The distinctive feature of YanFu’s theory of population was his pioneering analysis of China’s population problems through the application of Darwin’s theory of the survival of the fittest to the survival of races. Yan believed that the deciding factor in the cycle of social stability and unrest was fluctuation in population. He also proposed“two complimentary theories of reproduction”:the“theory of cdueation reducing births”and the“theory of interraeia lmarriage improving off spring.”Yan maintained that human beings must exercise self-control over reproduction，and he advocated eugenics to raise the quality of the population and reduce its rate of inerease. YanFu’s theories，although inappropriate in some ways，were on the whole rational，and they provide some useful guidance for contemporary family planning.