Hank describes the five factors that explain changes in allele frequency, which are at the heart of how and why evolution happens. The five factors he describes are: natural selection, sexual selection, mutation, genetic drift, and gene flow.
Peter gets home after being bitten by a genetically-engineered spider during a school field trip. He falls ill from the spider's venom, and while he's asleep the venom alters his genetic makeup. He wakes up to find his body has changed dramatically overnight.
Sophie tackles the question of why there are so many different breeds of dogs. She briefly discusses the history of dogs and discusses how genetics makes dogs different and why some breeds are better suited for certain functions.