In this episode we dive into Chapter 8 from Darwin's Descent of Man. James incorrectly attributed this chapter to the end of Volume I of the two volume set but it is actually the first chapter of Volume II, which makes more sense given its dramatic shift in focus and topic. Sarah tried to get us to differentiate between adaptive traits that come about from sexual selection with those that come about from natural selection. Photo from https://rollingharbour.com/2017/02/14/bluehead-wrasse-private-life-laid-bare/ We spent some time discussing the difference between sex-linked traits, like calico cat color, and sexually selected traits like the giant antlers on the extinct Irish Elk. James presented just a few hypothesis that have been proposed to explain female choice of traits and why those traits that females seem to prefer are often opposed by natural selection. It is hard to be a red male cardinal in the dead of winter. Sarah suggested interested listeners read The Evolution of Beauty by Richard O. Prum to learn how to differentiate the products of sexual and natural selection. We had a robust discussion about sex and gender and what Darwin knew at the time and what he should have acknowledged about the lack of binary distinction in the sexes. Mark realized he misspoke when he said that the rate of disorders of sexual development are around 10%. Data suggests that it occurs more like (1:2500–5000 live births) whereas gender dysphoria is reported to occur around 0.002-0.014%. The bluehead wrasse is a wonderful organism that challenges the simple-minded view that your sex is determined at birth. https://www.bbc.com/news/av/uk-northern-ireland-45449128 Sarah also encouraged us to watch some Green Porno to learn more details about the sex lives of non-human animals. You can see it here The opening theme to Discovering Darwin is "May" by Jared C. Balogh. http://freemusicarchive.org/music/Balogh/Revitalized_Eyes/MAY Interlude music is Alberta Hunter singing My handy man ain't handy no more from her Amtrak Blues album.