Grassé presents his arguments against neo-Darwinism in his work "L'évolution du vivant" (1973), translated into English as "Evolution of Living Organisms" in 1977. Against the idea which states that the evolution of living things is the product of their adapting to changes in their environments, he opposes living fossils, meaning species which stopped evolving at some point in time and have remained relatively identical to this day regardless of great climatic or geological changes (he cites numerous examples in "Les formes panchroniques et les arrêts de l'évolution", p. 133). Therefore, evolution is in his opinion a process which is not "necessary", it does not occur in living beings under the constraints of external physical forces (cf. "Necessity-utility is not the primus movens of biological evolution", p. 302). To explain evolution he instead thinks that you must look at the internal dynamics of living things.