In his publications and teachings, Jacobus emphasized the importance of a scientific method of using primary sources in genealogical research. This replaced the idea of oral traditions and acceptance of time-honored pedigrees as facts due to their age. He provided the first basics of proper documentation and citation for all genealogists. While he endorsed the concept of eugenics he felt it was seriously lacking in the ability to properly trace bloodlines nor were those proponents of the field experienced enough in genealogical research or ability.