Claude Lévi-Strauss published "Totemism" in 1962. In this book he says that totemism is a way that humans tend to classify people into similar groups. Once a population has made rules like exogamy (marrying outside the group) it becomes important to keep the clan different from others. But humans themselves do not have different features like wolves or birds do, so giving the identity of an animal to the clan makes its member distinctly different. This makes social boundaries.