The philologist and anthropologist, Friedrich Müller, used Haeckel's concepts as a source for his ethnological research, involving the systematic comparison of the folklore, beliefs and practices of different societies. Müller's work relies specifically on theoretical assumptions that are very similar to Haeckel's and reflects the German practice to maintain strong connections between empirical research and the philosophical framework of science. Language is particularly important, for it establishes a bridge between natural science and philosophy. For Haeckel, language specifically represented the concept that all phenomena of human development relate to the laws of biology. Although Müller did not specifically have an influence in advocating Haeckel's embryo drawings, both shared a common understanding of development from lower to higher forms, for Müller specifically saw humans as the last link in an endless chain of evolutionary development.