speak of the "Desire for Power" (Machtgelüst); this appeared in The Wanderer and his Shadow (1880) and Daybreak (1881). Machtgelüst, in these works, is the pleasure of the feeling of power and the hunger to overpower. 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. Nietzsche began to expand on the concept of Machtgelüst in The Gay Science (1882), where in a section titled "On the doctrine of the feeling of power", he connects the desire for cruelty with the pleasure in the feeling of power. Elsewhere in The Gay Science he notes that it is only "in intellectual beings that pleasure, displeasure, and will are to be found", excluding the vast majority of organisms from the desire for power. Léon Dumont (1837–77), whose 1875 book Théorie scientifique de la sensibilité, le plaisir et la peine Nietzsche read in 1883, seems to have exerted some influence on this concept. Dumont believed that pleasure is related to increases in force. In The Wanderer and Daybreak, Nietzsche had speculated that pleasures such as cruelty are pleasurable because of exercise of power. But Dumont provided a physiological basis for Nietzsche's speculation. Dumont's theory also would have seemed to confirm Nietzsche's claim that pleasure and pain are reserved for intellectual beings, since, according to Dumont, pain and pleasure require a coming to consciousness and not just a sensing. In 1883 Nietzsche coined the phrase Wille zur Macht in Thus Spoke Zarathustra. The concept, at this point, was no longer limited to only those intellectual beings that can actually experience the feeling of power; it now applied to all life. The phrase Wille zur Macht first appears in part 1, "1001 Goals" (1883), then in part 2, in two sections, "Self-Overcoming" and "Redemption" (later in 1883). "Self-Overcoming" describes it in most detail, saying it is an "unexhausted procreative will of life". There is will to