Listen, ok, LISTEN, this will sound mad all the way until the end, and I don’t promise it’s worth it but LISTEN.
We are told that 80% of the population in BNHA has a quirk. BUT only 5% of Isuku’s and Bakugou’s middle school class is quirkless (only Izuku (1) out of 20 students).
ok, you tell me so what? Hirikoshi, a managaka not a mathematician, got the math wrong, who cares?
Except we know the amount of quirkless people is going down as a factor of time when admitting to Izuku that he himself was quirkless in youth Allmight says “it wasn’t as rare as for your generation"
This makes instinctive sense right? we know at least two people that got both their parents quirks or a fusion of the two (Bakugou and Todoroki) we can even extrapolate that Uraraka must fall in this category, and we know one person that inherited their quirk from only one parent (Mirio)
ok this is the point where I admit this post is all about math, but bare with me.
for this all to work we have to make some (absolutely blatantly wrong) assumptions about bnha society (or the math will get completely out of hand)
assumption#1 every member of bnha society lives to exactly 80 (an approximation of japan’s current life expectancy) at which point they blow the candles and die.
(this assumption is false, we only meet two (non-supernaturally) old people, and we know at least three characters die way before age 80 (R.I.P))
assumption#2 bnha society has a perfect replacement rate of an average fertility of 2.1 children per woman so there is an equal amount of people of each age between 0 and 80 years old (at which point again, for the sake of simplicity they all painlessly die)
(this assumption is false, we see the family of five 1-a students and not all have one sibling and some have more than the replacement need of only one sibling)
and the final assumption is that (because this would be really hard otherwise) quirk-havers increase as a percentage of the population linearly (not exponentially as one should assume)
This is where I reveal that I suck at math, so I had some father-daugter bonding time with my very-good-at-math father to figure this out and I still don’t quite get it but this is what it looks like, COME @ ME
the end results produce these graphs
this more elegant (but not as easy to read)
and this far easier to read
on the x axis with have years in descending order from the current year of bnha
and on the y axis the increasing percentage of people having at least one quirk
ok but this is where it gets interesting, according to the math the first year that 100%of newborns had a quirk was roughly 5.3 years ago in the anime.
THIS IS PRECISELY WHAT I THOUGH WAS THE CASE, my hunch was that the math would have given this exact answer.
If 5.3 years ago was the first year of people all born with a quirk, and if quirks manifest around age 5 roughly a third of a year (or four months) ago is the first time all those kids manifested their quirks.
four months ago…. you know… when Izuku had this vision
and MANIFESTED A SECONDARY QUIRK
ok, I know this is making you all, at home have this reaction
I ALSO don’t think Hirikoshi gave me math homework on purpose!
this is the math to figure out the likelihood of someone born the same year as Allmight (who is currently assumed to be 49 and cannot be any younger than 46)
so there was a 25% change of being born quirkless that year, a full five time likelier than the 5% of Izuku and Bakugou’s year
finally as the graph shows there is point where the percentage of quirks reaches the x axis A.K.A. where the perchentage of quirk-havers begins it’s ascent, also known as the first quirk, the glowing baby in China.
that entrepreneurial baby started glowing roughly 178 years ago in the bnha world.
giving us an upper limit to the age these two avocados can be
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