21 reactions | This week's video on human evolution wraps up our unit on evolution and biodiversity. Our hosts, Sammy and Mini, taught us about natural and artificial selection, why humans have different skin colors, different ways we define species and how we classify organisms. And we had A LOT of fun along the way! Next week we start zooming-in on the building blocks of life on earth. Join us on YouTube with Crash Course and @crashcourseenespanol! | CrashCourse | Facebook