The Muggle-Born Population

[danajsparks.livejournal.com]

In some interview, J.K. Rowling apparently said that Britain's wizarding population is roughly divided into 25% muggle-born, 50% half-blood, and 25% pureblood. However, while JKR may have said that 25% of witches and wizards are muggle-born, this is not what she has actually shown in canon.

In Harry's year at Hogwarts, there are only two confirmed muggle-born students in canon: Hermione Granger and Justin Finch-Fletchley. JKR's early class list also shows Hannah Abbott and Terry Boot as muggle-borns, but she apparently later either forgot this or changed her mind, for we learn in DH that some of Hannah's family is buried in a wizarding cemetery, and Terry was able to attend Hogwarts when Voldemort was in control. JKR originally imagined Harry's class as having 40 students, but only 30 students are ever mentioned in canon, and only 25 are mentioned elsewhere besides the sorting ceremony. 2 out of 40 students would mean that 5% of the class is definitely muggle-born. 2 out of 30 would mean that 6.66% is muggle-born. 2 out of 25 would make 8% of the class muggle-born. Any of these percentages is much lower than 25%.

(Note: Apparently I can't count, so I've had to change these percentages a few times. Hopefully they're correct now.)

Furthermore, (as far as I can remember) we only meet 3 other muggle-born students at Hogwarts: Penelope Clearwater and the two Creevey Brothers. And we only know of three muggle-borns from the previous generation: Lily Evans, Ted Tonks, and Dirk Cresswell. Again, these numbers suggest that the percentage of wizards and witches who are muggle-born is much lower than 25%

ETA: Oryx reminded me Add Mary McDonalds and the Mary who was on trial during the trio's Ministry invasion (though the two may be the same person, under her maiden and married names).

Another sign of a low percentage of muggle-borns is the WW's ignorance of muggle culture and technology. If muggle-borns were really 25% of the wizarding population, I believe that they would have had significantly more influence on wizarding culture. Wizards would have assimilated and adapted more muggle sports, muggle board games, film, television, etc.

The data I used for these calculations can be found here: https://spreadsheets.google.com/pub?hl=en&hl=en&key=0Asq6Ul6gdxBCdDlMRHoxU0NVaHA5SXQtQzRiRFI0Smc&output=html If the blood status is in parentheses, that means it was shown that way in JKR's notes, but unverified or contradicted in canon.

Comments

[lynn-waterfall.livejournal.com]

JKR probably wanted those numbers in order to present purebloods as a privileged minority. That's my theory, anyway.

If Muggleborns are only 8-10% of the population, then halfbloods and purebloods are a higher percentage, obviously. More than that, though: the fewer Muggleborns, the fewer halfbloods with Muggleborn parents. If you're going to have even 50% of the population be halfbloods, then (assuming family size doesn't vary according to blood status, averaged out), then...

Okay, if 10% of the population is Muggleborn, then assuming no Muggleborns marry Muggles or other Muggleborns, then means only 20% of the population would have halfblood children without marrying Muggles. That's 20% second-gen halfbloods with Muggleborn ancestry, whose children will be purebloods unless they marry someone with more immediate Muggle ancestry than their own. That would leave 70% of the population as purebloods.

If a lot of witches and wizards marry Muggles, then you get a higher percentage. Although I think that the only halfbloods with Muggle parents that we *know* of are Seamus, Dean (I guess, although it isn't book canon), Severus, and Voldemort.

Magical-Muggle marriages would produce halfblood descendants for two generations, minimum, so...

(gets headache)

Well, if another 10% of non-Muggleborns married Muggles, then that would produce as many first-gen halfblood children as the Muggleborns (call it 20x), and *those* children's children would produce an additional 20x halfbloods (or more, up to 40x, but they might well marry other first-gen halfbloods or Muggleborns, whose children would be halfbloods anyway). That would lead to at least 60x halfbloods total, or up to 80x. And only 10-30x purebloods.

(I'm really not a math person myself. I think I have to stop using percentages when suddenly there are more adults having children than the total WW population, but what do I know?)

