Human nature and an undiscovered civilization are at the core of the Super-Sons tale in World’s Finest 222(March/April 1974), by Haney, Dillin and Vince Colletta.
Rival scientists argue over whether humans are inherently good or evil, and this argument spills over with the Super-Sons and their fathers, Superman having faith in people, and Batman thinking that no one is to be trusted.
That contrast could be the core of a really interesting story, but this tale pushes it to the side as the scientist with no faith in people goes out of his way to push the “savages” towards conflict. The boy that the Super-Sons befriend sacrifices himself to save others, showing that all are essentially good. Too easy.