The Origins of the Wizarding World
As I've been reading and re-reading the Harry Potter books, I've found myself wondering how the wizarding world was first started. Were there always people who were naturally talented in magic who studied it night and day, through the generations, until it developed into what we have seen in HP? Somehow I don't think it was this simple.
In the Roman and Greek traditions, those who had magical powers had connections to the various gods and goddesses. Priestesses and Priests were thought to have powers including the ability to read omens and heal, but they drew these powers from the gods. Medea, who married Jason of the Argonauts, was also a powerful sorceress. Her abilities came from her grandfather, Helios, the sun god. Hercules' super-human strength came from his father, Zeus, Orpheus' great musical ability came from his father, Apollo, and so on and so forth. So it seems to me that there has to be more to witches and wizards than just pure talent.
We've seen other human-like creatures in the HP universe, such as dwarves, centaurs and giants. While none of these creatures shows quite as much of a flair for magic--though the centaurs come close with their mastery of divination--I do think such beings are the root of wizards and witches. Perhaps a human-like creature with magical powers (possibly a nymph, for example) married into the earlier races of man, producing children with magical abilities. Such children then worked on developing their talents and passed them on to their children.
At any rate, it is doubtful there were many witches or wizards early on. Some Native American tribes had their shamans, but they were rare. So in order for the wizarding world to become as populated and complex as it seems to be in HP, they must have (at least at first) kept marrying within other magic families. This is probably how the tradition of purebloods got started, since it was so important to early wizards.
If you look at the ability to perform magic in the terms of genes, this can account for why there are both non-magical people with wizard parents (squibs) and magical people with muggle parents. For example, if this ability is recessive, a witch and a wizard are pretty much guaranteed to have a witch or wizard as their child. Since squibs seem to be rare, I will assume that their presence in society is due to extremely rare mutations that result in the loss of magical abilities. This loss may be temporary, lasting only a generation or two, depending on who they marry; if they marry a wizard/witch, their children may very well be magical.
As for muggles having a wizard/witch for a son/daughter, it can be explained as follows. Long ago, if a witch/wizard married a muggle, they would have a muggle child. The recessive magic gene could be passed on and on for generations until two muggles with this gene married. Then, they would have approximately a one in four chance of having a child with magical talents. If there was enough time between the wizard/witch who married a muggle and the wizard/witch born to muggles, all in the same line, it would appear that people with absolutely no magical roots had magical children.
Also, if such a muggle with the recessive magic gene married a witch/wizard, that couple would have a fifty percent chance of having a witch/wizard child.
Continuing with looking at magic as the result of certain genes, we can easily see why a wizard or witch's family background has little to do with how talented they are at magic. As long as they have the correct genes, they have the ability, and how far they go with it probably has more to do with how hard they work at it (such as in Hermione's case). However, there are always some who have certain talents and can use them better than others without having to put as much effort into it (such as in Harry's case).
These are just some of my ideas on how humans were first able to use magic in HP. I hope I've taken enough into consideration; though this article is complete, I realize that the idea still has room to be reworked. I welcome any thoughts you might have on this theory, so feel free to email me in response.
Note: I apologize if any of my information is incorrect or if I've miscalculated genetic percentages.