"In the magic world, every little wizard is very precious."

Combining this sentence in the original book with the rare number of people in the British magic world, I speculate that in the magic world, a wizard's pregnancy is actually the result of the fusion of the magical powers of both parents.

The higher the degree of parental integration, the higher the possibility that the child will be a wizard, and vice versa, the child may be a squib, and may not even be able to give birth to a small wizard.

After the parents have successfully conceived the little wizard, their own magic power will be weakened, because wizards with high mana such as: Voldemort, Dumbledore, Grindelwald, McGonagall, Flitwick, Bellatrix, Snee Pu and so on have no children.

Therefore, the author assumes that the birth of the little wizard will take away part of the magic power of both parents.

Speaking of which, someone will definitely mention Molly Weasley and Bellatrix's final battle. Bella's high status among the Death Eaters in her early years shows that she is superhuman, but she was defeated in Azkaban. After being locked up for 14 years, her strength has been greatly reduced, and it is possible to have one more. Well, Rowling has given the villain a halo of wisdom.

And the bloodline theory actually makes sense. There are almost no pure hemp wizards with high magic power.