As we learn more about the brain? Sure. Possible. Any evidence so far? No.
This statement is exactly what I consider fallacious. There is plenty of 'evidence' for BOTH cases(intelligence variation vs. no variation) but nothing CONCLUSIVE. Those are not equivalent statements. And the scientific classification of species and subspecies are very nebulous. Under current reasoning a chihuahua is more closely related to a husky than the husky is to a wolf. Because of behavioral differences. Yet those behavioral differences diminish greatly even after only a couple of generations of domestication. It's not so cut and dry.
Judging purely on phenotype, I can only imagine that an alien would classify myself, a person of Asian descent and a person of African descent as different subspecies. The behavioral differences across those cultures is significant as well. Of course, it may not even be a matter of genetics in the fictional game world. Lower income, lower living standard correlate with lower intelligence(so far as we can measure). The relationship is not causally one-directional. Being raised in the ghetto will diminish your output relative to direct family members raised in different environments. The cause of ANY of this isn't really that clear. But I just don't think it's unreasonable to assume minor differences among such obviously different phenotypes. Of course, in the end...we all know it's primarily about game balance and interesting and different player choices.
Well, a lot of things we talk about are subjective... even the tests we run are subjective

For a long time, IQ tests were thought of to be the best way to determine intelligence.... and a rating system was developed (you know, so those assholes out there can go "I have an IQ of 121! listen to me now!") but then some people disagreed... and test were done, and done, and done again. until you get to now, where people finally admit that IQ tests
MAY not be the best way to determine intelligence (BUT IT STILL COULD BE!!!!!!!).
As you point out too, a lot of what we accept as "evidence" comes from our social background. If your social back ground comes from a teaching that says "Yours elders are the wisest", you would question anything said that went against the word of your elders.... regardless of who said it. And, depending on your social model, morals, ethnic views, education, and world view, you may believe that communication between people outside of your "zone" to be impossible. And you could be right.
But we still try

And for the most part we get through to each other..... but not until we figure out exactly what the other person means as "Evidence". From there we try to frame our conversation to get our points and views across. And from there, we get 21 pages of topic...... with 18 of them being "SCREW YOU!"-"NO SCREW YOU" posts
I have found these rules to be helpful on the internets and in dealing with people on the internets.... (But, yes, you may have found others, or different ones. But yours don't matter. My evidence says so!

)
1:
THICK SKIN REQUIRED Currently something like 4.5 BILLION people are online. Considering that I can't go shopping without me running into some asshat I desperately hate, the chances are good I will run into a lot of those in the web. For whatever reason, those same people seem to like saying and doing to most inappropriate things. (I am guessing that they get beat up a lot). Add to that, the "invisibility" of the web, and people think they can do whatever they want! Deal with it, or get off. The web ain't going to change.
2:
English don't mean EnglishJust cause the text on the screen is in English, doesn't mean that the other people "talking" on the web speak it, or think it. And just cause you think "English" don't mean understand "English" either. A Fag. A torch, A rubber. A loaf. These are mean different things to different people. Don't assume you know an insult from a complement, you just may be surprised at what your "online buddy-buddy" actually called you

3:
Watch the world burnNo matter what you say, no matter what you do, there always seems to be that retard on a forum banging head into the wall while screaming "The sky is red, the sky is red!!" This is what the ignore button is for. Learn it. Use it. Love it. Honest it take the stress out of the day, and keep you from going "There went 10 minutes of my life i'll never get back" after reading this moron's new pabblem post about what nerf/OP/cheat/whine is his newest issue. And you can bad mouth them, and not worry about their response! (it's kinda fun!)
4:
Laugh at everything!No matter the topic, laugh at it. Good humor can carry you a long way in a debate. Just don't share it. No one likes to hear someone go "LOLOLOLOLOLOLOL YOU'RE A MORON!!!! LOLOLOLOLOLOL!!" I know you're doing it (cause I do it ALL THE TIME HERE!!!)

Just keep it out of your posts as much as you can. And if you can't, might I suggest Rules 3 or 1 for you to try out?
*******
Folks, we all take what is said here far too seriously

Sit back, relax, have a beer, ENJOY your self.