This Wikipedia link says,

Sign language and computer keyboards are used in primate language research because non-human primates lack vocal cords and other human speech organs. However, primates do possess the manual dexterity required for keyboard operation.

If chimpanzees lack vocal cords like humans, how was Caesar able to speak in the movie?

The cognitive ability of Caesar to learn language is taken care of in the movie. But the physical ability of Caesar to speak is unclear to me.

  • 3
    He whispered. You don't need vocal chords to whisper. Aug 8, 2011 at 20:47
  • @OghmaOsiris I don't think you can whisper without vocal cords. Dec 30, 2011 at 15:55
  • 3
    @RoyalFlush: Regardless, you can. Aug 25, 2014 at 11:19

5 Answers 5


Apes do have vocal cords. The Wikipedia quote in your question is incorrect and/or outdated. It has since been changed to (it also has reference links backing up these changes):

Sign language and computer keyboards are used in primate language research because non-human primate vocal cords cannot close fully, and they have less control of the tongue and lower jaw.

So I'd say they are pretty close to being physically able to speak. But remember Caesar was mutated by the ALZ-112, which could have further developed his vocal cords and his ability to speak.

He doesn't speak in the movie until he confronts the caretaker (when he yells "No!"), and that happened after

Caesar broke into Will's house, stole the ALZ-113 and released it into the cages while being exposed to this new and more aggressive virus himself. This might have been just what he needed to gain the ability to speak.

The fact that Caesar learned to speak but the other apes also exposed to the new virus didn't can be explained by previous mutations caused by the ALZ-112 which were also necessary (ie: ALZ-112 + ALZ-113 => speech; just one of them => no speech).

  • Your last point in the spoiler is somehow refuted in the Dawn of the Planet of the Apes, as more apes are shown speaking. Apr 17, 2015 at 6:49
  • 1
    @AlfredoHernández The question was, how could Caesar physically speak. Royal Flush's answer convincingly answered that question. Your comment is actually a very good question itself...
    – Morgan
    Feb 15, 2016 at 18:36

One theory is:

Caesar was born with genetic variations with more human like genes resulting in more human-like vocal cords. This genetic variation/mutation probably happened because his mom was given the ALZ 112.

According to this theory, Caesar's mom and all other apes (who got ALZ112) in the movie didn't have the physical ability to speak although they became intelligent. When these intelligent apes give birth to off-springs, the next generation apes are born with genetic variation resulting in a human-like physical ability to speak.

However, I am not entirely satisfied with this explanation.

  • 1
    a) The drug in question was not a gene therapy -- this is why they were not expecting Caesar to vertically inherit his mothers abilities. The inheritance appears to be epigenetic (en.wikipedia.org/wiki/Epigenetics), perhaps DNA methylation. b) The drug targeted the central nervous system, not anatomy. It would not have altered vocal chords.
    – HNL
    Dec 29, 2011 at 8:07

This article explains how humans talk vs. monkeys. Seems to come down to a longer larynx and shorter snout, making the vocal system more controllable and producing a wider range of sounds.

Looking at the movies, Caesar also likes to walk upright, has a "flatish" face... So I would assume the virus (which he is a second generation, so he could have more emergent traits than his parent) continued its evolutionary thrust and the speech goes along with the brain and other physical changes.

Perhaps eventually others will talk more, or perhaps the second and further generations will develop speech.

I'm also curious if the airborne ALZ-113 might mutate other chimps worldwide now since the humans have spread it... or there might be a more complex protocol for bonding it properly with the monkey's DNA.

Something also a bit off... Kobo is a bonobo, but he's violent and paranoid? Bonobos are the matriarchal, "peaceful" ones!


If one can collapse their airway to make sound come out, why can't others? I know it's possible because it's the only way I can really speak. I have no true or false vocal cords to use.


Very slowly.

Most of Ceasar's words in the movies are chosen carefully to be concise, and are spoken slowly. Caeasar also often chooses sign language instead of speaking.

This is consistent with an ape whose intelligence enables him to speak, but whose anatomical limitations require him to speak patiently and slowly.

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