Many species show off their teeth as a threat, so where did humans get our friendly smiles? Hosted by: Hank Green SciShow has a spinoff podcast! It's called SciShow Tangents. Check it out at www.scishowtangents.org ---------- Support SciShow by becoming a patron on Patreon: www.patreon.com/scishow ---------- Huge thanks go to the following Patreon supporters for helping us keep SciShow free for everyone forever: Kevin Carpentier, Eric Jensen, Matt Curls, Sam Buck, Christopher R Boucher, Avi Yashchin, Adam Brainard, Greg, Alex Hackman, Sam Lutfi, D.A. Noe, Piya Shedden, KatieMarie Magnone, Scott Satovsky Jr, Charles Southerland, Patrick D. Ashmore, charles george, Kevin Bealer, Chris Peters ---------- Looking for SciShow elsewhere on the internet? Facebook: www.facebook.com/scishow Twitter: www.twitter.com/scishow Tumblr: scishow.tumblr.com Instagram: instagram.com/thescishow ---------- Sources: www.ncbi.nlm.nih.gov/pmc/articles/PMC4812820/ wolf.org/wolf-info/basic-wolf-info/biology-and-behavior/communication www.semanticscholar.org/paper/Smiles-when-sharing-Mehu-Grammer/87014648ba7aeb73a5343527e056334d2c0254be ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.437507 users.ox.ac.uk/~kgroup/publications/pdf/scharlemann_etal_2001_jeconpsy_smile.pdf

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