Inheriting the magical blood down the line, via a wizard father or a witch mother is understandable in case of Half-Bloods.

I am wondering as to how Muggle-borns end up with magical ability?

  • 42
    I'm guessing magic. ;) Commented May 5, 2011 at 12:52
  • 2
    @Bill: Beat me to it.
    – Jeff
    Commented May 5, 2011 at 16:08
  • Beat me to it as well, as soon as I saw the question I knew the answer. Commented May 5, 2011 at 17:19
  • 26
    Canonical answer is "Higher concentation of midi-chlorians in blood". Commented May 5, 2011 at 18:11
  • @Sunny Boy: What's the reason for the bounty? You already have a very good response, including a direct quote from the series author on the subject.
    – Jeff
    Commented May 13, 2011 at 17:51

11 Answers 11


The best theory I can suggest is that magical ability is like a recessive gene. If each Muggle parent is a carrier, they can produce a magical child. (However, this theory only works if you exclude Squibs :P)

Also, quoting JK Rowling:

"Muggle-borns will have a witch or wizard somewhere on their family tree, in some cases many, many generations back. The gene resurfaces in some unexpected places."

  • 16
    Assuming we're all one species, the fact that wizards have achieved the level of separation of magic kind from muggles that they have is remarkable, while still retaining inter-breeding capabilities.
    – Sam
    Commented May 5, 2011 at 14:26
  • 4
    @Sam: Not remarkable, merely magic.
    – Jeff
    Commented May 5, 2011 at 16:07
  • 4
    @ykombinator You can account for Squibs if you add a gene or two, and make magical ability require the appearance of both dominant genes. For example, if an AaBb wizard marries another AaBb sorceress, they could potentially have an aabb child, i.e. one with no magical ability whatsoever -- a Squib. A match between an Aabb Muggle and another aaBb Muggle would still be able to produce an AaBb wizard.
    – Uticensis
    Commented May 9, 2011 at 3:31
  • 2
    @Billare: The occurrence of squibs seems to be small enough that I doubt it could be that simple, but it's a good simplification of what is certain to be a complex set of genes that need to work together.
    – Jeff
    Commented May 13, 2011 at 17:38
  • 5
    @Billare: Squibs seem to have at least some tiny amount of magical ability, though - they can see magical creatures, whereas muggles can't. Some of them, it's implied, can do very minor magic, at least to the point of a spell going off improperly. If a Squib were indistinguishable from a Muggle, you may have been correct in it being a single gene, but given the differences I don't think a single gene can explain everything.
    – Jeff
    Commented May 13, 2011 at 19:50

A study in the British Medical Journal concluded that while there is a genetic basis for magical ability it involved the interaction of several genes, some recessive. This explains why muggles can produce magical offspring.

The study addressed not just general magical ability but specific skills such as the ability to speak to snakes.

The study is here: http://www.bmj.com/content/335/7633/1305.full.pdf

  • Death delusion?
    – flq
    Commented Apr 7, 2013 at 19:37

As ykombinator wrote, JK Rowling has spoken on this issue herself.

I believe it is likely that there's a series of genes tied to having magical ability (plus some magic, I'm sure, since there simply CAN'T be a purely biological explanation).

It's probable that there are a series of genes that are linked together, and that many Muggles have 'damaged' versions of these genes - this could account for the various mediums, psychics, etc that exist in the Muggle world (those who aren't faking it, at least). If this is the case, a single random mutation in the gene could fix it for two muggle parents, or two muggles could have a child who gets healthy versions of the gene from one or more parents (the genes do seem to be dominant, since Muggle + Wizard invariably ends up with a Squib or a witch/wizard).

Some of the genes likely control the ability to see magical creatures (these must be fairly robust, since Squibs can see Dementors), some to the ability to control magic, etc. Squibs most likely come in various degrees of magical ability (or non-ability) as there's at least the perception that they can learn magic - otherwise the market for Squib magic teaching supplies would dry up quickly.

  • 1
    Saying there can't be a purely biological explanation of this distribution is an very strong thing to say, and I seriously disagree with that opinion. I still don't understand why a two-locus model wouldn't work to explain Squibs and Muggles. You can account for "half-abilities", like you say Squibs have, by making one gene of the pair dependent on the other.
    – Uticensis
    Commented May 14, 2011 at 0:22
  • 1
    @Billare - There's more than just "half-abilities" though. Different witches/wizards have different levels of power, not just a '100%, 50%, 0%', or any of the simple combinations of 'On' and 'Off' you can get from a two-locus model. There are people who are technically squibs who can use minor magic successfully (akin to an illiterate who can spell their name). Also, there are still major differences between squibs and muggles, whereas your 'two-locus' model leaves them genetically identical, as far as magic is concerned.
    – Jeff
    Commented May 16, 2011 at 13:39
  • 2
    That squibs can see dementors is never actually established; in fact Mrs. Figg's description of the event, while accurate in describing the effects, seems to Harry to have come from books as far as describing the dementors themselves, and Madam Bones seems rather taken aback by the assertion, having it noted for future investigation. Whether Arabella Figg actually saw the dementors, or just imagined she saw them, knowing what must have been causing the scene she did see before her, is a question that is never answered. Commented Jul 11, 2014 at 11:14

It could be:

  • a random alignment of junk DNA that winds up coding for magic sensitivity, as was stated before

  • that magic chooses and unborn/young child somehow linking with them

  • proximity to magic in use in utero or in early childhood

  • random chance (such as the existence of squibs in major wizard families)

Take your pick, I pulled the last three out of a hat. They all are based on random chance, and a small one at that.


Muggle-borns get magic from wizard ancestry.

