1) The documentary follows Spencer Wells as he travels to Africa to trace the origins of humans through DNA evidence. All humans originated from the same tribe in Africa and share a common ancestry. 2) Early humans began migrating out of Africa for various reasons like climatic changes. They spread throughout Africa, Asia, Europe, Australia and eventually the Americas. 3) In 535 AD, a major global catastrophe caused by a volcanic eruption led to intensely cold conditions worldwide for two years, devastating many living creatures.