Chimpanzees might be able to understand human languages when spoken to them (when trained), but they can’t reproduce it with their mouths which are shaped much like those of humans. But you have seen many parrots imitate the sounds of human languages although their mouths are not shaped like a human’s at all.
What is the reason behind this? The following answers from four separate people are the highest rated explanations to this phenomenon on the internet.
How do birds make human sounds when their bodies are so different? The answer is that birds rely on vocalizations, so they actually have a very diverse set of noises they can make. Birds sing and chirp and hoot to relay all kinds of information, the way we make different noises with our mouth to mean “hello” or “danger” etc. The physiology of birds allows them to make most of the same sounds as us–however, there are sounds that they can’t make. Listen closely to this. The word “pick” actually comes out “kick”, but because there’s a subtitle and because pick makes more sense, your brain wants to hear pick.
You’re right on the money with lips: the sounds birds have trouble making are the sounds that require lips. But they use substitutes that are close enough that we might not notice. For “p” you can substitute “k”. For “m” you can substitute “ŋ” (the sound at the end of “thing”). Both of these sounds can be made without lips. Birds also tend to talk very very fast, which helps blur the words together enough that they sound right.
Why don’t chimps have this ability? Chimpanzees communicate mainly by gestures and facial expressions. They do make noises, but they’re not the most important part like they are for us. Chimps only have four distinct noises, “grunts, barks, screams, and hoots”. The way they distinguish meaning from these is how loud they are and whether they’re low or high pitched. So chimps don’t need the phonetic range that a human or a bird has. They don’t need their muscles to make the kind of complex sounds that humans use. Evolution made some changes to our anatomy that allow us to make a wide range of sounds, but chimps don’t need that so they never developed it.
In addition, phonetic range is a very use-it-or-lose-it skill. If a baby human is not made familiar with certain sounds, they will have a much harder time picking them up later in life. So even with the sounds a chimp might be physically capable of making, the chimp probably hasn’t trained their muscles to make it and will struggle with it.
Because primates like chimps communicate through gesture, they have actually been very successful at learning sign language. But their voices are only used for grunting and hooting, so it takes a lot more work for them to use words.
I’m an anthropologist, so I actually don’t know about the birds. But chimps can’t articulate language properly not because of their brains (they learn sign language quite well, indicating that there are no major cognitive issues) or really their lips, but because of the position of their voice box (larynx). In humans, the voice box is very low in the throat, allowing the space above the voice box to be a resonating chamber for sound. In chimps, the voice box is quite high, making it impossible for them to produce the full range of human sounds.
As an interesting side note, babies have high voice boxes too. As they grow, the voice box drops lower, allowing them to produce the full range of human sounds. Which is why sometimes you can teach your babies sign language, and they will communicate their needs. They WANT to talk to you– but they can’t because their voice box isn’t in the right place.
While chimps have been successful in learning how to communicate with many of the symbols of sign language, they have not been able to master some other aspects required for true language, like syntax. Most neurolinguists would agree that this is indeed because of differences in their brains that are reflective of differing cognitive capacity for language. ( Also, they learn this “language” much, much slower than humans and in different ways. )
So while bypassing the difficulties with articulation by using a gesture-based language does reveal an ability to learn symbols, it also reveals cognitive limitations in the ability of primates to learn language.
There’s two types of learning relevant to this discussion, auditory learning and vocal learning. Auditory learning is the simple ability to associate sounds with meanings. Chimps and birds are both capable of this, as is your dog when he “sits” on command. The more difficult task is vocal learning which is the ability to mimic sounds an animal has heard. This is actually a pretty rare skill, exhibited by only five mammalian classes (bats, cetacenas, elephants, sea lions and humans) and 3 avian classes (parrots, songbirds and hummingbirds) (Simonyna, Howitz & Jarvis, 2012).
The vast majority of other animals, unequipped with the ability for vocal learning, are only capable of producing those sounds innately encoded in their genome, usually primitive grunts, screeches, etc. Although the process of repeating a sound seems simple, it requires unique neurological hardware and is not a simple extension of normal auditory and motor faculties. Jarvis’ lab and others have been trying to map out these circuits in avian brains, which show unique gene expression (eg ZENK up-regulation). Again, vocal learning is not a natural extension of higher cortical processes; it requires special circuitry developed via evolution, not across an animal’s lifetime.
Together, auditory learning and vocal learning are considered the “substrate for language.” Language requires both processes. Without vocal learning, an animal cannot vocalize “learned” sounds. It’s stuck with the sounds it was born knowing. Without auditory learning, an animal cannot associate new meanings to novel sounds. It’s stuck with the associations it was born understanding. Combined, these forms of learning allow an animal to associate sounds with meaning and repeat those sounds, to “speak.” To be clear, when a chimp uses sign language, it is using motor learning (ie copying another chimp’s physical movements), which is vastly different than vocal learning (copying sounds). I cannot comment on differences between each animal’s vocal apparatus, but even if they were all the same, most animals’ brains would still be the limiting factor.
Summary: This is its own field of study. It is due to a difference in the animal’s brains, specifically the presence/absence of circuits designed for vocal learning. Vocal learning is the unique ability to learn how to mimic sounds an animal has heard. Across the animal kingdom only 8 classes developed this ability and they are from vastly different origins, separated by as much as 65-300 million years of evolution, implying that they achieved this skill convergently.
See this 5 minute video for a more comprehensive introduction to the subject: Vocal learning across species – Erich Jarvis
Lips are not the only mechanism to make certain sounds. Many different structures can create he same sound. Ever see an electric guitarist (e.g. Frampton) make his guitar talk? Birds have complex vocal apparatus that can create quite complex sound patterns. BTW, parrots do not just MIMIC human language – they truly SPEAK and understand human languages. I recently started writing down the English phrases one of my macaws uses and it ended up two pages long. These are phrases he understands and uses correctly in communication – not just mimicry. For example about an hour ago he was eating some grapes, he turned to me and said “want some of this?” and threw a grape at me. Seriously.