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.

LEARN MORE

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To learn more about this topic, 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

CREDITS

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Script Writer: David Goldenberg Script Editor: Kate Yoshida Video Illustrator: Ever Salazar Video Director: Emily Elert Video Narrator: Emily Elert With Contributions From: Henry Reich, Alex Reich, Peter Reich Music by: Nathaniel Schroeder

MinuteEarth is produced by Neptune Studios LLC https://neptunestudios.info

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REFERENCES

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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)