I'm writing a short story where a group of explorers found a mysterious cave in a remote jungle , Inside the cave they find strange paintings of spirals resembling portals , after exiting the mysterious cave the group noticed that the trail markings they made outside the cave had disappeared and that their GPS could not pick up any signals leaving them completely lost , they eventually came to the realization that the mystical cave was in fact a portal that took them back one million years in the past.
while in the jungle they got captured by a tribe of Homo-erectus ape people who forced them to become part their tribe. After blending with the tribe the group of explorers had successfully learned their language and taught the tribe the basics of agriculture and stone masonry. After passing down this knowledge the explorers were idolized as gods by the ape people. One of the explorers named "kevin" was also forced to become the new tribe leader , a role which he accepted. After some time one of the female explorers had re-discovered the mysterious cave , filled with excitement she quickly rushed back to tell the others. After she told everyone about the cave, Kevin who was now the leader of the tribe ordered the ape people to kill the explorers. In a dramatic scene the female explorer managed to escape and eventually ran back into the cave.
As she finally passes through the portal again and traveled back to the present her reality suddenly shatters infront of her eyes as modern civilization was now dominated by ape people , giant temples and statues of Kevin has been built across the planet. The world she once knew was gone forever ,the end.
Realistically would homo erectus manage to create a civilization like us if they recieved a little "help" or would they still be stuck in the stone age?
And also what is the brain capacity or body to brain ratio needed to build a civilization?