Herbert Spencer classified himself as a positivist, interested in the discovery of invariant laws of the social world. He differs form Comte by not accepting his version of positivism, especially Comte's sense of positivist religion. While Comte was concerned with the ideas of evolution, Spencer focused on structural evolution. Spencer believed that moral ideas emerged from individual actions. In arriving at this conclusion Spencer used the survival of the fittest perspective. According to Spencer evolution is carried out in three steps: (1) an increase in integration, (2) an increase in differentiation and (3) a movement from confusion to order. This is very important to the legitimation of sociology as a science. He also stressed that sociology is linked to, and should draw upon other sciences such as biology and psychology. Another important insight by Spencer was his way of seeing societies as organic bodies. Both entities increase in size and are subject to structural and functional differentiation. An increasing division of labor also characterizes them both. Spencer described societies as simple, compound, doubly compound, or trebly compound, in order from simplest to most complex.

Spencer-Principles of Sociology
This site is by one of RU's own. It gives a good description of Spencer's life and has part of the text from The Principles of Sociology.

The Origin of Species-Charles Darwin
This gives the text of the famous work by Charles Darwin titled The Origin of Species. This site provides the text of the book, which will help in studying Spencer's descriptions of evolution in society.

Reasons for Dissenting from the Philosophy of M. Comte
This is the text of one of Spencer's many works. He wrote this to discern his work from the work of Auguste Comte, who's work was quite similar.