Por que os trouxas não são extintos?

Não precisamos discutir sobre aptidão reprodutiva para explicar isso.

Aqui no mundo real, a taxa de fertilidade diminui à medida que o padrão de vida aumenta. Até bem recentemente, a comunidade mágica teve um muito padrão de vida mais alto que os trouxas. (Indiscutivelmente, eles ainda o fazem!) Portanto, esperaríamos que sua taxa de fertilidade, historicamente, fosse semelhante à nossa taxa moderna.

A taxa de fertilidade britânica atual é de nascimentos 1.87 por mulher. Foram cerca de nascimentos 2.9 por mulher em um ponto dos 1960s; provavelmente foi maior ainda mais cedo, mas vamos considerar isso como um número razoável para a fertilidade trouxa e o número atual como proxy da fertilidade mágica. (Parece razoável, talvez até um pouco alto demais, com base no que sabemos dos livros.)

Suponha que, em média, uma em cada duas pessoas mágicas se case com trouxas; isso me parece uma estimativa um pouco alta, mas vamos por agora. Isso aumentaria o número de casais na comunidade mágica em 50%, por exemplo, se a taxa de natalidade fosse exatamente 2 a eficaz taxa de natalidade seria 3:

Isso faz com que a taxa efetiva de nascimentos no 2.8, quase mas não exatamente mantendo a taxa nominal de trouxas de 2.9.

Obviamente, tudo isso depende de quais números você escolhe. Mas isso is plausível.

Termo aditivo:

Como PlasmaHH e Adam apontam nos comentários, a taxa de fertilidade não é realmente a melhor estatística a ser usada aqui, porque não leva em conta o número de pessoas que morrem antes de atingir a idade reprodutiva. No entanto, não acho que isso torne meu argumento implausível, apenas um pouco mais sutil: você deve levar em consideração que a fertilidade pode ser afetada por ambos taxas de mortalidade e padrão de vida.

(Em particular, não acredito que a taxa de mortalidade infantil tenha mudado o suficiente desde o 1960 para explicar mais de uma fração da queda na taxa de fertilidade no mesmo período, portanto esses números provavelmente ainda são bons o suficiente para estabelecer a plausibilidade.)

Pode-se esperar que o efeito das taxas de mortalidade na fertilidade se anule, deixando apenas o efeito padrão de vida como relevante. Parece razoável supor que as taxas de fertilidade ajustadas (contando apenas as crianças que sobrevivem para se reproduzir) possam permanecer diferentes o suficiente para contrariar a taxa de crescimento da comunidade mágica devido aos casamentos trouxas-trouxas.

Referências: este gráfico do Google com base em dados do Banco Mundial.

É muito possível que muitos "trouxas" apenas não sabia que eles eram bruxos.

O livro que admite estudantes para Hogwarts precisa de evidências concretas de uma criança usando magia antes de anotá-la como sendo aceita por Hogwarts. Esse livro foi colocado lá (e provavelmente criado por) pelos fundadores de Hogwarts.

Desde Hogwarts era fundada há pouco mais de 1000 anos atráse provavelmente um dos mais antigos (se não o mais antigos), antes disso, a única maneira de ensinar magia ou bruxa era por Educação escolar em casa, que ainda é usado na maioria dos países.

Portanto, a menos que uma criança nasça em uma família de bruxos que saiba que é bruxa, ela não aprenderá mágica. E com a família de um trouxa / um bruxo, os pais podem optar por nunca ensinar seus filhos a usar magia.

Pode até haver muito mais filhos nascidos trouxas do que os mostrados nos livros, mas porque eles não mostram nenhum sinal de habilidade mágica antes da idade de 11, eles nunca são selecionados para aprender a usá-la.

Portanto, dado que crianças fora das famílias bruxas só teriam sido informadas de que eram bruxas nos últimos anos do 1000, só haverá crianças crescendo em famílias bruxas aprendendo mágica. Isso limita severamente a população de magia real usando assistentes até cerca de 900AD, e mesmo isso é apenas na Grã-Bretanha.

Isenção, eu não sou aquele familiarizado com Harry Potter nem com um biólogo evolucionário, mas eu suspeitaria que os personagens se reproduzem através do sexo como seres humanos de verdade, então uma explicação fora do versículo seria uma explicação dentro do verso.

De um modo geral, a seleção natural que leva à especiação ocorre apenas na população de gargalos ou na população isolada (numeração na casa dos milhares). Essas populações são pequenas o suficiente para ter a característica / mutação presente na maior parte da população, antes da migração ou expansão.

