Do you have magic in your setting?
Does that magic have a genetic component?
Okay, bad news, you’ve justified eugenics.
It isn’t quite that absolute but you have to remember the gap between magically enabled humans and non magical humans is kind of categorically vast. There are ways around it, but in the default context, where magic is a thing that people can do that provides immense results compared to an individual human’s, a system of magic where a person’s genetics can influence it is a pretty easy to justify outlay for actual literal eugenics.
In the real world, setting aside eugenics’ moral or ethical framings, part of what helped to undermine it was the fact it just didn’t work. The people who believed in it weren’t receiving any inherent advantage due to their breeding, and it was kind of notable that no matter how well bred you were, it didn’t take many muddy peasants to pull you out of your castle by your feet and kill you. Eugenics is a fairy story in the real world, where a real true thing (we can change gene expressions in population through selective breeding) gets refined to a point of nonsense (we can lay out the genes of an individual like we’re picking out baby drapes). It’d be nice if eugenics failed just because of the moral reasons, but it turns out that there are lots of immoral things that get to persist despite that. Eugenics was, and is (hi there, Musk’s weirdoes) a fairy story privileged people tell themselves to justify the immense unfairness of the world.
The fact is, humans exist within such boundaries of capabilities that even the best of the best at things are not that far beyond what other humans can do, and often, the peaks of performance come at the expense of immense training regimes. Olympians live in food jail, pro wrestlers are extraordinarily good at performance and pain, and researchers specialise within their fields, and none of them mean that any one person is capable of just exceeding other people without infrastructural support. The best of the best are individually very intimidating but enough hands throwing enough bricks can make the differences disappear.
In the context of a magical setting, though, where you have individual mages capable of exerting immense force, force beyond a single human’s ability, or even a dozen human’s abilities, in first-order strategies like ‘can throw fireballs’ or ‘can fly,’ then suddenly the ability to breed that ability more commonly into a community represents a very meaningful incentive, and it seems like the kind of thing where, given enough time, the idea taking root and being acted on are kind of inevitable. This is obviously, a bad thing. Magical prowess being inborn and genetically predictable seems to directly represent a powerful incentive to begin mass producing People Of Mass Destruction.
Of course, this can be a bit of a bummer for settings to give up. After all, institutions and social structures give you a lot of stuff to work with for characters, and we have them in our world, so they can work as useful parallels. Magical colleges that pick up kids in their early tween years so you can have adventures learning magic in a school setting don’t necessarily have the same tools if there’s a hard rule that no, there’s no genetic bias or predisposition to magic, because at that point it can feel like there’s no institutional capture at work.
Alright, then what are some alternatives?
- Internal Control, External Power: Sure, you can breed the best wizards possible, but they’re all only just drawing on the magic in an area. Two wizards having a duel are chucking the magical energy of an area at one another, and adding a third wizard to the mix reduces the amount of power they both have by about a third. Wizards aren’t something societies can marshall in opposition to one another because every army just fields a few dozen really crap wizards that suck up the bulk of the resources in the area.
- Magic Alters Genetics: Wizards do have altered genes, but it’s the magic that they use that alters them. Kids of wizards wind up weird and all, but it’s not necessarily ‘magically weird’ as much as it is they’ve been subjected to a kind of radiation. Kids of wizards are therefore worth tracking and observing (in say, wizard colleges), but they aren’t necessarily going to do better magic than their parents, and they might just ber weird in other ways.
- Magic As Unlock: In a setting where anyone can use magic, but you don’t want everyone using magic, consider the value of magic not as a sort of can-you-roll-your-tongue genetic quirk, but rather that magical access is something you can go your entire life without doing, and the longer you take to do it, the harder it gets to do. This lets you have a classical magic system where children learning magic at a ripe age is important, without completely shutting out any adults who want to get involved based on their ‘breeding.’
- Culturally Genetic Magic: Okay, you have your magical colleges and dynasties and the importance of family names of wizards and they belief in breeding and all that, but also, they’re just wrong. There are lots of persistent beliefs in the world that are based on completely afactual nonsense, after all, and institutions are really good at justifying their continued existence. Plus, if magic is a cultural practice, then institutions like this will create more and better wizards, just not for the reasons they claim they are.
Personally, I favour the two ideas of Magic as an unlock and a dose in areas of culturally genetic magic. Not every kid has the concentration and focus to open that door, but there are lots of reasons you might.
One fun thing to consider, by the way, if you’re the kind of tumblr-centered author who wants the push, the population of wizards in a given city according to the old 3e DMG is about .5% The population of Australia, according to the carer surveys, that are autistic, is about .5%.
Just saying, if people want genetic magic.