German anthropologist; known as the father of German anthropology. Extensive expeditions to many "exotic" parts of the world. Laid the groundwork for what would later become diffusionist anthropology, an important influence on Franz Boas. Bastian formulated the "principle of the psychic unity of mankind", which states that human kind is a single species, and that cultures differ for social, rather than biological reasons. This principle formed the foundation of comparative anthropology, in 19th century evolutionism (where it was taken up by prominent British evolutionists such as Tylor), and later.