Mesmo se falarmos de 4000 AEC, havia milhões de pessoas. Demais para uma pequena população de seres mágicos alterar geneticamente uma grande parte da população humana. De um modo geral, a maioria dos seres humanos não mora muito longe de onde nasceram, pode haver tabus culturais sobre casamento / reprodução fora de sua cultura. Todas essas coisas restringem o movimento genético.

Finalmente, ser magicamente confere um positivo à aptidão genética? Aparentemente, ser super forte e capaz de correr muito rápido pode parecer um positivo genético, mas pode significar que é preciso mais comida para me alimentar, ou eu morro em uma idade jovem, o que pode negar os positivos. Às vezes, melhorar a aptidão genética requer o que pode ser visto como uma regressão. Ou seja, cultivar cérebros menores devido à falta de comida, mas você vive para reproduzir ou desmoronar os camarões perdendo os olhos porque há pouco uso para eles e custa energia crescer e mantê-los.

Um conceito facilmente confuso sobre evolução é que a evolução não tem um objetivo ou objetivo final. Não está tentando selecionar as melhores características para criar a melhor criatura de sempre; é simplesmente selecionar a característica minimamente melhor que ajuda a criatura a sobreviver em seu ambiente atual.

A menos que ser mágico leve a pessoa a ser um amante prolífico, e com um bilhão de pessoas do 7 +, um amante muito prolífico, não vejo por que seres mágicos dominariam a população humana sem seleção artificial. Apesar um caso específico observar, embora a população afetada ainda seja pequena em geral e isso possa ser considerado um caso de seleção artificial via genocídio / guerra cultural.

Juntos, eu diria que, a menos que a autora decida colocar seu chapéu de biólogo e / ou antropólogo e realmente preencher a tradição, não há informações suficientes para descobrir por que exatamente o ser mágico não foi selecionado, dado o nosso conhecimento atual de como a evolução funciona.

Por que a magia pode não ajudá-lo evolutivamente em um exemplo superficial:

Digamos que haja três pessoas, uma com uma deformidade congênita das mãos, um humano "normal" e um humano mágico. Há um campo de bagas azuis que eles podem escolher para comer para cumprir sua ingestão diária de calorias (energia kJ). A pessoa com a condição da mão não pode colher o suficiente para se alimentar; ela morre antes que possa se reproduzir; a falha genética morre com ele. O ser humano 'normal' colhe frutos e vidas suficientes para se reproduzir. O humano mágico pega as bagas com um feitiço mágico e vive para se reproduzir.

Há poucas razões pelas quais a habilidade mágica seria selecionada sobre a habilidade "normal", em ambos os casos, ambos os seres humanos vivem para se reproduzir. A menos que a mágica o ajude especificamente a sobreviver e não apenas uma conveniência, haveria pouca pressão para selecionar por ser mágico. Isso seria especialmente verdadeiro no mundo moderno, se as pressões de coleta de alimentos e a sobrevivência contra predadores não estivessem tão presentes.

Só podemos especular, é claro, mas parece que ter magia te abre para um novo mundo de doenças e predadores que não afetam trouxas. Essa pode ser a razão pela qual eles não se tornaram dominantes, digamos, depois da praga negra.

Como exemplo, este é o classificação o Ministério propõe criaturas mágicas:

X: Chato

XX: Inofensivo / pode ser domesticado

XXX: assistente competente deve lidar

XXXX: Perigoso / requer conhecimento especializado / assistente experiente pode lidar

XXXXX: Assassino de mago conhecido / impossível de treinar ou domesticar

Nós trouxas certamente não precisamos desse tipo de classificação há muito tempo.

Um freio à população bruxa é a tendência dos trouxas de temer o que não entendem e de matar o que temem. E em uma sociedade primitiva "aquilo que eles não entendem" cobre uma quantidade bastante grande de terreno, de "tudo além da curva do rio" a "aquela velha idiota que vive na cabana na floresta, tudo por 'próprio'. E é uma curta caminhada, do ponto de vista do pensamento, da "velha burra" a "Bruxa!". E é uma caminhada ainda mais CURTA de "na cabana na floresta, tudo por si mesma", até o banquinho, até o tumbril, até "Antes de deixarmos a madeira acesa para queimar o mal de ti, bruxa, você gostaria de se arrepender de seus pecados ...? ". O próprio Tom Riddle empalideceria ao pensar em dez mil camponeses carregando tochas e forcados, batendo na porta do castelo ...! :-)

Há também o problema da equação de Zulu. Embora os mágicos tenham mais poder de fogo individual do que trouxas, um mago morto é tão morto quanto um trouxa morto. Como os britânicos descobriram na África do Sul, ter o dobro do poder de fogo do outro cara não torna cada um de seus soldados duas vezes mais poderoso - é mais como sqrt (2) vezes mais poderoso porque, como eu disse, morto está morto, e o cara que tem dois, três, dez ou 100 vezes mais poderoso que alguém está tão morto quando está morto. E, como o Exército dos EUA descobriu nas Filipinas, o cara armado com uma lança descendo a encosta da colina às vezes pode absorver seis rodadas de entrada (veja Revólver Colt M1892) e ainda sobreviver o tempo suficiente para plantar a lança bem no meio do peito. (O que levou ao desenvolvimento de uma arma lateral (o revólver Colt New Service) com poder de fogo suficiente para explodir grandes peças de lança).

