By Dick Taylor
In a private facility just outside Des Moine, Iowa , primatologist Sue Savage-Rumbaugh is conducting an experiment that has lasted 26 years.
Danny Wallace investigates for Horizon
She's been rearing a small group of apes as if they are people, to see what happens.
Her results appear to be spectacular, at least to writer Danny Wallace:
"Kanzi asked me for a present. I gave him the free toothbrush kit from my flight over. He brushed his teeth. We bonded."
Danny is a seasoned television campaigner: he showed us How To Start Your Own Country on BBC Two last year.
As a non-scientist, he's a useful man to investigate the extent to which our closest relatives, the chimpanzees, could indeed be people, too. Because, at the heart of primate research, there is a conundrum.
Many primatologists are devising experiments that show chimps are ever more people-like than was thought just a few years ago; and yet, as scientists, they will not countenance that chimps could ever be people.
Yes and no
At the Yerkes Primate Centre in Atlanta, Danny finds out from researcher Victoria Horner that chimps have culture...
Victoria: "This experiment is the first definite evidence that chimpanzees can pass on ideas to each other. That is the basis of culture."
Danny: "So, are they people then?"
In Budongo National Park, Uganda. Katie Slocombe from St Andrews University is studying vocalisations with wild chimps...
Katie: "Chimps produce an incredibly wide range of sounds. It appears that they may have a rudimentary language."
Danny: "So, are they people then?
Alicia Melis of the Max Planck Institute in Leipzig conducts experiments to see if chimps have a quintessential human character, one that was thought to be absent till now: co-operation...
Alicia: "Chimps can co-operate, they can even chose the best co-operator to help them when presented with a range of their mates."
Danny: "...they co-operate, they're people?
Alicia: "Sort of!"
Researchers continue to find more and more human-like behaviours
Now, Danny's bluff character and native wit carry him through these encounters, but there is a good reason why he persists in asking these seemingly crazy questions.
According to philosopher Julian Baggini, it is possible that non-human animals like chimps could be people.
"You could say that an adult chimp has more of the characteristics of a person than a new born baby," he says.
After all, though humans and chimps are different species, they share up to 99.4% of their most crucial DNA (the figure is difficult to calculate exactly and depends on the scientist you speak to). And to prove how similar we are to chimps, Danny takes part in a potentially humiliating experiment.
The scent of male sweat is controlled by their genes, in both chimps and men. In a blind test, three women were asked to sniff the sweat of Danny and Cody the chimp, to see which one they fancied most.
When they found out afterwards that one of the odours was from a chimp, there was laughter. When they realised that two out of three had preferred the chimp, there was nervous laughter.
When Danny finally reaches Des Moines, the issue comes into focus.
The apes Sue Savage Rumbaugh works with - and lives with - are bonobos. They are a kind of chimpanzee that is less aggressive than that found in most zoos.
The chimp and human genomes are very, very close
Having brushed his teeth Kanzi, a 26-year-old bonobo, built like a heavyweight boxer and who is five times stronger than an average man, looks into Danny's eyes and asks him to play "Chase".
So they hang out together for a while, because that's what Kanzi has learned to do. And for Sue Savage Rumbaugh, learning is the key.
"Take a human child. If you lock him into a cage, never take him to the mall, never give him ice-cream, never teach him to communicate - how could he become a person?" asks Sue.
Chimps are human? Never. Chimps are people? You decide.
Horizon: Chimps Are People Too is on BBC Two at 2100 BST on Tuesday 10 October. Watch video highlights at Horizon's website.