This monograph deals with the philosophical approach of thirteenth-century masters to concrete, practical manifestations of 'quantum ad naturalia' in human lives in their commentaries on Aristotle’s works on natural philosophy, both his genuine works and those then considered genuine. It inquires into what they deemed worthy of philosophical debate regarding this topic and how they tackled it. The first of the two volumes describes the cultural surroundings, the scholars’ way of approaching the topic, and their discourses on the peculiarity (singularity, unity, consistency) of humankind and on its internal differentiation according to gender, stage of life, social stratification, and differences due to ethnic status or geographic (climatic) diversity. This is the first comprehensive source-based study of the subject; it draws heavily on unedited texts.