In Evolutionary Epistemology, knowledge is compatible with reality, that is, the knowledge which has survived error elimination. In linking the philosophy of science to evolution and in thus making epistemology evolutionary, Popper has also established his philosophical realism on a more secure basis. Evolutionary Epistemology also throws light on another problem which has been troublesome in Popperian thought. In order to explain the growth of knowledge and to show how new theories supersede old theories by explaining new facts as well as old facts explained in the earlier theory, Popper has introduced the concept of verisimilitude. Whatever the logical difficulties in the concept, it is conceived in the spirit of Evolutionary Epistemology and derives its fruitfulness from evolutionism. In Popper's Evolutionary Epistemology, progress is seen primarily as an increase in universality. Popperian philosophy of science, in connecting the growth of knowledge to organic evolution, offers in this way a new basis for the history of science.