Chimpanzees Become Much Smarter but Cannot Speak... Why is That?

In science fiction (SF) movies or novels, language is often treated as a major theme or motif.

In the movie 'Avatar', the Na'vi of the alien planet Pandora speak a unique language. 'Na'vi' is a language developed at the request of director James Cameron by Professor Paul Frommer of the University of Southern California.

The story of communication with aliens who come to Earth in a spaceship is depicted in 'Story of Your Life', which was made into the movie 'Arrival'. In this short story written by Ted Chiang, the protagonist, a linguist named Louise, learns the alien language and script while communicating with the aliens. After understanding the alien script, Louise gains the ability to see the future.

SF set on Earth sometimes imagines a scenario where chimpanzees become more intelligent than humans. In this case, chimpanzees learn the inferior human language rather than creating their own unique language as they evolve. This is a hypothetical scenario, so it is not necessary to question that premise while enjoying the visuals.

Even if they become smarter, monkeys lack 'language hardware'

If aliens exist, they would speak in their own language. (This is tautological. An 'alien' at the human level or a higher life form would have developed language long ago.) However, the possibility of 'chimpanzees speaking like humans' is very slim. This is because chimpanzees cannot produce as many varied sounds as humans physically. They lack the language hardware.

Humans have a larynx that includes vocal cords located lower than those of chimpanzees and other mammals, allowing them to utilize the space created to express various types of sounds. However, chimpanzees, with their larynx positioned higher, cannot produce multiple consonants and vowels like humans. Other primates and mammals also produce monotonous sounds due to the position of their larynx.

'Ontogeny recapitulates phylogeny.' This was once a widely accepted claim in biology and sociology. German zoologist Ernst Haeckel (1834–1919) stated this. Haeckel illustrated that the evolutionary history of all life forms on Earth is represented in the embryonic development process. Later, it was revealed that this illustration was manipulated, and the claim was discarded by the scientific community.

The reason babies make short tongue sounds

However, in the human larynx, there is a pattern where some aspects of evolution are repeated. Until humans reach a certain age, their larynx is positioned almost at the same height as the tongue, similar to chimpanzees (Lee Eun-hee, The Reason Only Humans Can Speak, Pressian, 2005.10.21.). Because of this arrangement of the mouth and larynx, even if a baby's intelligence develops rapidly, they cannot express their intentions vocally. As the baby grows, the pharynx, the passage between the mouth and larynx, lengthens, gradually lowering the position of the larynx. This allows them to acquire the hardware to produce diverse sounds, starting with 'short tongue sounds' and eventually achieving accurate articulation.

The language ability gained from the lowering of the larynx comes with risks. There is a risk of food getting stuck in the throat. Accidents involving food blocking the airway occur particularly frequently in humans. While other animals have separate passages for food and air, humans share the passage from the pharynx to the larynx for both food and air.

Humans took on the risk of choking while acquiring language

The epiglottis plays a role in preventing food from entering the airway. When swallowing food, the larynx rises, and the epiglottis covers the entrance to the airway. This action, which protects the airway from food, takes about one second. If one tries to speak while eating, it can lead to a minor accident known as choking. If a larger piece of food goes down the airway, it can result in a more serious accident.

Daniel Lieberman, a professor of human evolutionary biology at Harvard University, explained this as a risk acquired with language ability. Professor Lieberman stated in 《Our Body's Chronicle》 that “deaths from this cause occur more frequently than one might think,” and “in the U.S., choking deaths from food are about one-tenth of those from car accidents.”

Now try swallowing your saliva. You can feel the larynx rising and the epiglottis blocking the airway. At the moment the airway is covered, you cannot breathe. Compared to us, dogs do not need to protect their airway separately while eating. Therefore, dogs can breathe while eating and eat while breathing.

No one knows where the branches of evolution will extend. One might imagine, 'Could chimpanzees, in hundreds of thousands of years, lower their larynx position and produce varied sounds?' I would respond, “It is possible, but the likelihood is extremely slim.”

It is presumed that the lowering of the human larynx was influenced by bipedalism and locomotion. While it cannot be said that most animals that hold their heads upright have a lower larynx position, animals like chimpanzees that tend to keep their heads forward are less likely to take that evolutionary path. The fact that the larynx of chimpanzees has not lowered over the past several million years is evidence of this.

Some may have worried about the dominance of chimpanzees after watching the 'Planet of the Apes' movie. This is a misconception, and one reason is that chimpanzees cannot physically use language, and therefore cannot achieve advanced thinking through language. The beings humans should be wary of are not chimpanzees but humans. More closely, it is ourselves who can speak and think highly (?).