Although the scientific method, empirical observation, was painstakingly pursued by the best minds of the 19th century, the theistic conceptions through which the empirical data was filtered produced some pretty bizarre conclusions.
Careful observation of fetal development revealed God’s hand in the progression of the fish-like embryo through resemblances of primitive animal life to ape-like higher animals including non-white species until reaching the perfection produced by a Euro-American mother.
The Genesis creation story of mankind originating from an original pair led to the notion of polygenism which determined separate creations occurred for the lesser animals and non-white races, a belief that accommodated a moral acceptance of slave ownership.
I suppose one of the difficulties with establishing any sort of factual truth is no matter where one starts the information gathering, pre-existing ideas must begin the process. Keeping those premises flexible is the key, I guess.