|The Colbert Report||Mon - Thurs 11:30pm / 10:30c|
Stephen Colbert not only talks about gestures, he makes them throughout his talk. My favorite is the gesture accompanying the reference to a foaming mug of pinot grigiot.
One of the steady disputes on this blog concerns the role of gesture (hand signs) in language origins, so I always welcome new evidence on this issue. PlosOne has recently published a paper titled, "Chimpanzee Signaling Points to a Multimodal Origin of Human Language," by Jared Taglialatela, Jamie Russell, Jennifer Schaeffer, and William Hopkins. Alert regulars at Babel's Dawn may recall previous discussions of work by Taglialatela. He is investigating speech origins by studying chimpanzee brains and determining how language-ready the ape brain was. (See: Broca's Area in Chimpanzees?; Ape Cries are Complex; How Different are Ape Brains from Ours?) This latest paper argues that from the beginning human language has combined vocalization and gesture. That's in keeping my arguments on this blog, but how much confidence can we have in this latest work?
The region of the chimpanzee brain that interested the authors is in the left inferior frontal gyrus of the cerebral cortex, in Brodmann's area 44 and 45. This region has been previously identified by Taglialatela as a homologue of the human region known as Broca's area. It used to be said that Broca's area controlled speech. Today's understanding is more complex, but Broca's area is still considered critical for the motor output of language. The authors wanted to know if the role of this area in chimpanzee signaling.
The point of this research is to determine paths to speech. Possible scenearios are:
- Language began as a set of hand signals and later switched to speech. Evidence supporting this scenario would be activity in the chimp-Broca's area during gesture but not vocalization. Broca's area only began to control vocalizations after the last common ancestor of chimps and us.
- Language began as a set of vocal signals and later included gesture. Since apes are already gesturing and can learn to make words in sign language, it is hard to imagine what brain evidence might exist to support this scenario.
- Language began by combining gesture and vocalization. Supporting evidence would be that vocalization increases activity in the chimp-Broca's area, indicating that the human-lineage brain was already to control voluntary vocalizations at the time of the last common chimp/human ancestor.
The authors conducted a series of experiments to determine conditions that activate the chimp-Broca area. They used four captive chimpanzees, two who make the ahem vocalization and two who don't. The chimps were fed a substance that makes it possible to determine metabolic activity in the brain. They were then, individually, put in a position to try to catch a human's attention and beg for food. Finally, the chimpanzees were given PET scans to determine recent metabolic activity in the brain.
The two chimpanzees that vocalized as part of their effort to get human attention showed an increase metabolic activity in the chimp-Broca's area, while the two that relied on gesture alone did not. The authors interpret this finding as supporting scenario 3, language began by combining vocalization with gesture and does not support scenario A, that language began as gesture alone.
Their point is that we know the last common ancestor gestured because both humans and apes gesture. Now we know that the last common ancestor also had a region of the brain that was important to voluntary vocalization and is now important to speech. Thus, there is no reason to argue that language began with gesture because that's the only thing one could do with an ape brain.
There are a number of commenters on this blog who defend the gesture-first origins of language. Am I now saying it is time for them to go quiet? Not at all. Let's look at the possible objections to this paper:
- Chimp vocalizations are hard to classify. What's the difference between ahem and the ordinary chimp bark? The authors point out that attention-getting calls "have a clear recipient." They are much closer to the speech triangle, with a speaker and listener, lacking only a topic. It is often possible to distinguish a chimp ahem in this manner although it is not always easy, and there is plenty of room for wondering about interpreting particular sounds. But the point that is hard to overcome is that while all four subjects made vocalizations, only two made vocalizations that were interpreted as ahem sounds and only those two showed extra activity in their chimp-Broca's area.
- The logic isn't tight. The evidence 'supports' a scenario. It doesn't prove it. It is like an expert testifying that some piece of evidence is consistent with the prosecution's case. As somebody who has sat on many juries I like the evidence to be evidence of something. At the same time, it looks like the evidence does at least knock down a piece of anti-speech evidence. It gets rid of the argument that apes cannot make voluntary vocalizations and therefore an ape brain cannot get you started speaking.
- Then why don't apes do more voluntary vocalizing? Some skepticism is allowed just because of the surprising nature of the finding. It suggests apes could be doing more attention-getting vocalizing than they do, so what's keeping them mum? I've gone over this point many times on the blog. This evidence is just the latest in a long line of details that suggest apes could engage in at least protolanguage, yet they don't. The crucial change was in their sociability, particularly their willingness to trust, not in their intelligence or brains.