A foundational question in understanding behavior is the degree to which it is shaped by inheritance versus environment. To explore this, some early 20th-century scientists conceived of unorthodox experiments. One of the most notable involved raising an animal and a human child together in a single household. This approach offered a unique, if controversial, window into the interplay between nature and nurture.
The Gua and Donald Study
In 1931, comparative psychologists Winthrop and Luella Kellogg embarked on a radical experiment to test the effects of a human environment on a non-human primate. They brought a seven-and-a-half-month-old female chimpanzee named Gua into their Florida home to be raised identically to their own son, Donald, who was ten months old.
The Kelloggs treated Gua as a daughter and sister, not a pet. She wore clothes, sat in a highchair for meals, received hugs and kisses, and was potty-trained alongside Donald. The Kelloggs meticulously documented the developmental progress of both infants through daily tests, measurements, and extensive notes. Their hypothesis was that a human-centric environment could cultivate human-like behaviors in an ape.
What the Kelloggs Discovered
Initially, the experiment seemed to support the Kelloggs’ hypothesis. Gua’s development in some areas outpaced Donald’s due to her greater physical maturity. She was quicker to master motor skills like using a spoon and walking upright, and she learned to respond to dozens of verbal commands.
Gua also showed behaviors associated with human children, such as giving kisses for affection and recognizing herself in a mirror. These successes, however, were matched by clear limitations. Despite efforts to teach her to speak, even manipulating her lips to form words, Gua never learned to vocalize human language and her communication remained limited to chimpanzee sounds.
The most unexpected outcome was the experiment’s effect on Donald. As the months progressed, he began to lag in language acquisition and started to imitate the sounds he heard from his chimpanzee “sister.” He adopted Gua’s food bark and other chimpanzee-like screeches. Donald also began copying some of Gua’s physical behaviors, such as biting people.
The Abrupt Conclusion
The Kelloggs grew concerned when Donald began adopting chimpanzee vocalizations instead of developing human speech. Realizing the environment was hindering their son’s development, they abruptly terminated the experiment after just nine months on March 28, 1932.
Following the experiment’s conclusion, the two were permanently separated. Gua was sent back to the primate center in Florida. Removed from the only family she had known, her health declined, and she died from pneumonia less than a year later. Donald’s development, once removed from Gua’s influence, returned to a normal trajectory and he went on to live a typical life.
The Experiment’s Scientific and Ethical Legacy
The Kellogg experiment left a lasting mark on developmental psychology. It provided evidence that while environment can shape behavior, it cannot override innate biological predispositions. Gua’s inability to learn speech, despite her upbringing, suggested that the capacity for language is a uniquely human biological trait.
From a modern perspective, the experiment has serious ethical problems. Raising a child in a setting that negatively impacted his development would be unacceptable today due to the potential for psychological harm. The emotional toll on Gua, who was raised as a human and then suddenly removed from her family, was also substantial. The lack of consent and the distress inflicted on both subjects ensure such a study will never be repeated.