Still, that's a high number of witches and wizards marrying Muggles. So, if only 5% of non-Muggleborns married Muggles, which sounds moderately reasonable, that could produce up to an additional 20x, roughly 40% of the population. Then the breakdown would be roughly 10% Muggleborn, 40% halfblood, and 50% pureblood, with a tendency for there to be a somewhat higher percentage of purebloods than that.

Does that sound at all reasonable? Feel free to pick apart my math or anything else, I'm just thinking "out loud."

[danajsparks.livejournal.com]

ugh, my brain hurts.

I don't know how to figure out the percentages of half-bloods and purebloods. I feel like there are too many uncertain factors.

First, the best definition we seem to have for "half-blood" is that a person has two magical grandparents.

If Severus married Lily, their children would have 1 magical grandparent.

If Severus married Narcissa, their children would have 3 magical grandparents

If Hermione married Justin, their children would still have 0 grandparents, but their grandchildren could easily have 4 magical grandparents.

If Hermione married Dudley, their children would have 0 magical grandparents, and their grandchildren would still have at least 2 muggle grandparents.

Second, we don't know anything about population growth in the WW, nor the birthrate among purebloods compared to half-bloods and muggle-born.

Third, we don't know how many muggle-born marry other muggle-born, half-bloods, or muggles, instead of purebloods.

I think it's probably safe to say that, while a majority of the population may technically be "pure," a significantly smaller percentage of purebloods have bloodlines that are completely magical for more than a few generations back.

[lynn-waterfall.livejournal.com]

Second, we don't know anything about population growth in the WW, nor the birthrate among purebloods compared to half-bloods and muggle-born.

Oh, absolutely. I had to assume that there was no difference in order to say anything.

Third, we don't know how many muggle-born marry other muggle-born, half-bloods, or muggles, instead of purebloods.

Also very true. I tend to think that when JKR came up with the ratios she did, she was probably figuring that most Muggleborns married someone who wasn't also a Muggleborn. (Or a Muggle.) If all Muggleborns marry non-Muggleborns, and no one in the WW marries Muggles, then the 25-50-25 fits perfectly. Even 1% of non-Muggleborns marrying Muggles produces 4x halfbloods, though.

I think it's probably safe to say that, while a majority of the population may technically be "pure," a significantly smaller percentage of purebloods have bloodlines that are completely magical for more than a few generations back.

Yeah. Even with Ernie's line in CoS, "you can trace my family back through nine generations of witches and warlocks and my blood’s as pure as anyone’s," that first part may only refer to one ancestral line after the three generations required to be a pureblood.

[danajsparks.livejournal.com]

Yeah, like, I can accept that the Blacks are quite pure, but I bet the Weasleys have some fairly recent muggle ancestors, even though the direct Weasley line is probably quite old.

[oryx_leucoryx]

Hem, Arthur's mother was a Black, so no. And one of Molly's uncles married a Black without her getting burnt off the family tree, so I doubt that, unless the Muggle component was on Molly's maternal line.

[danajsparks.livejournal.com]

But it's possible that Septimus's mother was a muggle-born or half-blood. After all, the Blacks Blasted Cedrella off their family tree for marrying Septimus.

[oryx_leucoryx]

Septimus was considered a blood-traitor. You can't be one without being pure-blood in the first place (or where would the treason be?).

[danajsparks.livejournal.com]

I was under the impression that the Weasley family in general were considered blood traitors, not specifically Septimus.

I thought the traitorous part might, in part, be that the Weasley men marry muggle-born or half-blood women every few generations in order to keep the line robust. After all, it's Ron who says, "Most wizards these days are half-blood anyway. If we hadn’t married Muggles we’d’ve died out."

[oryx_leucoryx]

I thought the traitorous part might, in part, be that the Weasley men marry muggle-born or half-blood women every few generations in order to keep the line robust.

IMO blood-traitor means a pureblood who has odd, non-traditional political inclinations. The Weasleys are just like the Blacks, but with red hair and no style.