Spencer's ideas appeared first in magazine articles and were published in a series of books that he constantly rewrote and revised. His most important ideas (on evolution, especially) appeared in the 1850s and 1860s, and after 1870 or so he had little new to say. | Spencer's ideas appeared first in magazine articles and were published in a series of books that he constantly rewrote and revised. His most important ideas (on evolution, especially) appeared in the 1850s and 1860s, and after 1870 or so he had little new to say. |