"So you won't go out with me 'cause I'm a caveman? Well, the joke's on you: this 'Insta-volve' pill will shoot me right up to Homer Simpson!"
"I hope you mean 'Homo sapiens.' Anyway, evolution is supposed to require numerous generations of micromutations."
"You only say that because it rhymes. But this has the special ingredient, 'Hopeful Monster.' Watch! Nyah! Ygyde-ygyde-ygyde... D'oh!"
"Definitely a hopeless monster."
What limits does Genesis impose on our stories? Surprisingly few. In fact, it allows a potential storyline that's seldom used. I don't believe there's a gap between the first two verses of Genesis, but someone could write a story about a pre-Adamic civilization. Unlike regular lost civilization stories, there would be no real connection with our world, but it could still be an interesting idea.
But when you mention Genesis and spec-fic, the two questions that come up most often are timelines and evolution.
The timeline: Are we restricted to about 6000 years of human existence, beginning with Creation about 4000 B.C.? Well, why should we be? Does the Bible state such a limit? No, but it has genealogies that tell how long the people listed lived. If you can correlate the genealogies with known dates, you can work out roughly the date of Creation.
Or can you? The idea contains some hidden assumptions--for example, that an ancient genealogy functioned in ways immediately obvious to moderns who know nothing about the language or culture involved. Knowledge of the culture tells us that ten-person genealogies were a popular literary device in the ancient Near East, and that's what we find in Genesis. That doesn't make the genealogies fictitious, but it does mean they could be incomplete. If you compare the genealogy of Matthew 1 with the kings list in 1 Chronicles 3:10-16, you find that in Matt 1:8 Jehoram (other versions "Joram") was the father of Uzziah/Azariah; according to 1 Chron 3:11-12, it was Jehoram, Ahaziah, Joash, Amaziah, Azariah: three generations are omitted, and that in a numbered list. It's not an error; Matthew just tweaked the list to make the numbers come out right. (He was a tax collector, after all.)
So if genealogies could omit several generations (and Matthew is not exceptional that way), there could be more time in early Genesis than some people think. There should be enough (speculatively speaking) for a lost civilization. But that will make some people uncomfortable, because it might open the door for some degree of evolution.
So what about evolution? Well, Adam didn't evolve: he was an inorganic sculpture one moment and a living, breathing man the next. (No, he wasn't a hominid suddenly "ensouled," to use an unbiblical, Western nonsense term. The wording doesn't allow it.) And it's effectively impossible to harmonize evolution with Genesis 1, which I consider historical for reasons too involved to pursue here.
Yet a lot of Christians say that evolution is impossible, and that's going too far. The Bible never implies that evolution is impossible; it merely tells us that Adam (and Eve) did not evolve. (Sometimes people claim that animals reproduced after their kinds, but this is untrue: God created the various creatures "according to their kind," but that just means that he was producing species and sub-species.) In any case, evolution may well have happened since Adam or elsewhere in the universe, so if you want an evolved creature in a story--the next step in human evolution, for example, or an alien race that evolved--go for it. Just think through the implications.
Join us next time at the other end of scripture for "It's the End of the World!":
NOTICE: In the event of Christ's Return to Earth to set up his Kingdom today,
Pre-tribs will demand to be raptured out retroactively;
Post-tribs will say, "I told you so" but wonder where the Antichrist got off to;
Amills will smirk and say they've *been* the kingdom for nearly two millennia already;
Postmills will sulk and say the Millennium was over too fast for them to enjoy it; and
Idealists probably won't even notice.