Egyptians believed that the Pharohs were descended from gods. They practiced line Breeding techniques to keep the line pure. Line breeding was the norm not the exection and it continued through to the time of Cleopatra.
Racial Purity
The Egyptians believed that the first Pharaoh was born of Isis and was a God himself. The whole ruling structure of Pharaohs, Priests and Administrators saw themselves as “Gods”. They were determined to retain their racial purity. This meant that they did not inter-marry with their subjects. They indulged in “line breeding” a technique still used today when dealing with thoroughbred animals. Contrary to popular belief if managed carefully it reinforces desired characteristics and limits disease and genetic aberration.There are surprisingly detailed records of how the Egyptians kept the bloodline of the gods as pure as possible.
Line Breeding
Brothers married sisters, uncles married nieces. Line breeding works as long as any undesirable traits are identified and eliminated. this means that those with undesirable traits were removed from the succession and prevented from breeding. In some instances this meant death. The records show that this did in fact happen. Once this undesirable traits have been removed, which may take many generations, it is important not to bring in new genes from outside of the controlled breeding pool. Every new gene pool introduced may then take addition generations of monitoring to eliminate any undesirable traits. Understandably the priests in charge of the breeding program were very careful to the introduction of untested gene pools.
Creation
The story of the first Pharoh’s relation to the gods is a summary of the mystery of creation, of endless time and the unification of multiple deities. There seems to have been an attempt in the breeding programme to emulate as closely as possible the mystery of the genealogy of Isis herself. So much time and effort was put into the control of the breeding program that we can assume that if a Pharaoh took a partner who appeared to have no pedigree it simply meant that the person in question was introduced from a secondary level, less well documented. Even this occurs infrequently.
Women’s rights
All inheritance rights, including the right to rule, came through the mother who then with the guidance of the Priests, chose her partner. Perhaps because of this the Egyptian state was notable for its worship of goddesses and its reputation of treating women as the equal of males.
A good general article on Linebreeding ( but referring to dogs)
http://www.westwindgsps.com/linebreeding.htm
A wikipedia article which specifically mentions Egypt. Note that the Habsberg problems were due to uncontrolled imprecise inbreeding.
http://en.wikipedia.org/wiki/Inbreeding#Royalty_and_nobility