(Also H/T Ken.)
For the peanut gallery, what this means is how much math you’ve learned in life is almost as heritable as how intelligent you are. In other words, people who fall behind where their parents were in math almost always catch up somehow because the drive to do so is genetic, and people who get ahead of where their parents were in math fizzle out.
It’s not a perfect correlation. IQ is about 75% heritable and I still have a standard deviation on the average of my parents, which is unusual but not unheard of. But basically, if your parents took Calc 1 and then stopped it’s likely you will have the same math achievement level even if you’re separated from them at birth. As you’d expect, both of my parents took calc 4 (differential equations) and then stopped. I went very slightly further and then stopped. My siblings mostly stopped between calc 1 and calc 4.
Kid 1 – calc 2
Me – Partial differential equations (basically calc 5)
Kid 3 – precalc
Kid 4 – calc 2 (I think)
Kid 5 – calc 1 (I think)
Kid 6 – calc 4
Blacks are 13% of the population and most of them can’t perform 4th grade arithmetic as a consequence of verbal tilt on an 85 average IQ. And apparently, it’s so strongly genetic that it literally can’t be fixed.
Something else that occurred to me regarding Kid 3’s particularly low math achievement, despite his IQ (~125), is that another big difference comes from the split in the Openness dimension of the Big 5 personality model. On the one hand you have Aesthetic Interest, which is often much higher among women with high Openness. On the other hand you have Intellectual Interest, which is often much higher among men with high Openness. Kid 3 was, as a young adult, much higher in Aesthetic and basically uninterested in Intellect until his late twenties. I was the reverse, only recently (early thirties) having become interested in anything aesthetic or even the concept of “decorating”. And truthfully, it’s only because I’ve realized that aestheticism (and leading a balanced life in general) makes me better at intellectualizing, so in a roundabout way I’m still Intellect-maxing.
A good heuristic for this is autism quotient. It’s not perfect, but it’s pretty good.