Wilhelm Bölsche (1861-1939) is the author of a poetic history of the evolution of love entitled Das Liebesleben in der Natur (1898-1903). This work, inspired by the writings of biologist Ernst Haeckel, was greatly successful in Germany at the beginning of the 20th century. Freud kept a copy of the three volumes in his London library and cites the text in his lectures on an Introduction to psychoanalysis. Bölsche develops an Entwicklungsgeschichte (history of evolution) of the distinguishing sexuality of several types of love (oral, anal and urinary). In addition, he describes the "zoological reactionary" homosexual and ties this sexual behaviour to the history of the development of anal sexuality. This paper will address an excerpt on this topic from Bölsche's text that has been translated for the occasion. The task at hand is to prepare the ground for a study of German evolutionism, both popular and scientific, and its ties to psychoanalysis.