One possibility here is that magic is controlled by a recessive gene. The same kind of random combination (or random mutation) that produces an occasional albino human (rare, but far from unknown) produces a specific variation on a neurotransmitter (or receptor) that gives control of magic.

Why hasn't this given an evolutionary advantage and swept through the entire race, making those without the gene vanishingly rare? First, it's recessive -- the "normal" dominant gene codes for production of a biochemical that the recessive variant fails to produce; and second, the recessive, while harmless when heterozygous, creates a condition of very low fertility (or even, effectively, sterility) when homozygous that greatly reduces the likelihood of the mage successfully reproducing.

As a result, while carriers of the gene are fairly common (like carriers of blue eyes in humans), because those who express the gene are virtually unable to reproduce, there is no chance of homozygous carriers producing lines of mages.

This could also be a multi-gene condition, where two or more recessive sites would have to combine to produce the "mage" variant neurotransmitter/receptor. This would make mages even rarer (instead of blue eyes, this would be more like polydactyly).

Using / accessing Magic is instinctive once you know how, but almost impossible to describe in a meaningful manner to someone who can't do it.

A "real world" equivalent would be wiggling your ears: Anyone can do it if they can work out how to isolate and move the correct muscles. And, once you can do it, you can just do it - and explaining it to someone who can't will seem annoying and frustrating. There are exercises that you can do to help "get the feel" for the muscles, but some people would take years of practice before it "clicks", and other people are effectively born with the ability.

Then, because of this initial "speedbump" that most practitioners need to get over, the Mages Guilds collectively claim that magic is not something that anyone "can just learn" - and regularly send around theatrical mystics to seek out suitable apprentices with claims that "they possess the rare gift". Some use it as an excuse to rescue the poor and downtrodden - others as a way to scam rich nobles (either into paying for lessons, or into paying for the mage not to take their child away!)

An inverted real-world example (i.e. where the "have-nots" are rare, and lack a skill that most take for granted) would be depth perception / binocular vision: There are people out there who don't develop the ability to use both eyes to judge how far away something is - everything the looks flat to them, like watching it on a TV screen or cinema screen. However sometimes, with a suitable stimulus, their brain "reboots" and they gain the ability - an example I have heard was someone who was taken to see a 3D movie (complaining that there was no point) and the over-done & exaggerated CGI 3D effect forced his brain to consider "something's not right here" and evaluate the image from each eye separately. So, next time someone wears 3D glasses and jokes about how it makes Real Life look 3D to them - they may actually have a point.

No formal training does not mean no training.

Consider barber-surgeons.
http://broughttolife.sciencemuseum.org.uk/broughttolife/people/barbersurgeons

Barber-surgeons were medical practitioners in medieval Europe who,
unlike many doctors of the time, performed surgery, often on the war
wounded. Barber-surgeons would normally learn their trade as an
apprentice to a more experienced colleague. Many would have no formal
learning, and were often illiterate.

You can formally train to use magic, as your healer probably did: colleges, competing schools of thought, theoretical basis and so on. The physicians in the Middle Ages had all of that. They also considered themselves above services like surgery or pulling teeth.

Then there are people like your weather witch. This is everyday magic and would have been learned as an apprentice. Probably your guy was a sailor first and the old weather witch on his ship saw he had potential and so started teaching him on the job. There can be other similar low level magic users - flea and louse killers, tinkers, sore tooth healers and so on. The formally trained magic users of course do not consider such to really be mages and a comparison would likely offend the one and embarrass the other.

If you look at the "real world", there are a lot of abilities that are available to everyone (or almost everyone), but most people don't have: skateboarding, juggling, doing handstands, or playing a musical instrument, to name a few. Let's take that last one as an example.

Anyone could pick up a trumpet or a clarinet and make a few hoots or squeaks - the magical equivalent would be a tiny puff of wind, or a slight shift in color, something that barely even registers on the senses. Trying too hard makes a loud BLAT or squeak - the magical equivalent of something locally annoying, like giving yourself terrible indigestion, or making the area around you smell of old fish.

After a few minutes toying around with what combination of keys produce what sound, you could probably play an off-tune "Jingle Bells" or "Mary Had A Little Lamb", albeit still squeaking loudly or playing very breathy notes. Magically speaking, that would produce an incredibly dim light, or a faintly noticeable breeze. Most people never progress beyond that, simply because you need a lot of practice to do anything more. It will be tiring, the equivalent of developing calluses when playing guitar, or an embouchure playing trumpet, but they'll still have to play every day.

Just like learning all the notes on an instrument, it's possible to learn the basic fundamentals of magic on your own, but it'll be trial and error - going a "little flat" may turn your gentle breeze into an annoying static cling problem, or perhaps your shoes will start smoldering. And using the wrong techniques may sound ok, but it'll take a lot more effort, or prevent progress by exercising the wrong muscles.

