Back in the 1930s, a human baby aged just 10 months old was forced to grow-up alongside a chimpanzee, but the experiment had tragic results.
Animal psychologists Winthrop Niles Kellogg and his wife Luella raised their son, Donald, alongside a chimp named Gua, who was seven-and-a-half-months old when she joined the family.
In what people have called a 'disturbing' experiment, the pair were treated as 'brother and sister', wearing baby clothes, eating in high chairs and having a kiss goodnight before bed.
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"What would be the nature of the resulting individual who had matured... without clothing, without human language and without association with others of its kind?" Winthrop wrote in his book, The Ape and the Child.
According to reports, for nine months, the couple conducted tests on Gua and Donald, reportedly for hours each day.
One saw the pair being spun around in chairs until they began to cry.
"The basic question was, is a chimp a chimp because it has chimp genes or because it is raised by other chimpanzees?" writes Theodore Dumas, in the Adult Health and Early Life Adversity: Behind the Curtains of Maternal Care Research.
"Thus, if baby Gua grew up to be very chimp-like in a human household, then genes win. However, if baby Gua grew up to be more human than chimp, then environment wins. As such, Gua was treated like Donald’s sister and underwent the same bathing, dressing, and feeding processes."
The test was due to last five years, but the couple ended up having to cancel the experiment early after concerns that Donald was showing worrying behaviours, such as grunting for more food, wrestling with Gua and even biting.
Other theories suggest the parents became concerned that Gua may one day harm Donald as her strength increased with age.
Sadly, both Donald and Gua had a tragic ending.
After the experiment was cancelled, Gua was sent away, from what was essentially a loving family environment to a 'relatively barren cage'.
"This was the second time she was stripped from her 'mother/caregiver' and she went from a warm affectionate family life to a relatively barren cage with other strange and not so well-behaved chimps," said Dunas.
"She died less than a year later, circa her third birthday, of a broken heart (the official cause of death was determined to be pneumonia)."
Meanwhile, Donald sadly died in 1973 at the age of 43. He is believed to have taken his own life one year after his parents passed away.
Lucy Devine