THAT'S what was missing here! Wanderer, my friend, you don't know what you've started now! Hang on to your Barsoomian hat!
The mind of Edgar Rice Burroughs was a well of adventure, imagination, and WEIRDNESS. For one thing, he had a profound hatred of aging; so most of his prominent stories feature something that counteracts old age. Even Tarzan, who was more real-world-based than John Carter or Carson Napier, discovered a "Fountain of Youth" which kept him and Jane young while their son Korak was growing up to manhood.
Yes, I said son. And I do mean a biological son. Which leads to the fact that Burroughs wasn't the only weird one. When it came to Tarzan, moviemakers were MORE weird.
In our time, there is way too much of a green light given to fleshly desires. But at the time the early Tarzan movies were being made, the opposite problem existed: even acts of desire and pleasure WHICH ARE FULLY APPROVED OF BY GOD HIMSELF IN SCRIPTURE, could be looked on as "dirty" by some who were involved with cinema. Now, although Mr. Burroughs did not, ahem, always have his characters remain perfectly chaste, he DID very clearly establish in the Tarzan series that Tarzan and Jane got lawfully married by clergy. So there was NOTHING objectionable in their living together as the MARRIED couple they were. But the early Tarzan movies wouldn't even let them have that. In an incredible display of fatuous absurdity, they depicted Tarzan and Jane merely living as NEIGHBORS in separate tree houses, not even sleeping under the same roof! It followed that the only way they could experience anything like parenthood was to foster an orphan: hence the character of "Boy" replacing Korak, the natural-born son of Tarzan and Jane.
Thinking of this nonsense, and then of the opposite nonsense we have today, I am reminded of Martin Luther's observation that human nature is like a drunken man on horseback-- who may fall off on either side.