Geneticist, professor of plant physiology 1905-27, graduate in pharmacology at the Pharmaceutical College 1880, assistant at the Carlsberg Laboratory 1880-87, associate professor, from 1903 full professor, of plant physiology at the Royal Veterinary and Agricultural College 1892-1905, rector of the university 1917-18.
After a successful early career as a physiologist at the Carlsberg Laboratory, Wilhelm Johannsen became increasingly interested in the new science of genetics around 1900. In 1903 he published a paper based on his experiments with pure lines of self-fertilising beans which convinced him that selection for extreme size variations had no effect on the offspring. It was soon considered one of the foundational works of genetics and was translated into German as Über Erblichkeit in Populationen und in reinen Linien. Ein Beitrag zur Beleuchtung schwebender Selektionsfragen (Jena: G. Fischer, 1903). In Johannsen’s view, his experiments with pure lines had important implications for evolutionary theories. In contrast to the importance paid by Darwinians and Lamarckians to the role of small variations in the evolutionary process, Johannsen demonstrated the constancy of the biological type, which led him to formulate his essential distinction between genotype and phenotype in 1909 which was published in Elemente der Exacten Erblichkeitslehre (Jena: Gustav Fischer, 1909). According to Johannsen, environmental factors that influenced the phenotype could not be transmitted to the genotype and the offspring. This contribution to genetics was widely acknowledged abroad and meant a severe blow to Lamarckism. It thus widened the gap between field naturalists, who found it increasingly difficult to legitimise their scientific practises, and laboratory biologists eager to restrict the terrain of exact science to experimental work. After his work on pure lines Johannsen gave up experimental work and focused on discussing current genetic theories and defending exact methods in evolutionary biology. In reviews, textbooks and popular articles he criticised what he regarded as metaphysical approaches and speculative assumptions in biology. His critical epistemology resulted in a controversy in the first decades of the twentieth century with his former teacher, the professor of botany, Eugen Warming, who was offended by the harsh critique that Johannsen put forth against his attempt to integrate evolution and Christianity, his scientific method and his Lamarckian views. Johannsen’s works on evolution include Falske Analogier [False Analogies] (Copenhagen: J.H. Schultz, 1914), Arvelighed i Historisk og Experimentel Belysning [Heredity in the Light of History and Experimentation] (Copenhagen: Gyldendal, 1917) and Biologi: Træk af de Biologiske Videnskabers Udvikling i det Nittende Aarhundrede [Biology: Episodes in the Development of the Biological Sciences in the Nineteenth Century] (Copenhagen: Gyldendal, 1922). From 1924 Johannsen was member of a state commission on degeneration and eugenics. True to his critical epistemology, however, Johannsen remained sceptical of eugenic initiatives. On the basis of his fundamental distinction between genotype and phenotype, he argued that it was impossible to conclude from the appearance of alcoholism, insanity or specific diseases within certain families that these traits were hereditary. Johannsen was thus far from being a genetic determinist, and he argued in several publications that nurture often played a decisive role in the constitution of individuals.
Hans Henrik Hjermitslev