Because magical powers are not an evolutionary advantage.

What matters is fitness, the ability to survive and reproduce, not "power", whatever that means. The dinosaurs were once the most powerful creatures on Earth, but their power didn't help them to survive when the meteor came. Rather, their size and strength became a liability when in the new landscape, and it was the much smaller mammals who survived and flourished.

Nothing we've seen about magical powers, and nothing you've said suggests that they would make Wizarding people any more fit to survive and reproduce than muggles. And, as you've acknowledged, they still reproduce at the same rates.

De acordo com esta ligação

Most wizards these days are half-blood anyway. If we hadn't married Muggles we'd've died out.

Let's accept that as true. Pure blood only would die out.

Muggle Wizard is more likely to produce a Wizard. This would indeed raise the Wizard population.

If a Wizard preferentially marries a Wizard they will not drive Muggle population to extinction. Wizards do preferentially marry within.

If the Wizards systematically married Muggles then the Wizard population would rise.

In summary Muggles are not extinct because Wizards tend to marry within.

I would place the blame on the wizarding community itself, which appears to have frequent power struggles between light and dark wizards. During Voldemort's reign of terror alone, a significant percentage of the British community was killed off. Such frequent infighting in a population would self-limit its growth through direct killings and also creating a negative environment that would discourage family formation and child-bearing to some degree.

This is definitely hard to explain. If the Wizarding community interbred with muggles for thousands of years, population genetics would definitely lead us to expect that most humans alive today would be magical, since everyone would have at least some magical ancestors.

I get the impression from the books that interbreeding was uncommon in the past, even though it's now common. That would make it possible for most people to still not have any magical ancestors. The rise of interbreeding means that will change in the future, and we should expect a large increase in the percentage of the population with Wizarding abilities.

The facts about heritability of Wizarding, as I understand it:

• Most children of two Wizard parents will be magical. (And no I'm not going to write Witch-or-Wizard everywhere. Please assume Wizard is a unisex term like Muggle.)
• Most children of Wizard + Muggle will be magical
• One Muggle parent doesn't make Squib offspring much (or at all?) more likely than for two wizard parents. (This is the most difficult part to explain with any kind of simple Mendelian genetic model.)
• Muggle-born witches and wizards are descended from Squibs who married Muggles; the magical ability unexpectedly resurfaces after many generations. (fonte).

A google search for harry potter population genetics turned up a high-school science lesson plan on heritability of genetic traits using Harry Potter characters and creatures as example, published by the U.S. National Library of Medicine. The end of the second lesson (pdf) proposes a theory of heritability of magical ability where magical ability is not expressed in Muggles because they carry at least one copy of a silencing version of a gene (allele) which regulates the activity of the allele for strength of magical ability.

Their theory explains some of the phenomena from the books, but not the low rate of Squibs / Muggles from Wizard + Muggle parents. (According to their theory, every Muggle has at least one copy of the genetically dominant silencing allele, so even in the best case, children from ss(wizard) + sS(muggle) have a 50% chance of inheriting an S (silencing gene) and being pure Muggle, with not even weak magical ability. Some Muggles would carry an SS genome and be incapable of ever producing magical offspring, so clearly this model doesn't match this aspect.

Traits caused by multiple alleles have more complex behaviour, but I suspect there might not be any purely Mendelian explanation. I think the fact that children of Wizard + Muggle are no less likely to be Squibs is the hardest thing to explain. Perhaps this is a case of unreliable narrators, since the characters saying this are fighting a war against pure-blood supremacists! (And out-of-universe, I think JKR didn't want her story to include a genetic basis for discrimination.)

Perhaps at this point, interbreeding is still a new thing, and Wizards almost always have two copies of the magical allele(s). Perhaps after some generations of mixing, Muggle + Wizard will have a significantly lower chance to produce magical offspring than Wizard + Wizard.

Or maybe it's magic. Fortunately, invoking magic to explain magic is not exactly a problem, but it means we can't just use formulae from evolutionary biology / population genetics.

