Sagan discusses the story of the Heike crab & artificial selection of crabs resembling samurai warriors, as an opening into a larger discussion of evolution through natural selection (& the pitfalls of intelligent design).

Image credit: PBS

The topics include the development of life on the Cosmic Calendar & the Cambrian explosion; the function of DNA in growth; genetic replication, repairs, & mutation; the common biochemistry of terrestrial organisms; the creation of the molecules of life in the Miller-Urey experiment; & speculation on alien life. In the Cosmos Update ten years later, Sagan remarks on RNA also controlling chemical reactions and reproducing itself and the different roles of comets (potentially carrying organic molecules or causing the Cretaceous–Paleogene extinction event).

YouTube video of Cosmos 2 by agarthas888