In 1899, he authored a book entitled "The Races of Europe: A Sociological Study", which had grown out of a series of lectures he had given at the Lowell Institute at Columbia in 1896. Like many Americans of his time, at every level of education, Ripley believed that the concept of race was explanatory of human difference. Even further, he believed it to be the central engine to understanding human history, although his work also afforded strong weight to environmental and non-biological factors, such as traditions. He believed, as he wrote in the introduction to "Races of Europe", that: