Just stumbled upon the scientific study where they raised a human child with a chimp

[DBoon]

4. a reference that doesn't give Elon Musk clicks

https://www.smithsonianmag.com/smart-news/guy-simultaneously-raised-chimp-and-baby-exactly-same-way-see-what-would-happen-180952171/

On June 26, 1931, comparative psychologist Winthrop Niles Kellogg and his wife welcomed a new arrival home: not a human infant, but a baby chimpanzee. The couple planned to raise the chimp, Gua, alongside their own baby boy, Donald. As later described in the Psychological Record, the idea was to see how environment influenced development. Could a chimp grow up to behave like a human? Or even think it was a human?

...

They raised the two babies in exactly the same way, in addition to conducting an exhaustive list of scientific experiments that included subjects such as "blood pressure, memory, body size, scribbling, reflexes, depth perception, vocalization, locomotion, reactions to tickling, strength, manual dexterity, problem solving, fears, equilibrium, play behavior, climbing, obedience, grasping, language comprehension, attention span and others," the Psychological Record authors note.

For a while, Gua actually excelled at these tests compared to Donald.

...
The experiment, however, ended rather abruptly and mysteriously. As the Psychological Record authors describe:

Our final concern is why the project ended when it did.

We are told only that the study was terminated on March 28, 1932, when Gua was returned to the Orange Park primate colony through a gradual rehabilitating process. But as for why, the Kelloggs, who are so specific on so many other points, leave the reader wondering.

It could be that the Kelloggs were simply exhausted from nine months of nonstop parenting and scientific work. Or perhaps it was the fact that Gua was becoming stronger and less manageable, and that the Kelloggs feared she might harm her human brother. Finally, one other possibility comes to mind, the authors point out: While Gua showed no signs of learning human languages, her brother Donald had begun imitating Gua's chimp noises. "In short, the language retardation in Donald may have brought an end to the study," the authors write.