Catlady's thoughts on wizarding population

[Mikael Raaterova]

No: HPFGUIDX 83189

Catlady wrote:

>In my own theory, is only partly a matter of Muggle genetics
>but also partly magical, with some deep magic causing that the number
>of magic babies born equals the number of mages who die, so that
>number of Muggle-born wizards has nothing to do with the number of
>Muggle births, but only with the excess of wizard deaths over wizard
>births.

While this is certainly possible, I feel uneasy about such essentialistic 
mechanisms. How did this death-birth balancing act come about? Who or what 
instituted it? What maintains it? How did the initial population of wizards 
come into existence, if the number of wizards is fixed?

I realize that I'm not quite sure what you mean. Are you saying that 
wizards are always are born to muggles in enough numbers to cover up any 
deficit of wizards due to more wizard deaths than wizard births? That would 
mean that the wizard population can't shrink. We'd get a population of 
wizards that becomes larger whenever the number of wizard births exceeds 
the wizard deaths, but never shrinks, because any deficit would be 
compensated with muggle-borns. Or do you mean that wizard births can never 
exceed the number of deaths, e.g. a wizard has to die before a new one is 
born? If so, then reincarnation could explain the effect you are 
describing. Of course, it leaves the small matter of how to explain how the 
initial wizards came about...


>the wizarding folk have never, in the
>last 3000 years, had a birth rate up to replacement level, because
>many wizards and witches never bothered with marriage and/or
>child-bearing at all.

I agree with your explanation for a low fertility rate -- witches are 
surely in control of their own fertility -- but I don't think it can be 
below replacement level, and definitely not for millennia. If it was, how 
would the pure-bloods avoid ever-dwindling numbers when they can't marry 
muggles or half-bloods if they are to remain pure-blooded, and when every 
pure-blood that decides to marry a half-blood or a muggle further decimates 
their numbers?

To be fair, new pure-blood lineages will come into existence, and if it 
only takes, say, four generations for a lineage to become pure-blood (e.g. 
Harry's children would be pure-bloods if he married a witch that was not 
muggle-born herself), the generation of new pure-bloods might compensate 
for the decreasing number of pure-bloods in every generation, depending on 
a) exactly how much below replacement level the pure-bloods' birth rates 
are and b) how large a fraction of pure-bloods that marry muggle-borns or 
half-bloods (sadly, I'm not good enough at demographic modelling to even 
try to determine this). Incidentally, there is a canon reference on the 
*upper* limit of generations needed to be considered pure-blood: Ernie 
MacMillan says that "you can trace my family back through nine generations 
of witches and warlocks and my blood's as pure as anyone's" (CoS, p. 150, 
UK pbk). To further compound the problem for the pure-bloods: once their 
numbers start to decrease, the rate of decrease will probably be 
accelerating. Diminishing numbers of pure-bloods make it harder for them to 
find an appropriate marriage partner, forcing the left-outs to either 
remain childless or have children with non-pure-bloods. The next generation 
will be even fewer (since we assume that birth rates are below replacement 
level) and thus sparser, making it even harder to find a suitable 
pure-blood partner but easier to find a suitable non-pure-blood partner, 
since the supply of potential non-pure-blood partners increases as the 
proportion of pure-blood wizards in the wizarding population decreases. So 
a larger fraction of the pure-bloods in this generation will choose 
non-pure-blood partner than the pure-bloods in the earlier generation did, 
causing a larger reduction in pure-blood births. Iterate until there are no 
more pure-bloods. A similar logic goes for the generation of new pure-blood 
lineages. While the proportion of pure-bloods is large, the probability 
that random pairings over X generations will produce pure-blood wizards is 
relatively large, but as pure-bloods become fewer, the probability of 
randomly produced pure-bloods decreases.

Wow. That was long and convoluted. Anyway, to try to conclude this: if 
wizarding birth rates have been below replacement level for millennia, one 
needs to explain why there are still pure-bloods.

/ Mikael