Jingle Bells is fun once or twice, but doesn't sound nearly as good as Carol of the Bells, and hitting all those high notes requires constant practice to exercise the right muscles, not to mention the stamina to be able to play for several minutes straight, as opposed to a few seconds. Magic is no different; the "high notes" produce the most effect, and the ability to cast powerful spells takes stamina and a high degree of control - it's easy to take that quiet drawn-out note of "Translate Language" and turn it into a loud squeak of "Induce Personal Blindness."

Timing, stamina, and control take a lot of practice to achieve. As awesome as it is to play a musical instrument, most people can't be bothered; likewise, most people don't want to take the time to learn how to use magic, because it takes so long before you can so much as summon fire, let alone rain down fireballs on your enemies.

Finally, magic may require some sort of focus. Powerful mages may be able to use any focus (wand, staff, crystal ball, etc.), but most mages will pick one and stick with it. Learning a single focus limits what you can do, just like picking piano over flute. And a focus could be quite expensive - that wand isn't just a stick with a handle, it's an expensive investment.

In short: learning magic is difficult even with a teacher, and the tools required to practice may be hard to find and harder to build, and limit the type of magic you can practice.

In the situation you describe, I would try looking at the real-world occult systems instead of fictional magic, since they most often try to explain, why anybody has a potential to do magic, but only a small number of their adherents can be successful. Folk tales are also a good source.

Magic is taught

I will mention it only for the sake of completeness - you've already stated that people can discover magic by themselves. There basic idea here is that magic is either very complicated ritually, or magical thinking is so significantly different from everyday thinking that you need to be taught to use it.

Magic is done by spirits

It is pretty popular too, and it may be not the best for your setting. In this version, a source of magic is not exactly in the person, but in his ability to call upon spiritual entities and coerce them. Maybe there is a shaman-style spiritual quest, whereby the prospective magic users discovers his spirit helper and then it teaches him further. It may be a matter of knowing the Names of the spirits (Kabbalah style), and knowing at least one name puts you into position to discover more.

Magic is gifted

This version also presumes the existence of the spiritual entity . There simplest example is the folktale idea of the 'deal with the Devil', 'deal at the crossroads' etc. Magical ability is conferred by a spirit as a part of some bargain. It doesn't need to be a devil, it may be an ancestor spirit looking for vengeance.

Magic is insane

That is my favorite. It is used in fiction too, but mostly in the 'magical realism' style of writing, not in the mainstream fantasy. In this version, magic exists in the world, but it's illogical and irrational enough so that an average person is just not able to think this way. Something similar to the theories of quantum physics, for example. 'The world is not what it seems' - the human understanding of events and things is locked into linear time, the illusion of actions and consequences, or the illusion of free will and similar stuff. A practitioner needs to pierce this veil of illusion in order to grasp the real laws according to which the world operates. It is a bit like Zen Buddhism this way. Such enlightenment may be a result of a long study under another practitioner, but may also just happen on its own - either as a result of meditation, or a particularly traumatic event. In such version, all magical practitioners would seem slightly mad and unhinged to the ordinary people.

Magic is like math. In theory everyone can learn math and become a professor, but to do so requires a certain amount of intelligence and without any people to help you learn and develop your math skills its going to be very hard to become any good at it.

Math in this sense is the perfect comparison. In the old ages there were mathematicians and most had their own techniques and theories to solve certain mathematical problems, there were even contests with prize money given in some places to solve a particular problem or learn a particular way of solving a mathematical problem. Now replace "math" with "magic" and you've got a perfect explanation.

1. The ability to perform magic is genetic in origin, and so is inherited from your parents.


2. The gene(s) is/are recessive.


3. An active ability to perform magic results in sterility.

This has a number of important effects. Firstly, high levels of magic affinity in a population are self-limiting. If you build up a large stock of magical genes, you're going to end up with a lot of powerful descendants in the near future but the long term future of your family line is at risk.

There are no magical families. You might be a magician, and maybe all of your siblings have magical skills too, but your parents can't have had any, and you won't have any children of your own.

The people of the "mystical race" do have a larger number of carriers of the magical genes, but have a basic grasp of genetics and understand that you must be very careful in your choice of marriage (or however breeding partnerships are formed in their culture). If your sibling is a wizard and you are not, then for the sake of your family you must be very careful in choosing a partner who is from a family with no history of magic if you want to have children who can themselves continue the family line. Alternatively, as a member of a magical family who can have children, if you wished to have magical children it is much more likely that you would be able to.

If your family has no history of magic (and therefore probably doesn't carry the magical genes) and you wish to preseve this trait, you must be careful to ensure that some of your children are strategically partnered with other non-magical families to ensure that the magic-free traits are continued into the future.

I don't recall reading any stories where the equivalent of a muggle is considered to be a special and valuable thing, whose unique abilities must be carefully preserved for the good of the future, so it would make for an unusual dynamic.

