Thanks to 23andMe for sponsoring this video! http://www.23andme.com/minuteearth 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 https://www.patreon.com/MinuteEarth ___________________________________________ 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: http://theweek.com/articles/474417/12-weirdest-animal-penises-earth-updated _________________________________________ Subscribe to MinuteEarth on YouTube: http://goo.gl/EpIDGd Support us on Patreon: https://goo.gl/ZVgLQZ And visit our website: https://www.minuteearth.com/ Say hello on Facebook: http://goo.gl/FpAvo6 And Twitter: http://goo.gl/Y1aWVC And download our videos on itunes: https://goo.gl/sfwS6n ___________________________________________ 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: http://www.soundcloud.com/drschroeder ___________________________________________ 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: http://cshperspectives.cshlp.org/content/7/7/a017749.abstract Brennan, P. (2013). Genital Evolution: Cock-a-Doodle-Don’t. Current Biology. R523-R525. Retrieved from: http://www.sciencedirect.com/science/article/pii/S0960982213004430 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: http://onlinelibrary.wiley.com/doi/10.1111/j.0908-8857.2008.04610.x/abstract. Briskie, J. and Montgomerie, R. (1997). Sexual selection and the intromittent organ of birds. Journal of Avian Biology. 28: 73-86. Retrieved from: https://www.jstor.org/stable/3677097?seq=1#page_scan_tab_contents 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: https://www.ncbi.nlm.nih.gov/pubmed/25011524. Reinhold, K. (1998). Sex linkage among genes controlling sexually selected traits. Sexual Selection. 44:1-7. Retrieved from: https://link.springer.com/article/10.1007/s002650050508. Image Credits: Mandarin Ducks - Francis C. Franklin https://commons.wikimedia.org/wiki/File:Pair_of_mandarin_ducks.jpg Gorillas - Based on photo by Wikimedia user No escape https://commons.wikimedia.org/wiki/File:Gorillafamily.JPG Lake Duck Penis - Kevin McCracken (Published in Nature 2001)