The emergent humans were still animals, still bound by natural law. No innovation in the way they lived would have taken root if it had not given the… - Stephen Baxter

On the longest of timescales, over millions of years, the workings of chance defied human intuition. Humans were equipped with a subjective consciousness of risk and improbability suitable for creatures with a lifespan of less than a century or so. Event that came much less frequently than that—such as asteroid impacts—were place, in human minds, in the category not of rare, but of never. But the impacts happened even so, and to a creature with a lifespan of, say, ten million years, would not have seemed so improbable at all.
Given enough time even such unlikely events as ocean crossings from Africa to South America would inevitably occur, over and again, and would shape the destiny of life.

Bex shrugged. “You think anybody’s going to listen to a bunch of scientists? No offense. But nobody has so far.”

But what would humans do, she mused, if they stumbled on a situation like this?
Well they wouldn’t be satisfied with the generosity of Candyland. They’d breed until the caves were overflowing. The hunters would start ranging farther until all the animals in the area were eaten or driven away. Then agriculture would start, with everybody forced to bend their bodies to back-breaking toil, day after day. As the population exploded the forests would be cut back, the animals decimated.
Then would come the famines and the wars.