Welcome to brain Stuff production of I Heart Radio, Hey brain Stuff, Lauren vog obam here. Back in the nineteen sixties and seventies, it was all the rage with primatologists to conduct studies in which infant chimpanzees were raised as though they were human infants. This practice tested the limits of what a non human primate could accomplish if raised in human society, aiming to parse what was nature and
what was nurture. These studies often played out like dark fairy tales, with chimp babies growing up into tragic half humans, living between two worlds and belonging to neither. But one thing that came out of these studies was the realization that although these chimpanzees raised in human environments learned how to behave in eerily human ish ways, none of them could ever be taught to talk. We spoke with Asif Zanfar, a professor of psychology at the Princeton Neuroscience Institute. He said,
I think that surprised a lot of people. They weren't even producing rudimentary words a drunk person would say. According to Susan Far, that led researchers to develop a few theories about why this could be one that other primates might have the brains to produce speech, after all, they can do rudimentary symbolic communication, but they're lacking the vocal
anatomy to make speech sounds. Two that primates completely lack the neural control to produce speech sounds, or three that they lack both the proper brain and the proper anatomy for speech. Around this time, linguist and cognitive scientist Philip Lieberman tried to determine which, if any, of these conclusions
were true. In a nineteen sixty nine study, Lieberman and his co authors examined cadavers of Reesis monkeys to estimate, based on their anatomy, what speech sounds they could theoretically be able to make. A Lieberman's conclusion was that, based on the anatomy of a reesis, they wouldn't be able to speak even if their brains were wired just like ours.
Based on this study, the idea took hold that one of the main reasons chimps and other primates can't speak is that they lack the vocal anatomy to do so. But now half century later, a study published in Science Advances has revisited the question of why monkeys can't talk, and it debunks Lieberman's notion that monkeys lack the appropriate vocal anatomy. Instead, they say, monkeys mouths and throats could form human sounding words, but their brains aren't good enough
to tell their body how to do so. Sasan Far and an international team of researchers captured X ray video of a resis eating, squawking, and making facial expressions, then made a model of those movements that could predict the potential vocal range of the animal. They found that anatomically speaking, a resis has everything it needs to form entire sentences of human speech, although its voice definitely wouldn't sound human.
What it doesn't have is the necessary neural ability to coordinate respiration, oral facial muscle control, and laryngeal tension, all things we have to do in order to talk. In fact, sizan Far says, all of the old World primates, all the species in Africa and Asia, including the great apes, probably have the same ability. They conclude this because these monkeys and apes in large part have very similar vocal
and facial expressions. Why humans got such a tricked out brain in comparison to our primate relatives is hard to know, but it's fun to think about. Sison Far said, nobody's sure what driving forces and pressures lead to humans elaborating
a more sophisticated control of the vocal anatomy. Maybe as group size increased, it became inefficient to communicate via physical grooming, and you had to maintain relationships with many individuals, so the burden to maintain those relationships was shifted to the vocal acoustic domain. But to address what we all really want to know here, how feasible is a Planet of the Apes scenario? Sison Far said, Well, I don't know, but the new version of Planet of the Apes got
it right. In the first movie of the new series is the chimpanzee was given a drug to enhance its cognition, giving it the ability to speak. They didn't even address vocal anatomies, so they accidentally got it right. Hollywood is president sometimes. One theory about why humans have more communicative and vocal learning capabilities than other primates is that a lot of our brain development happens out in the world
rather than in utero. According to Zampar, the brain of a human infant is only developed at birth, while that of a Reese's Monkey is about six developed at birth. Today's episode was written by Jesslyn Shields and produced by Tyler Clang. Brain Stuff is a production of I Heart
Radio's How Stuff Works. For more in this and lots of other brainy topics, visit our home planet, how stuff works dot com and for more podcasts from my heart radio is the heart radio app, Apple Podcasts, or wherever you listen to your favorite shows.