The Medical News, 23 October 2006 Archived 10 February 2011 at the Wayback Machine Sommer, Volker & Paul L. Vasey (2006), Homosexual Behaviour in Animals, An Evolutionary Perspective.
The Medical News, ngày 23 tháng 10 năm 2006 ^ Sommer, Volker & Paul L. Vasey (2006), Homosexual Behaviour in Animals, An Evolutionary Perspective.