Thanks to 23andMe for sponsoring this video! Male birds have the largest genital diversity of any class of animals because their sex chromosomes make it easy to pass male-helping mutations down the line. Thanks also to our supporters on ___________________________________________ To learn more, start your googling with these keywords: Sex chromosome: A chromosome involved in determining the sex of an individual. Cloaca: A posterior orifice that serves as the only exit for the gastrointestinal, urinary and genital tracts. Mutation: An alteration in the DNA sequence that makes up a gene. Sexually-selected Trait: A trait based on a mutation that confers a reproductive advantage. BMP4: A protein whose presence halts the growth of bird penises in the egg. ___________________________________________ If you liked this week’s video, you might also like: An article from The Week about some of the strangest penises in the animal kingdom: _________________________________________ Subscribe to MinuteEarth on YouTube: Support us on Patreon: And visit our website: Say hello on Facebook: And Twitter: And download our videos on itunes: ___________________________________________ Credits (and Twitter handles): Script Writer: David Goldenberg (@dgoldenberg) Script Editor: Kate Yoshida (@KateYoshida) Video Illustrator: Ever Salazar (@eversalazar) Video Director: Emily Elert (@eelert) Video Narrator: Emily Elert (@eelert) With Contributions From: Henry Reich, Alex Reich, Peter Reich Music by: Nathaniel Schroeder: ___________________________________________ References: Brennan, P. and Prum, R. (2015). Mechanisms and Evidence of Genital Coevolution: The Roles of Natural Selection,Mate Choice, and Sexual Conflict. 1-21. Cold Spring Harbor Perspectives in Biology. Retrieved from: Brennan, P. (2013). Genital Evolution: Cock-a-Doodle-Don’t. Current Biology. R523-R525. Retrieved from: Brennan, P., Birkhead, T., Zyskowski, K., van der Waagand, J., and Prum, R. (2008). Independent evolutionary reductions of the phallus in basal birds. Journal of Avian Biology, 39: 487-492. Retrieved from: Briskie, J. and Montgomerie, R. (1997). Sexual selection and the intromittent organ of birds. Journal of Avian Biology. 28: 73-86. Retrieved from: Herrera, A., Brennan, P., and Cohn, M. (2014). Development of Avian External Genitalia: Interspecific Differences and Sexual Differentiation of the Male and Female Phallus. Sexual Development. 9: 43-52. Retrieved from: Reinhold, K. (1998). Sex linkage among genes controlling sexually selected traits. Sexual Selection. 44:1-7. Retrieved from: Image Credits: Mandarin Ducks - Francis C. Franklin Gorillas - Based on photo by Wikimedia user No escape Lake Duck Penis - Kevin McCracken (Published in Nature 2001)