I am realizing this is difficult to express concisely.

Let's for the sake of this conversation narrow down our definition of intelligence as "the ability to acquire and apply knowledge and skills" which also presupposes some form of ability to maintain intense lengths of focus and concentration required to learn these skills and acquire said knowledge.

I will preface by saying surely there have been people whom society would have viewed as "not having the right genes" accomplished many great feats and tasks. And surely there have been geniuses, or what we view in a certain lens as "genius" without having had a reputation for being particularly intelligent.

But the point I am making has three parts:

Point one: If you take the purely metaphysical approach, there is a maximum capacity for intelligence that any one individual has. Evolutionary biology has told us, thus far to our understanding, that this is brain size. Going down this same road, that means certain people have evolved, or fitted more advantageously for intelligence, and some for other things like strength, others for other traits that are important, so on and so forth (by the way to go ahead and nip in the bud, this isn't saying one is better or more important, so don't take this as any kind of statement of supremacy). Genetics plays in part your maximum capacity, for some function of intelligence: whether its the sheer number of skills and knowledge you can acquire, I haven't done enough research personally to make an accurate statement there, but I do know that we have limitations and those limitations are determined by genetics.

Point two: You can certainly overcome some limitations. But your effort to overcome efforts and become "genius" at a given field is still hampered versus someone who puts in the same effort and has the genetic platform. That is why you still have the "scrappy" players in the NFL that are clearly inferior genetically but have carved out a niche for themselves, or you have business people that have a "stroke of brilliance" But in order to obtain maximum human potential for intelligence, the genetic platform first needs to be there, and then you need to put in the consistent effort to acquire the skills, to put them to use.

Said another way someone genetically inclined to gather knowledge is going to accomplish more knowledge gathering than someone not genetically inclined to do so. Just as my lanky and bony arms are never going to lift as much weight as someone who has tree trunks for arms if we hit the gym the same amount of times.

Point three: Yes there are scrawny and scrappy, the "brainless" that have strokes of genius, the people who overcome improbable disadvantages to achieve greatness. But we are talking about the most likely scenario. I have 3 brothers and my oldest was always considered the most intelligent. We had the exact same upbringing and exposure to resources and tools. Our genetic expressions determine our propensities to engage in certain behaviors, which lead to certain interests, which lead us down different roads. Our environments help carry us along those paths.

The ones that are truly great, or "genius" or "best of all time" in a sport, have gone down a road they have the genetic propensity for, and utilized their capacity to its fullest, through consistent effort and energy.

This is at least my current model of the world through my life experiences. Do you think it is grossly incorrect? Happy to be corrected, or incorporate more factors.