You either have it or you don't. You can learn knowledge and education, but most intelligence is instinctual, and much of that is genetic. I don't think intelligence really comes from environment, because it's not really ever "learned," but I don't think it's completely genetic, either. But what do I mean by "intelligence?"
The easiest way to determine common logical intelligence is to see how easily someone can understand something, break it down, and explain it in simple terms. Intelligence also usually comes with open-mindedness and knowing that the more you learn, the less you know, so some humility, as well. That's why pseudo-intellectuals are often know-it-alls (like many 2010-era atheists), or people who often speak in extremes like "all people this" or "x-people never..." and so on. Finally, I think self-awareness is a big sign of intelligence, as dumb people tend to lack it, and intelligent people tend to hide their self-awareness (because it can be depressing, at times).
Intelligent people (in my opinion):
1. Can understand complex things easier.
2. Are open-minded.
3. Are humble about the universe and their role in it.
4. Have self-awareness.
I consider myself extremely intelligent with most things, and can tell you my mother (abusive and all) is VERY unintelligent. My Afro-Cuban father seemed to think he was Scarface, even though I never knew him well, so I didn't get it from him, either. I'm not sure where it came from, because it didn't come from my sh*tty-ass ghetto environment, either. But out of every external source, my 'mother' is perhaps the least intelligent. If we were to use IQ numbers to quantify it (I don't take IQ too seriously, but I like the quantifiers of it), I'd guess her IQ is in the late 80s, early 90s. She's pretty f*cking stupid. And stubborn too, which is a deadly combination.
Speaking of stubbornness, that's something I *did* inherit. But I am stubborn about social things (like, I won't date "bisexuals" for example). I acknowledge my stubbornness with these things though, because my emotional side can't handle some extremes like that. I'm not looking to date queer women or participate in orgies anytime soon, but I don't think it makes me closed-minded.
I think you can understand complex things, be open-minded, admit you don't have all the answers, and have self-awareness, but don't have to possess all four of these things at all times, and with everything. After all, we are just humans and not machines or aliens... Unless you own Facebook.
But I think less than 5% of the human population are intelligent. Not "educated" like doctors and lawyers, but truly intelligent. Like "at least a 140 IQ" if we want to go by that. (I'm 150, and I feel dumb as hell; I only can say I'm intelligent because most people I've ever met seem to make dumber, less rational decisions than I do more frequently and will think things through far less.)
So if like 1-4% of the population is intelligent, 21-24% of the population have "minimum acceptable intelligence" (aka, "average" smarts), and let's just say 75% of the rest are just morons, what does that leave us? Well, politicians, of course! Even Napoleon knew that! Yes, the world isn't run by, nor generally respects, the highly intelligent, even if they're the ones saving everyone's asses at NASAs SETI program, or curing diseases with vaccines like COVID-19. Instead, the world seems to look up to the Trumps, Bidens, and AOC's of society, along with Hollywood weirdos and roided-up athletes who play with balls in and out of the locker room. In other words, ignorance is bliss for a reason. Be glad you're not super intelligent. You'd possibly just be cynical, all the time!