In his notes on “Babbitty Rabbitty and her Cackling Stump” in “The Tales of Beedle the Bard”, Dumbledore mentions that the Department of Mysteries has studied how wizards get magic, and has found that wizards born to Muggles have a wizard somewhere in their family tree, possibly generations apart.

“As intensive studies in the Department of Mysteries demonstrated as far back as 1672, wizards and witches are born, not created. While the “rogue” ability to perform magic sometimes appears in those of apparent non-magical descent (though several later studies have suggested that there will have been a witch or wizard somewhere on the family tree), Muggles cannot perform magic. The best — or worst — they could hope for are random and uncontrollable effects generated by a genuine magical wand, which, as an instrument through which magic is supposed to be channeled, sometimes holds residual power, which it may discharge at odd moments — see also the notes on wandlore for “The Tale of the Three Brothers.”
- The Tales of Beedle the Bard

Therefore, Muggle-borns still get magic by inheriting the trait from someone in their bloodline, though in their case it’s from a more distant relative than their parents.

  • Then how did the first wizard get magic?
    – Alex
    Commented Aug 25, 2019 at 1:08

Magical talent, if it is indeed genetic, would be linked to a wide number of genes. Many of the most famous witches and wizards in the Harry Potter series are folk heroes who are well known as half human. Halfbloods not of wizarding blood and civilians, but of normal humans and some variety of magical creature. Merlin himself was a demigod, son of the celtic goddess of magic and one of her last mortal worshipers, a woman with no talent for the art. Cercie, babayaga, Morgan LeFay and many others, hell they even included angreboda, the mother goddess of the frost giants durring the 4th book.

Add to that the interview with JKR herself who said that there's really no such thing as muggleborns, but rather the multigenerational decendants of squibs the answer seems clear to me. You want magic ability you have to have some sort of magical ancestry.


Most of these types of questions assume that magical people have some special bit of DNA that turns them magical. In other words:

  • human without special bit of DNA = muggle
  • human with special bit of DNA = witch or wizard

However, that only works when you look at humanity in isolation. When we take a look at the whole HP universe, we have to take into account that non-magical species outnumber magical species. Why? Additionally, we have to take into account that magical humans are only a small percentage of the human species, which doesn't make sense if magic was in any way beneficial, because evolution would have selected against non-magical variations in that case.

The only logical conclusion therefore is that magic isn't a beneficial ability. Which makes sense when you start looking at possible diseases. When you're magical, your body has to be able to defend itself against both magical and non-magical diseases. However, when you're non-magical, your body only has to defend itself against non-magical diseases.

In a way, the ability to perform magic is like colour-blindness. It's a disadvantage for the individual, but it can be beneficial to the population as a whole as long as it occurs only in a small percentage of the population.

So it should be the other way around:

  • human without special bit of DNA that protects them against magical diseases = witch or wizard
  • human with special bit of DNA that protects them against magical diseases = muggle
  • 3
    How can colour-blindnes be beneficial to the population as a whole?
    – vsz
    Commented Aug 2, 2013 at 8:48

As a magician and muggle, I think magic happens out of intention. Most of the great masters of the art talk about the need to believe and intend the magic to happen and it will. I believe this is true in both fantasy and reality.


One of the lessons of the book, illustrated by Hermionie, is that people rely too heavily on blood and genes to define their talents. People labeled as Squibs are still capable of basic magic it just doesn't come as easily to them.

I would wager that anyone is capable of becoming a wizard if given the time, discipline, tools and knowledge. Just like people are not just born with a given talent for math, people pick up traits through their life and growth. One who grows up in a wizard family will likely pick up wizarding skills, just like someone growing up in a house of mathmaticians probably picks up math pretty easily.

Nature vs. Nurture.


I believe that squibs are the reason for muggle-borns. Centuries ago, I would imagine that squibs would have been cast out of wizarding society. Those squibs would have mingled with the muggle population. Say, generations down the line, two different squibs decendents marry and have a child. That child would have a greater chance to produce magic because his/her genetical makeup still has the magical gene, though stronger than either of his/her's parents. I do wonder however if the child of a regular muggle and the decendent of a squib would be magical.

  • 2
    Hello and welcome to Scifi.SE! Interesting theory, but pure speculation, which we don't encourage on this site. Maybe you can add a few pointers to the details that make you believe this?
    – Kalissar
    Commented Sep 16, 2013 at 7:27

Another explanation, based on a real-world phenomenon called "trinucleotide repeat expansion": some genes comprise a number of repeating, three-nucleotide sequences (such as CAGCAGCAGCAG...) When such repetitive DNA string is copied, mistakes often happen and the number N of the "CAG"s will change between the generations. Usually N increases but a reduction is also possible, though rare. If N is less than a given value, say 25, the carrier is not affected (normal phenotype). If N is greater than, say, 100, the carrier will be affected (sick). In between, you may be affected or at least your children have a higher risk to be. So, let us assume that N is linked not with a pathology, but with magic.

So, for example: N less than 25 - Vernon Dursley;

N between 26-50 - a Muggle, low chances of having a magical child;

N between 50-100 - a Muggle, children may be magical or not (parents of Lily and Petunia);

N between 100-150: you may be able to perform some forms of magic, children in all probability magical; Squibs having some magic would be there;

N between 150-200: a wizard/witch;

N between 200-250: a powerful wizard/witch; N between 250-300: Grindelwald, Dumbledore, Merlin etc.

A few assumptions more: N more than 300: lethal, DNA becoming unstable, the embryo does not develop; thus the power has limits. This would explain why Mr Weasley said "without marrying Muggles, we would have died out". Squibs would be victims or rare deletions (N drops). As deletions are rare, Squibs would be less common than Muggleborns which seems to be the case. This model also explains why Muggleborns often have Squib ancestors: after the deletion, N starts re-growing, starting from a non-magical but relatively high value.

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