Knowledge and attitudes towards humans and animals have changed over time. The search for what characterizes humans and makes them different from animals has been important from the start. In antiquity, Aristotle laid with his Scala naturæ, the foundation for anthropocentric thinking about animals. A fundamental difference between humans and animals is the leading principle. The church fathers appropriated Aristotle’s thinking, by which they further spread and strengthened hierarchical thinking in relation to animals in the western world. At the end of the first part of this two-part article, it is described how Montaigne (16th century) questioned again the hierarchic superiority of humans, whereas a few decades later, Descartes still viewed animals as purely mechanical constructions (cf. the bête-machine).