in his essay, 'Progress: Its Law and Cause', published in Chapman's Westminster Review in 1857, and which later formed the basis of the First Principles of a New System of Philosophy (1862). In it he expounded a theory of evolution which combined insights from Samuel Taylor Coleridge's essay 'The Theory of Life' – itself derivative from Friedrich von Schelling's Naturphilosophie – with a generalisation of von Baer's law of embryological development. Spencer posited that all structures in the universe develop from a simple, undifferentiated, homogeneity to a complex, differentiated, heterogeneity, while undergoing increasing integration of the differentiated parts. This evolutionary process could be observed, Spencer believed, throughout the cosmos. It was a universal law, applying to the stars and galaxies and to biological organisms, and to human social organisation and to the human mind. It differed from other scientific laws only in its greater generality, and the laws of the special sciences could be shown to be illustrations of this principle. The principles described by Herbert Spencer received a variety of interpretations. Bertrand Russell stated in a letter to Beatrice Webb in 1923: 'I don't know whether [Spencer] was ever made to realize the implications of the second law of thermodynamics; if so, he may well be upset. The law says that everything tends to uniformity and a dead level, diminishing (not increasing) heterogeneity'. Spencer's attempt to explain the evolution of complexity was radically different from that of Darwin's Origin of Species which was published two years later. Spencer is often, quite erroneously, believed to have merely appropriated and generalised Darwin's work on natural selection. But although after reading Darwin's work he coined the phrase 'survival of the fittest' as his own term for Darwin's concept, and is often misrepresented as a thinker who merely applied the Darwinian theory to society, he only grudgingly incorporated natural selection into his preexisting overall system. The primary mechanism of species transformation that he recognised was Lamarckian use-inheritance which posited that organs are developed or are diminished by use or disuse and that the resulting changes may be transmitted to future generations. Spencer believed that this evolutionary mechanism was also necessary to explain 'higher' evolution, especially the social development of humanity. Moreover, in contrast to Darwin, he held that evolution had a direction and an end-point, the attainment of a final state of equilibrium. He tried to apply the theory of biological evolution to