The "fin-de-siècle" outlook was influenced by various intellectual developments, including Darwinian biology; Wagnerian aesthetics; Arthur de Gobineau's racialism; Gustave Le Bon's psychology; and the philosophies of Friedrich Nietzsche, Fyodor Dostoyevsky and Henri Bergson. Social Darwinism, which gained widespread acceptance, made no distinction between physical and social life and viewed the human condition as being an unceasing struggle to achieve the survival of the fittest. Social Darwinism challenged positivism's claim of deliberate and rational choice as the determining behaviour of humans, with social Darwinism focusing on heredity, race and environment. Social Darwinism's emphasis on biogroup identity and the role of organic relations within societies fostered legitimacy and appeal for nationalism. New theories of social and political psychology also rejected the notion of human behaviour being governed by rational choice, and instead claimed that emotion was more influential in political issues than reason. Nietzsche's argument that "God is dead" coincided with his attack on the "herd mentality" of Christianity, democracy and modern collectivism; his concept of the "übermensch"; and his advocacy of the will to power as a primordial instinct were major influences upon many of the "fin-de-siècle" generation. Bergson's claim of the existence of an ""élan vital"" or vital instinct centred upon free choice and rejected the processes of materialism and determinism, thus challenged Marxism.