sociology. He proposed that society was the product of change from lower to higher forms, just as in the theory of biological evolution, the lowest forms of life are said to be evolving into higher forms. Spencer claimed that man's mind had evolved in the same way from the simple automatic responses of lower animals to the process of reasoning in the thinking man. Spencer believed in two kinds of knowledge: knowledge gained by the individual and knowledge gained by the race. Intuition, or knowledge learned unconsciously, was the inherited experience of the race. Spencer in his book Principles of Biology (1864), proposed a pangenesis theory that involved "physiological units" assumed to be related to specific body parts and responsible for the transmission of characteristics to offspring. These hypothetical hereditary units were similar to Darwin's gemmules. Sociology Spencer read with excitement the original positivist sociology of Auguste Comte. A philosopher of science, Comte had proposed a theory of sociocultural evolution that society progresses by a general law of three stages. Writing after various developments in biology, however, Spencer rejected what he regarded as the ideological aspects of Comte's positivism, attempting to reformulate social science in terms of his principle of evolution, which he applied to the biological, psychological and sociological aspects of the universe. Given the primacy which Spencer placed on evolution, his sociology might be described as social Darwinism mixed with Lamarckism. However, despite its popularity, this view of Spencer's sociology is mistaken. While his political and ethical writings had themes consistent with social Darwinism, such themes are absent in Spencer's sociological works, which focus on how processes of societal growth and differentiation lead to changing degrees of complexity in social organization The evolutionary progression from simple, undifferentiated homogeneity to complex, differentiated heterogeneity was exemplified, Spencer argued, by the development of society. He developed a theory of two types of society, the militant and the industrial, which corresponded to this evolutionary progression. Militant society, structured around relationships of hierarchy and obedience, was simple and undifferentiated; industrial society, based on voluntary, contractually assumed social obligations, was complex and differentiated. Society, which Spencer conceptualised as a 'social organism' evolved from the simpler state to the more complex according to the universal law of evolution. Moreover, industrial society was the direct descendant of the ideal society developed in Social Statics, although Spencer now equivocated over whether the evolution of society would result