Here is a question about this article: Waitz defined anthropology as "the science of the nature of man". By nature he meant matter animated by "the Divine breath"; i.e., he was an animist. Following Broca's lead, Waitz points out that anthropology is a new field, which would gather material from other fields, but would differ from them in the use of comparative anatomy, physiology, and psychology to differentiate man from "the animals nearest to him". He stresses that the data of comparison must be empirical, gathered by experimentation. The history of civilization as well as ethnology are to be brought into the comparison. It is to be presumed fundamentally that the species, man, is a unity, and that "the same laws of thought are applicable to all men".
What is the answer to this question: What did Waitz stress that the data of comparison must be?
empirical