> Where's the data backing up what you said?

What he is saying is the default hypothesis based on our understanding of biology and psychology. If you have variability in genes you'll get variability in characteristics that are connected to them - height, bone structure, mental capacity, etc.

It is on you to prove that there is an arbitrary cut-off when it comes to this variance from which point it doesn't matter in regards to e.g. cognitive and mathematical ability.

> Enough that they could recognize whether a mathematical concept is applied correctly (e.g. if I have a 2% monthly interest, should I multiply it by 12 to get the annual interest? Why, or why not?) and conversely to correctly apply concepts they already understand to new situations, as well as to leverage those concepts to potentially learn new ones that depend on them.

No it doesn't if they do not have the abilities to comprehend it. I think you're living in a bubble of at least average-smart people and don't get that probably millions if not billions of people around the globe (based on average IQs) won't really get that concept.

>If you have variability in genes you'll get variability in characteristics that are connected to them - height, bone structure, mental capacity, etc.

Then you're agreeing with me. The thing all of those have in common is that they follow normal distributions. The shortest recorded adult and the tallest recorded adult are quite far apart, yet the vast majority of adults are between 150-200 cm tall. That's precisely what I was saying; the outliers of mathematical skill are very very far apart, but most people are roughly equally capable.

>I think you're living in a bubble of at least average-smart people and don't get that probably millions if not billions of people around the globe (based on average IQs) won't really get that concept.

What I'm saying it that it even someone with below-average IQ could do it, if taught properly. Mathematics is less about being smart and more about being rigorous.