Darwin, Charles Robert. The Origin of Species. Vol. XI. The Harvard Classics. New York: P.F. Collier & Son, 1909–14; Bartleby.com, 2001.www.bartleby.com/11/.
Lynch, Michael and O'Hely, Martin (2001) "Captive breeding and the genetic fitness of natural populations." Conservation Genetics. Kluwer Academic Publishers, the Netherlands.
Reuters. "Battery Farm Chickens Too Fat, Too Tired to Walk: Study." ABC News. ABC News, 7 Feb. 2008. Web. 16 Feb. 2013. <http://www.abc.net.au/news/2008-02-07/battery-farm-chickens-too-fat-too-tired-to-walk/1035272>
By Anthony Nguyen