Whether or not it was especially prevalent, at least a few Pharaohs of the Ptolemaic dynasty married their sisters and produced offspring with them. What were the origins of the practice? Did it have any long term health effects on their offspring and the dynasty itself? And since the incest taboo is almost universal, how did they justify it?
I think this thread and the comments that I embedded as links should pretty sufficiently answer your question
Well first off the Ptolemaic dynasty was founded from Ptolemy, one of Alexander the Great's fellow generals. If you know that after Alexander's death the Macedonian kingdom split into three kingdoms. Ptolemy being the one that controlled Egypt. Ptolemy the general wanted to connect with the people in Egypt. So instead of forcing them to change their culture to Hellenistic(Greek) he adapted the Egyptian gods and culture. And to adapt their culture he married his son and daughter together(A long time Egyptian tradition was incest to keep the bloodlines "pure"). This led to it being a regular tradition for the Ptolemaic dynasty.
This is my first time posting here so please feel free to tell me if i broke any rules. Also /u/robwithoneb you can pm me if you have more questions.