His more controversial theory is that the Tsimshianic-speaking peoples, Haida, and Tlingit represented the most recent migration into the New World from Siberia. He believed that their ancestors were refugees from Genghis Khan's conquests, some as recently as a few centuries ago. In works such as the unpublished "Migration Series" manuscripts, the book "Alaska Beckons," and numerous articles with such titles as "How Asia Used to Drip at the Spout into America" and "Buddhist Dirges on the North Pacific Coast," he eventually antagonized many of his contemporaries on this question. His thesis has been discredited by analysis of linguistic and DNA evidence.