[HPforGrownups] Digest Number 3878

[Mikael Raaterova]

No: HPFGUIDX 83065

Robert Shaw wrote, in reply to me

> > I have to disagree. Populations don't change overnight. The only
> > population-affecting event in recent history that we know about
> > is Voldemort's reign of terror.
>
>For these purposes, the 1890's are recent history.

Yep.


>The muggle population structure is still showing the effects of
>WWII, fifty years later.
>
>Given their longer lifespans, the wizarding population will
>be directly affected by events as far back as 1875-1900.

While the population *structure* and age distribution still shows the 
effects of the cohort-affecting events of WWII, AFAIK the deaths of WWII 
and post-war baby-boom didn't affect the population trend, e.g. aggregate 
growth, in any significant way (I'll admit I'm a bit hazy on WWII's 
population effects in the British isles, so I'm prepared to be proven 
wrong; data from 1950 onwards shows only steady increase though).


>Furthermore, since a significant proportion (currently about
>25%) of wizards are muggle born, any change in muggle
>demographics will have a knock-on effect on wizard
>demographics.

Changes in muggle numbers have to be *huge* to affect the number of 
muggle-born wizards. If we ignore post-OWL dropouts, then 36 muggle-borns 
enter Hogwarts per year (in present years), if 25 % of students are 
muggle-borns. That isn't a lot given a muggle population of 64 million in 
the British isles. That number should mean about 768 000 muggle births/year 
(if a year's births in proportion to total pop is comparable to Sweden's 
0,012 for recent years), or one wizard-to-be child in 21 000 muggle births. 
Even if post-OWL dropouts are up to one third of 6th and 7th year students, 
it's still only one such child in 20 000 muggle births. Granted, the muggle 
population has grown a bit over a hundred years, so the generational 
proportions of muggle-borns should be lower in the older generations and 
higher in the younger generations. Even so, if 75 % of present Hogwarts 
students are muggle-borns, it only amounts to about 100 magical births to 
muggle parents per year. Anyway, it's reasonable that the vast majority of 
muggle-born wizards are still relatively young, and that muggle-borns will 
outnumber wizard-borns in the foreseeable future.

Also, I see no reason at all to speculate about changes in the rate of 
births of wizards-to-be in the muggle population since there's absolutely 
no hint of it in canon. Having them be a constant fraction of muggle births 
seems instead a reasonable assumption.

BTW, is there a reference for the 25 %? I haven't come across that very 
interesting figure.


>The wizardly birth rate fall may be within wizardly living memory.
>The muggle birth rate fall certainly is, which has consequences.

It's highly unlikely the wizarding birth rates have fallen within living 
memory, unless mortality rates fell at roughly the same time. Seriously. 
Every year of low mortality and high fertility quickly adds up to enormous 
numbers. If the wizarding world enjoyed, say, 200 years of 5 % yearly 
growth (most industrializing countries had or have similar or higher growth 
rates while mortality rates were low fell until fertility fell) an initial 
wizarding pop of 1000 would be a horde of over *17 million* after 200 
years.  Rather, I'd say that the wizarding world has had low mortality and 
low fertility for ages, if not forever.

I note that you snipped my proposal for why the WW has had such low rates. 
Oh well. It seems eminently reasonable that wizards have enjoyed lower 
mortality rates than muggles since the ancient past. Potions for various 
maladies and and protective spells go a long way to fend off accidental, 
natural deaths. With their magical power combined with house-elf or muggle 
labour, wizards shouldn't need to worry about famine or back-breaking 
drudgery in the fields, and thus few deaths to malnourishment, relative to 
the muggles. Given lower mortality rates than muggles, wizarding fertility 
rates *must* have been comparatively low as well, or wizards would quickly 
out-grow the muggles.

If you don't accept a fairly stable wizarding population, you'll have to 
posit that they have had periods of low mortality and high fertility 
followed either by cataclysmic extermination events or equal periods of 
population decline. I think you'll have trouble finding causes for such 
changes.


>Quite simply, deductions from the student population of Hogwarts
>are only valid if nothing has changed for an entire wizardly
>lifespan, but we know the muggle-born wizard population must
>have changed significantly in just the last fifty years, a
>comparatively short period.

As a conclusion and summary to my points above, it's reasonable to assume 
a) that the wizard-born wizarding population have been stable for ages, and 
b) that the proportion of muggle-born has been increasing steadily as a 
function of the muggle population growth (only huge changes in muggle 
population can produce significant changes in the number of muggle-born 
wizards). Thus we should be quite able to deduce quite a lot from the 
number of students at Hogwarts.

And, by the by, UK's population has increased by 20 percent during the last 
50 years, which should correspond to an even greater increase in the number 
of muggle-born wizards since they are likely to live longer than muggles. I 
definitely agree that the muggle population explosion *is* a huge change, 
but it's effects haven't reached full strength yet, since muggle-borns are 
as of yet only 25 % percent of the total wizarding population. I don't have 
UK cohort data with which to calculate the likely age structure of 
muggle-borns and thus I can't calculate the likely proportion of 
muggle-born students at Hogwarts.


/ Mikael