The extreme heritability of Wizarding should make it spread much more easily / strongly than a normal genetic mutation. It will easily become fixado throughout a population as soon as a few Wizards are common ancestors of all living humans. (This happens after enough generations, even with limited interbreeding.)

O most recent common ancestor (MRCA) of all humans alive today may have lived as recently as a few thousand years ago. The existence of long-isolated tribes may push that number back as far as the Upper Paleolithic, but a few thousand years or even shorter is probable if we don't worry about isolated pockets and just consider the bulk of Western civilization (the setting for Harry Potter).

At some point before the time of the MRCA, there's a point where everyone in the population is either an ancestor of everyone alive today or has no living descendants.

However, if Wizards limit their interbreeding with Muggles, the populations could stay separate. Wizardlyness can't spread throughout the Muggle population because of the practice of removing Wizards from their Muggle parents and bringing them into the Wizarding world. At that point they no longer count as Muggles, and are more likely to marry (or whatever) other Wizards.

The un-expressed form (that leads to Muggle-born wizards) could spread throughout the Muggle population, but IDK what the implications of that are. IDK if it's normal that Muggle-borns can identify a specific Squib ancestor, or if some just happen from random chance (i.e. inherited from an ancient magical ancestor many tens of generations ago, i.e. magic is just circulating in the gene pool.)

Anthropological and genealogical reasoning aside, the numbers on this are actually pretty clear. There may be muggle-born wizards in the school, but from a population of many millions, any given year only has at most a few dozen.

Consider (for example) a sample size of 10000 muggles and 10 wizards. Let's say the chances of 2 wizard parents having a squib are 1:10. Let's also say the chances of 2 muggles having a wizard child are 1:10000. Even at a matched birth rate of 2.5 per couple (and dropping the previous generation), the result after 10 generations would be:

92966 Muggles Born, 9 Wizards born to Muggles, 46 Wizards born (including to muggles), 4 Squibs -- effectively multiplying the muggle population by 9.3 and the wizard population by only 4.6

Now let's tweak those ratios - 1:100 squibs and 1:1000 muggle-born. This results in: 91298 Muggles, 91 Muggle-Born, 924 Wizards, 8 Squibs

Suddenly, there are a whole lot more wizards, but even after 100 generations and tens of trillions of total people, there are 21.4 muggles for every wizard.

It would take 1:100 muggle-born (with muggle-born wizards in vast quantities) and 98 generations (as well as tens of trillions of people) before wizards actually outnumbered muggles, at 1:.999

With the actual numbers being even harsher than the initial example, the math holds up.

I consider there are quite a number of reasons for why the world is not dominated by wizarding population(and basically why I am a muggle :-( ):

1. Magic is not a skill that could be developed over time by training. You have to born as a wizard or a witch. And the chances of you being in the center of muggles is very high. In that scenario, even though you might realize you develop few powers, you will not know how to nurture it and grow it. Add a few more generations down the line, you might have muggle children succeeding you. Remember Trelawney saying that the art of prophecy might lose a few generations. What if the art of magic can be lost for an entire bloodline?
2. In the ancient times, people tend to live along with the "magicians" or "priests". So if you have the talent and if they train you, you can sustain those powers and be magical. If a no is on either of them, well, live as a muggle.
3. There could be civilizations of magical people living together in the past(Still thinking of Atlantis). That will be lot safer for the wizards and witches. But might have ended due to any of the natural calamities or diseases or any other reason that ends civilizations. In that case, the world will quickly turn into a more muggle population than wizarding.
4. There could be millions of people who born as magical but never found their powers at all and just died without using the power at all(you can call them Just Harry's). Not all people will have a Dinky Diddydums to chase them and let them experience their accidental magic.
5. In the medieval time, it was also became very common to burn witches and wizards. This might have reduced the populace even further.
6. Due to the medieval times, (I hope/guess) many wizards/witches started on the pure blood cr*p. Which just means, more magical people isolating from non magical, thus reducing the half blood children.
7. Hogwarts happened only a 1000 years back and so we can safely say that until then there is no centralized school that takes each and every magical children and train them. Instead, most wizarding families might have trained their children themselves and might not extended the same to any other muggleborns, if they ever found one.
8. Even now, magical people are still rare. Still Hogwarts kind of gets kids in only hundreds every year whereas it is a global school. Add Durmstrang and Beauxbatons to the mix as well and you will still find that the number might go up to a thousand or a little more per year. Muggles can beat that kind of population in minutes.

You don't just magically know all magic, you need talent and then have to learn it. An untrained Harry Potter without any guidance would not be significantly more likely to survive in a world where you can't just order pizza.

