This paper investigates the development of the philosophy of biology in analytical philosophy of the early 20(superscript th) century. I'll begin by locating the place of the philosophy of biology in the logical empiricist program. Major philosophical discussions of biology in the earlier literatures related to the program of the unity of science propelled by logical empiricists since the 1920s, for biology was considered the most crucial science. To realize the ambition of uniting the various sciences, the main affair for logical empiricists was to demonstrate that biological science can be reduced to physical science. Teleology in traditionally biological researches became the central target at which the logical empiricists aimed; and reduction was the most powerful arrow in their hands. I shall show how logical empiricists reduced a teleological explanation to a nomological one. Can biological science, however, be successfully reduced to physical science? Emergentism and the problem about the nature of life formed the other large obstacle besides teleology against logical empiricists' program. Thus I also have to consider the arguments used by logical empiricists to overcome emergentism and to advance reductionism. In the final part, I shall make some preliminary observations on the trend of the philosophy of biology after 1970s.