Dr. Joseph talks about the genetic link between languages: that they have common origins. He focuses on European languages; Proceedings of the American Philosophical Society. Vol. 161, No. 1 (March 2017) pp. 15-24.
Andrew Garrett talks about lanugage diversity, specifically in Indo-European languages.; Proceedings of the American Philosophical Society. Vol. 161, No. 1 (March 2017) pp. 25-38.