Wilhelm Roux published his "The Struggle of Parts in the Organism" ("Der Kampf der Teile im Organismus") in 1881, and Nietzsche first read it that year. The book was a response to Darwinian theory, proposing an alternative mode of evolution. Roux was a disciple of and influenced by Ernst Haeckel, who believed the struggle to survive occurred at the cellular level. The various cells and tissues struggle for finite resources, so that only the strongest survive. Through this mechanism, the body grows stronger and better adapted. Rejecting natural selection, Roux's model assumed a neo-Lamarckian or pangenetic model of inheritance.