimental work on the systematics of the Radiolaria, Haeckel earned his habilitation at the University of Jena (1861) and became a Privatdozent (lecturer). When his first major monograph on the systematics of the Radiolaria was published (Haeckel 1862), he was promoted to extraordinary (a. o.) professor. Three years later, Haeckel earned a doctorate in zoology (Dr. phil.) at the Faculty of Philosophy (13 July 1865). In the same year, a. o. Prof. Dr. med. Dr. phil. Ernst Haeckel was appointed to the Lehrstuhl (chair) of zoology at the University of Jena. Here, he continued to work as a full (o.) professor until his retirement (Emeritierung) on 1 April 1909. Accordingly, Haeckel was 75 years old when he gave up his duties as an academic teacher, after almost 50 years in office at his alma mater. Haeckel published approximately 700 journal and newspaper articles and 18 major books (Haeckel 1862, 1866, 1868, 1872, 1874, 1878, 1879/1881, 1883, 1894/1896, 1899, 1899/1904, 1901, 1902, 1904, 1905, 1907, 1908, 1917). His artwork, comprised of more than 100 illustrations and watercolours, was compiled and published in his Kunstformen der Natur (Haeckel 1899/1904). Ernst Haeckel died on 9 August 1919, at age 85, in his Villa Medusa in Jena (Hossfeld 2010, 2016).