I'm looking for a short story that involved:
- time travel;
- the search for the origins of humanity;
- an ancient enemy.
It was one of several short stories published in one of the monthly Amazing Stories that used to be popular so long ago (the 1970s for this particular tale).
The plot, inasmuch as I can recall, went along the following lines:
Historical anthropologists in the present use a time machine observe the very earliest homo sapiens. In their travels, they observe that although Homo sapiens are obviously related to our cousins in the evolutionary tree — Neanderthals and the like — Homo sapiens do not appear until much closer to the present than previously thought. They seem to just appear in the timeline all of a sudden.
As the search continues for the point in time when Homo sapiens makes their first appearance, the main character tries to understand why they would show up in suddenly in a rather short time frame compared to their evolutionary cousins.
The story ends when the main character realizes the obvious truth. Humanity did not evolve here. Humans were put here. A close friend of the main character reveals that it was all a test to see if Homo sapiens could grow and evolve to discover and understand their own origins.
Our progenitors had been locked in eons of war with creatures that can be described as Lovecraftian — immense monstrosities of unimaginable malice towards humans. It was a war our forebears were losing. They needed a way to wipe the slate clean, so to speak, and come up with a completely new source of strategies.
So they invented us. A small volunteer group of people had been stripped of everything, especially their memories. They were left on a fertile world with only the stone tools and basic implements to survive.
A small group of observers had also been planted on that world to document what happens. The main character's friend was the last of the observers. This observer was also immensely proud of humanity's ability to survive and innovate. In particular, they had been able to crack time travel, something the original species had never thought to try.
At the end of the story, the ancient enemy is out still there in the cosmos, waiting.