Thursday, July 31, 2014

Tough Talking Apes

Science vs. Hollywood is always good for a laugh, but it's often a chance to learn some very interesting tidbits as well. Today, let’s take on the talking apes of the new movie, Dawn of the Planet of the Apes. Sure, the apes with whom Charlton Heston discussed Baconian philosophy over a nice plate of bananas were capable of talking. They had been afforded many generations of possible evolution. But Dawn takes place only 10 years after the previous film, when Cesar and his cohorts escaped to live in the woods.

Cesar speaks in Dawn of the Planet of the Apes. This is
amazing and impossible. But what may be worse – he’s a
face painter! He would fit in at a hockey game or a
Seinfeld episode.
Is it possible that they could learn speech within one decade? Are apes just not trying right now? The grand question would be, why is it that humans are the only animals that use spoken language to communicate?

To begin to answer our questions, one first must decide what a language is. Linguists have four criteria for sounds to be a language. One, each vocalization has a certain order – the short "i" sound always precedes the "en" sound in the word “in.” Second, there must be an order to vocalizations – this is syntax. Third, the vocalizations cannot be tied to or defined by a specific emotional state – you can yell the word “Hey,” either to let someone know a bus is driving at them, or to say hi a friend you meet for coffee. And fourth, novel vocalizations are understood – you can say something that has never been said before, but those people listening to you will understand its meaning.

If sounds follow those four rules, then they’re an oral language. So humans have spoken language and other animals don't - although the majority of people don’t use the gift very well. But the question remains, why are humans so much better at making sounds and language than primates? We share 98% of our genes with chimpanzees, but they can make only three dozen or so vocalizations. Humans can make hundreds of different sounds – every noise required for every language on Earth. Where did we separate from apes in terms of vocalization?

Current hypotheses focus on two areas; brain molecular biology and body anatomy.  Let’s focus on the anatomy – we can make more vocalizations because of how our throats and chests have evolved.

The hyoid is the only human bone that is attached
to only muscles, not to another bone. Our hyoid is attached to 
tongue muscles, throat muscles, and jaw muscles. They all
work together to help us produce thousands of vocalizations.
To make sounds, you must be able to expel air in a controlled manner, this requires rib muscles and innervation to allow controlled exhalation – we got it, apes don’t. The air that is expelled passes over the vocal folds and vibrates them – this produces sound waves. The wave that is produced is based on the way your muscles change the shape of the vocal fold cartilage, and one way to alter the laryngeal muscle tone and shape is by moving your tongue.

The tongue is a muscle, and ours goes further back in our throat as compared to that of apes. Theirs is housed completely within their mouth, but we can change the shape of our voice box by using our tongue. You can stick out your tongue and move it side to side and feel your Adam’s apple move. Your adam's apple is NOT the same thing as your hyoid bone; the adam's apple is the laryngeal prominence associated with your voice box, but you can see that moving your tongue can modulate the vocal folds.

The other characteristic of the tongue that makes a difference is that it is our most sensitive touch appendage. We can make small and discrete moves with the tongue, and sense where it is in relation to our teeth and cheeks. This is another reason we can make so many different sounds, and is also why babies put everything in their mouths.

Another anatomical difference is that humans have a free-floating hyoid bone; it is the only bone in the human body that is not anchored to another bone. By attaching to the pharyngeal and tongue muscles, our hyoid helps us to make more than hoots and grunts. While apes do have a hyoid bone, it is not located as deep in their throat as is ours. In fact, infant (human) larynx and hyoid bone anatomy looks a lot like ape anatomy, but as we grow, our voice box and hyoid bone descend in our throat, while those of the apes do not. This is one reason it takes babies a while to learn to speak, muscle tone being another.

The intercostal muscles between the ribs are arranged
in several diagonal layers. The external muscles help with
inspiration, while the internal intercostals help with forced
exhalation. Humans have much more innervation of these
muscles (see the nerve traveling with the artery and vein in
Fig. B), so we can control exhalation for vocalization. It is
said that the human thoracic nerves allow for as much
control as the innervation of the hand and fingers.
Your rib muscles, your tongue attachment and your hyoid bone are all good reasons why humans can make more vocalizations as compared to nonhuman animals, but our brains matter too. The shear size of our brain means that we can devote more neurons to abstract thought, assigning meanings to vocalizations – this is the basis of a large dynamic language. But there is a molecular issue as well.

The Foxp2 protein is involved in vocalization and in understanding language. In songbirds with a mutated foxp2, their song is incomplete and inaccurate. In humans, defects in foxp2 activity lead to severe language impairments in both speaking and in understanding. Two small mutations in the human foxp2 are much of what separates our language ability from that of the apes.

A 2014 commentary takes the idea of bird song further, hypothesizing that human speech evolution was a reawakening of avian constructs in the basal ganglia of the brain, with the “tinkering” afforded by time, pressure, and mutation.

Terrence McKenna put forth a wild hypothesis in his 1992
book, Food of the Gods. His “stoned ape” theory stated that
early primates used psychedelic mushrooms to expand their
consciousness and that this led to fast evolution and
development of speech. If we follow this hypothesis, then just
what was growing in the woods where Cesar and his ape
mates have been living for the last 10 years?
Cesar of the Apes movies was genetically modified for intelligence, so maybe he had the foxp2 necessary to grasp speech. But do you think part of his genetic modification was to alter his ribs, hyoid, mouth, and tongue? The foxp2 does work in vocal fold, soft palate and tongue function, but it doesn't move your hyoid around!

If not, then maybe he understands our language, but he won’t be speaking it. And what about his cohorts? They speak too, although nobody played molecular hanky panky with them. And all this takes place within the lives of this single generation! The 1968 movie had time on its side, the evolution through generations was at least plausible. (but why did they speak English?)

For the new movie, it isn't evolution they so, it isn’t even evolution on steroids. The talking apes toss out Darwin completely and smell of Lamarckian evolution meets the Hulk (see this post). Come on Hollywood, give us a little credit – if you want us to buy in to a world we recognize, then stick to the natural laws we know.

Contributed by Mark E. Lasbury, MS, MSEd, PhD
As Many Exceptions As Rules 

Ackermann H, Hage SR, & Ziegler W (2014). Brain mechanisms of acoustic communication in humans and nonhuman primates: An evolutionary perspective. The Behavioral and brain sciences, 1-84 PMID: 24827156

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