We don’t know what changed, really: was it better brains or harsher environments? Look at us: all the stories we’ve told with such confidence about inhuman civilizations on other Earths, and we remain absurdly ignorant about our own origins. Those proto-humans had a tool revolution, though. Clearly someone looked at the flint and hammerstone they were holding one day and thought, What if I did it like this…?

Perhaps that’s where the first group who truly feel like our ancestors arise. Half a million years ago, a handful of our world’s denizens transformed from somethings into someones. And we have their bones, their teeth, a few trackways and their tools.

Those trackways took them outwards, away from the grasslands of their homes. They spread into other continents and changed to meet the demands of climate, diet and experience. They mythologized their journeys and their ancestors; they added a dimension to the mundane world to account for all the things they felt and believed—and needed to believe but could not see. And they died and grieved and loved, just as we do.

At some point they crossed into Europe and met harsh winters and monstrous long-haired beasts. Cut off from their past, they became something different. Privation moulded their interactions, and yesterday’s mammoth hunt became tomorrow’s pantomimed performance before the fire. The world chipped at them like a flint until they were a sharp enough blade to unseam it and use all its component parts.

Even then, perhaps, they knew that there was more. They felt it, at certain places, certain seasons. There were places you did not go casually that could transform you or vanish you away. There were valleys where monsters might brush your elbow, from the other side of a divide incomprehensible to the human mind. There were clawed tracks that led off in directions they had no name for, into impossible distances as though whole worlds were held within the cracks of a cliff. Or foreign seas were folded into the inch-deep waters of a puddle. They sensed these spaces, we suspect, and there was value in knowing what places to avoid, or perhaps what places might offer inexplicable warmth in the hard ice-age winters. So this sense was honed by time and the passage of generations.

And of course there were the others that shared their world, in case all this wasn’t uncanny enough.

Our ancestors couldn’t have known how unusual their timeline was, to birth two sentient species. Only the isolationist icthyans truly shared their Earth with another thinking species for long—that we know of—and their mental and geographical worlds were so different. There was nothing for them to compete over, no way for them to threaten one another until the bitter end.

But for us, there was always a ghost waiting in the dark places.