Chris Gowens, "Moral Relativism" is an entry in the Stanford Encyclopedia of Philosophy discussing the historical background and main arguments with extensive bibliography.
S.K. Sanderson, "Edward Westermarck:The Invisible Master" is a paper on the site All Academic Research presented before the American Sociological Association discussing the career and major contributions of Westermarck.
Chris Swoyer, "Relativism" is a short discussion from the Stanford Encyclopedia of Philosophy defining the difference between descriptive ethical relativism and normative ethical relativism.
Petri Liukkonen, "Edvard (Alexander) Westermarck" essays the life and thought of Westermarck with a bibliography of Westermarck's writings on the Books and Writers Website.