How The Pharaoh Was Chosen
The pharaoh was chosen in many different ways. Sometimes the son of the pharaoh's more favorite wife was chosen while other times the sons of lesser ranked wife were chosen. Many pharaohs married their own sisters, half-sisters, and sometimes even their daughters to keep the royal family running. If the Pharaoh had no sons, he would have to appoint the throne to a relative.
This is the Pharaoh Hatshepsut. She ruled from 1473 B.C.E to 1458 B.C.E. She was one of the only female pharaohs to rule over Egypt when her son wasn't old enough to rule himself. Usually when this happens the mother will rule until her son is old enough, but Hatshepsut ruled her whole life. She also sometimes dressed as a man to get the full power as male pharaohs did.
Relation to the Modern World:
Many countries, especially in Europe, still have kings or queens that pass on their titles to their children. To the left is a chart of the British royal family showing how the title was passed down until now.