Discovering spells with no training without blowing yourself up is hard. Figuring out what a wand is, how to make it and having it happen to choose you is very unlikely to just happen. While magic without a wand is possible, it is much harder, especially for the untrained.

Having to hide magic from Muggles is not obvious and had to be learned the hard way. Writing books about magic (those moving images are not easy to make with just sticks and rocks) and figuring out effective ways to find and train young wizards took thousands of years, so in the early days there was just not much you could do with magic due to a lack of knowledge.

Also keep in mind that food was a major concern that took most of the population's productivity. After spending the day trying not to starve the amount of time and energy you had left to practice magic was near zero, so useful discoveries were rare.

TLDR: Just like science, magic had to be discovered in a slow and difficult process.

I offer a much simpler reason: the same reason pandas aren't. That is: people (specifically wizards, here) don't want to see them die off. It's the human nature of helping, which leads to people volunteering in third-world countries instead of letting them die off. No reason to hurt them, and they survive well enough alone.

For most of history, magical people have had superior power to Muggles.

This does not necessarily lead to Wizards out-breeding Muggles. On the contrary, it seems that having a better quality of life actually leads to a lower birth rate. Not by biological causes, but by choice.

So, your question is similar to asking why people in developed countries don't out-breed people in poorer countries, despite having superior technology. Actually, as it seems to be in our days, it's quite the opposite which is happening.

It is possible that the premises described simply do not necessarily lead to the conclusion in question.
For example, humans are considerably more powerful than most other forms of life on the planet.

This includes bacteria, molds, ants and many other types of insects, and a whole lot of other animals etc. Many of these were around long before humans, but there are newer species as well. Check out "The eight super-adaptable life-forms that rule our planet" for some examples; humans represent a small percentage of the population (and even biomass) compared to some of these. Inferior powers do not automatically lead to a wipeout, even long term.

Humans have the capacity to exterminate colonies of other species and even erradicar certain life-forms intentionally, and while we are now killing off a bunch of others, it's unintentional and many folks would strongly prefer we stop doing that. Intentional, systematic eradication in most cases simply does not provide marginal benefits greater than the marginal costs of doing so. This is true even for species we consider pests or which carry disease. Further, we don't necessarily understand all the follow-on effects that might occur following the loss of the "ecosystem services" that species currently provides. At least some things that Muggles build and do are useful to wizards, and that's an explicit disincentive to wiping them out, even before any ethical considerations come in.

1. Natural selection is not applicable to sentient species with society.

   Society (laws, standard of living, cost of living vs capita, religion, etc.) determines reproduction rate. Biologically 'superior' and mentally 'superior' in certain societies is not correlated and may be inversely proportional to reproduction rates. An exception to this is if you define 'survival of fittest' circularly such that those who survive are by definition more 'fit'. A circular definition would mean that for reasons perhaps not obvious, wizards are less 'fit' than humans. See 2. for such speculation.

2. The wizarding community is not self sufficent.

   Ron in Câmara de segredos:

   Most wizards these days are half-blood anyway. If we hadn't married Muggles we'd've died out.

   Wizards can have non-magical children (squibs). That combined with other societal factors (evil wizards, standard of living, cost of living, etc) may explain why wizards appear to be an anomaly as opposed to a norm in society.

The problem is in the question: Evolutionary advantage and natural selection are irrelevant unless there's direct competition. We don't find lizards extinct simply because they're less fit than monkeys. Nor do we find that one (color) race of humans goes extinct. Nor do we find blue eyes or brown eyes eradicated.

Neanderthals are likely extinct not because they were less adapted - in fact, from what I've read, they were generally more fit on the individual level. Their winning competitors grouped up (which in itself was the more relevant advantage) - but what's important is that they were probably murdered. By agency, not evolution. Similarly, the wizarding world would have to team up on and take out the muggle world by intention and force in order for their "power" advantage to matter or become relevant.

The other half that matters is simply geographic distances - competitive love instead of competitive war. The Mongols, for example, spread their seed very intentionally. But there's plenty of reason to believe, from the books, that the wizarding world (at least mostly) kept to itself. This propensity is far more important, even if it's only slightly less than that of muggles, than fitness. Again, if the fitness isn't a matter of direct competition, it has to be a social endeavor to spread out, which doesn't seem to fit with the wizarding culture.

So, again, evolutionary fitness and natural selection are totally irrelevant to the spread of the magical genes. Until there's a war between the two camps that seeks total annihilation, at least. (At which point, having magic may not counterbalance muggle ingenuity, cooperation, individual genius, sheer numbers, or technology.)