You don't play with fire

You can cast spells and everyone knows this, but doing so may kill you. Like Fred. He was stupid and one night he got drunk, decided to cast a spell, and blew himself up and half the block with him. People have come to believe that magic cannot be controlled. In fact, it might very well be a curse. Magic is strictly forbidden as a result and people who openly cast spells are considered to be reckless or terrorists.

That having been said, there's Waghort's (any resemblance to Parry Hotter is purely coincidental), which teaches people (in secret) that magic can be controlled, and they have several powerful mages who do so, like their leader Dombledure.

My first thought is to specify that the magical training people must do is physically/emotionally/mentally torturous somehow. They must undergo this training to have any magical ability at all, and it is the torturous conditions itself that causes the magic to manifest initially. You could also throw in that one of the races is predispositioned to handle the torture (without dying/losing their mind/becoming recluses) required to use magic.

This would mean that:

• Most probably won't stumble accidentally on their magical ability b/c they avoid torturous conditions


• The people that do know how it works won't want to do it unless they are sufficiently desperate


• The person will have to be very dedicated and strong-willed to get through said "training"

Then, the reason your changeling could do magic could be to do intense childhood trauma. Child slave, abandonment, emotionally terrifying moments, the possibilities are endless for an abandoned child in a rough urban setting. Through these trauma, he suffers enough that at some point he inadvertently realizes he can use magic, and begins to understand how to control it (obviously with some hilarious, destructive, or serious consequences). This could provide a cool, mysterious backstory , as well as a motive for why a ship would pick up a random changeling.

Magic is dependent upon a limited resource.

Niven's The Magic Goes Away series considers a world where the power behind magic mana is a limited resource, one that is depleted by usage.

If hoarding mana, etc. is needed to perform magic, magic will be rare. In Niven's series, mana was formerly abundant and magic was common and extravagant, but it became rarer over time as the mana was depleted.

You mention blood-magic. In Niven's world, this is potent because it relies upon the natural mana concentrating effect life-force has.

Stronger Mages use up all the available mana

Mana comes from the natural world, however like water in a lake, if it's drained faster than it fills it soon becomes empty. Years of practice allow Mages to pull most (or at least more) of the available mana as soon as it permeates their area. Most people never get good enough to snag more than a thimbleful of magic, especially if they live near to a well practiced mage.

This also explains why most mages' towers are far apart (so they can get more mana without having to fight for it) and why mages in cities/towns generally hate each other (since they're constantly battling to draw 'their share' of the available mana.)

Even further, this explains why you see so few fantastic creatures in or near cities, as their very existence is predicated on an environment filled with mana. When they attack cities and towns, it's not because they're particularly angry at the townsfolk, but because they've divined that something in the city is the source of the painful "mana-dryness" they're suffering from. Most (especially non-sentient creatures) aren't smart enough to realize that the wizards are the cause and so their attacks are more like a wild animal lashing out at something it doesn't understand.

The ability to do magic is relatively common, kicking in gradually in your 20s or 30s. (Growth hormones suppress magic.)

(Going off on a tangent, you could have sex hormones also suppress magic. Thus the most powerful mages are post-menopausal women.)

However, magic is dangerous. Unless you have had a lot of training, you are more likely to blow up your neighborhood than to light your candle from your chair.

By the time they are old enough for magic power to manifest, most people are wise enough to not want to take the risks.

"Hold my beer while I set off this fireball" just isn't as appealing once you've survived to your 30s.

Take @ZeissIkon's and @StarfishPrime's answer (recessive genes) and add a cultural limitation.

This will make a rare gene combination even rarer.

What if the powers that be feel threatened by those who can do magic?

They may actively stamp out anyone who shows signs of magic, maybe even going after their families as well; killing or social stigma. In the first case, a number recessive carriers are directly pulled out of the gene pool. In the second case, the remaining members oft he family have a lower chance of breeding: "look, it's a Jones, they had a cousin a couple of generations ago who produced a mage, better stay away from them."

Or, they allow magic but only as part of a power structure that limits breeding. Magic is only allowed for priests and nuns (who aren't allowed to breed). Combine this with shunning and the gene pool gets filtered over time.

This doesn't even have to be the current power structure. If such a structure was in place for a long enough time in the past, even if it is largely forgotten, the result would be what you are looking for.

What if those in power ARE the ones who can do magic?

they got in power because they can use magic. It gives them an advantage and is something that they can point to as proof that they have some divine mandate to rule. They don't want to risk losing their advantage.

They would have the incentive to pass laws or just use their strength to nip any non-noble who can cast in the bud as soon as they are detected. The stupid ones would wipe out the families of anyone who shows signs of magic use. The smart ones will recruit the "common" mages as front line troops (get use out of them and whittle down their numbers).

Again, this doesn't have to be a current civilization. A past civilization will do just fine.