Most people have seen at least one of the “Planet of the Apes” movies, whether it’s the original films from the late 1960s, or the latest release, 2024’s “Kingdom of the Planet of the Apes”. In the series, scientists develop an experimental drug called ALZ-113, initially intended to cure Alzheimer’s disease. When tested on great apes, the drug enhances their intelligence and enables them to speak. Meanwhile, the film portrays the decline in human speech as a side effect of ‘The Simian Flu’, caused by ALZ-113.
While talking apes are an intriguing fictional concept — and may remind some of the “Planet of the Apes” series — a more scientifically grounded explanation for apes’ inability to speak is worth exploring. Specifically, this article discusses the role of the epiglottis in this phenomenon.
The epiglottis, a flap of cartilage located above the larynx, prevents food and liquid from entering the windpipe when we swallow. As we swallow, our breathing temporarily stops to ensure food does not go down the wrong way — a mechanism that can be surprising when first hearing about it. In the early stages of human evolution, our vocal tract closely resembled those of other primates. However, as humans evolved our muzzle shortened, and the larynx descended, causing the epiglottis to no longer cover the soft palate, making it easier for food to block the airway and cause choking.
Apes, on the other hand, maintain an anatomical setup that allows them to breathe and eat simultaneously. Their epiglottis and soft palate remain connected, creating an intranasal airway. Apes also have vocal membranes — thin flaps of tissue near the vocal folds — but these features do not allow them to produce complex speech. Instead, apes vocalize by forcing air up their larynges, resulting in various sounds.
Although humans lost the ability to breathe and eat at the same time, these changes enabled us to develop speech. The larynx’s descent created more space in our mouths, allowing our tongue more room to move forward, back, up, and down. This flexibility helps us produce vowels and a myriad of other vocal sounds.
While the epiglottis is key to our ability to speak, it is just one element in the complex evolution of human communication. Factors like the alignment of our teeth, advancements in brain function, and social factors all contribute to our sophisticated speech abilities. For instance, our brain’s improved control over tongue movements enhances the accuracy of our speech. Moreover, social influences have driven the development of sophisticated speech. According to anthropologist and primate behavior specialist Robin Dunbar’s research, gossip might have evolved as a more efficient means of maintaining social bonds in larger groups, allowing our ancestors to manage complex social interactions and contributing to the refinement of our language skills.
And who knows? Maybe with a few more years of evolution, we might wake up one day to find apes discussing the latest human trends or sharing their insights on nature and life with us! Until then, we’ll continue to deal with the quirks and consequences of learning to talk — after all, it’s all a part of the unique journey of our speech evolution.
