I wouldn’t go that far…the “no superhuman powers” clause would be sufficient to weed out the demigods, in my view.
I’d vote for Kaylee before River.
Achren - No reason we can’t have both, as long as we include Mal in there somewhere. And we should throw in Zoe and Wash, while we’re at it. And Inara would be okay, too. Unfortunately, Book’s too old, Simon’s River’s brother, and Jayne’s, well…Jayne. No reason to bring him along.
StG
Perhaps we need an addition guideline:
Must work well in groups or with partners.
Holmes’ habit of withholding essential information could get somebody killed.
We need a Tribe, not a conglomeration of loners.
Are we looking at too old a set of women? Let’s face it, the prime consideration for the women is going to be the length of time they can breed. All else is minor. Most of those considered so far are 25+ - that’s 10+ years after menarche and thus wasted breeding time. So we need to look at healthy females not long post menarche - enough time for their bodies to have settled down anyway 
- 14 or so. Or those with extended fertility (qv Arwen and most Numenoreans). Given the age range of, say 14-16, which fictional women would you include?
In some primitive societies, women weren’t permitted to marry until they had proven their fertility. Very few fictional women aged 14 to 16 have done this. I woud suggest that the age range be bumped up to 18 to 21 with the caveat that those chosen have already reproduced. I will always lust after Emma Peel, but she was well into her 20s, married with no offspring. Shouldn’t this disqualify her? The only women on these lists that have had children are Sarah Connor and Hazel Long.
I would sugegest Odysseus" wife Penelope. She ran Ithaca while Odysseus was out wandering around. She had a child and managed to avoid marriage to important suitors while waiting for her man to come home.
Using fertility as a criterion, then Xena and Gabrielle would be good choices also.
How come nobody else picked up on Kimball Kinnison when Jonathan Chance threw out the name? He and Clarissa MacDougal are tough and smart, and they’re proven breeders!
Lazarus Long is a shoe-in, and if the rules allow Minerva, she is, too.
Indiana Jones and Lara Croft may not be as much team players as the others, but they’d be good picks.
I have to agree on MacGuyver.
How about the narrator from The Swiss Family Robinson? The dad. I can’t recall his name, but the dude could build a civilization out of anything.
Look, if there’s only 12 humans on Earth and they’re all in the same colony, there will be nothing to fight but animals. And for near future, dangerous animals will remain easy to avoid, and, in any case, relatively easy to beat, even by humans armed only with spears and arrows. (That’s how our ancestors triumphed.)
Is Friday Jones too “superpowered” to qualify? If not, she’d be ideal – provided she can get her sterility reversed. (It is reversible, but only by a specialist with access to the very best lab facilities.)
I’d nominate Gwendolyn Ingolffson from Drakon, but she’s way more superpowered than Friday, and as a Homo drakensis she can’t breed with Homo sapiens although she is of human-derived stock (with some jungle cat, etc., added to the mix). No surgery will help there, she has a different number of chromosomes – that was designed into the drakensis to prevent crossbreeding with sapiens or servus.
See discussion posts 82, 85, 88-98 inclusive. 
12? Don’t need no steekin’ 12.
Ayla plus Jack Bauer.
But if you insist on adding more, would Mendoza of Kage Baker’s Company novels qualify? She’s a human cyborg.
Middle-Earth != Earth.
No clear consensus reached.
That doesn’t mean that it was easy for them. Twelve people against a runaway tiger? Or a bear? I’d like to have some people who can fight on my side, thank you very much.
Sure, our ancestors triumphed, but it was probably a war of attrition, at least at first. That’s why I voted for Shanna O’Hara, aka Shanna the She-Devil.
She’s also complete scum, from what I’ve heard, and not really very human, what with under the skin armor and such. She’d promptly enslave everyone else, or try. Also, looking back :
Wouldn’t work. According to Benda herself, the Saurons were qucik-and-dirty supermen, with little consideration for long-term genetic problems. She can interbreed with normals just fine, but is a mass of exotic nasty recessive genes. With a world’s worth of people, that doesn’t matter, as she pointed out in the story; with just twelve, she’d probably doom the generation or two after next when the recessives started doubling up.
If you’re looking for young women, how about:
Podkayne Fries: high IQ and strong maternal tendencies
Nancy Drew: smart and resourceful.
Any of the girls from “The Waltons” – farm background, likely high fertility
Is that a question or an exclamation?
If a question, then yes Middle-Earth does equal Earth. If you want details, start a thread and the Tolkien Fans on the boards will provide extreme detail and cites. Plus we’ll through in genealogies and humor in Quenya.
Jim
A declaration. By the terms of the OP, neither Boromir nor Aragorn nor Eowyn would qualify, fuggedabout Arwen.
I don’t understand your point. Middle-Earth is a pre-historical period of Earth.
Arwen can reproduce with normal humans. The Op specifically mentioned that Arwen would qualify. I don’t think she is a particularly great choice, but she does qualify.
The OP contradicts itself. If I squint I can just maybe buy Conan’s Hyborian Age as a “prehistoric Earth.” But not Middle-Earth. That world has as much in common with our world as the Mercury of Eddison’s The Worm Ouroboros.