How do human brains differ from ape brains? We know that our brains are a lot bigger, but so what? Presumably we are smarter, but how exactly? We divvy up the work between right and left brain hemispheres (“lateralization”), but what does that get us? For some years now Jared Taglialatela and his team have been delving into the question of ape brains and how they foreshadow human brains, and every so often this blog reports on their work (see, e.g.: Ape Cries are Complex). The March 11 issue of Current Biology includes the latest results of the team’s investigations (“Communicative Signaling Activates ‘Broca’s’ Homolog in Chimpanzees,” paper here). They have found evidence that brain structures “underlying language production in the human brain may have been present in the common ancestor of humans and chimpanzees.” Or, to emphasize the surprise, the brain’s “language areas” are older than language itself.
I am always suspicious of attempts to compare the “communication” of humans with those of another species because investigators can so easily put two different activities under the abstract terms communication or language. (In Dean Falk’s book recently reviewed on this blog, Finding Our Tongues, for example, she writes as though “body language” and speech were different modalities of the same thing.) However, in this case the authors have stayed in tune with this blog, which views language as the direction of joint attention toward a neutral topic. The “communication” tested in the reported experiments consisted of manual and/or vocal gestures made by adult, captive chimpanzees in an attempt to catch a human’s attention and direct it toward food. This activity is about as good a behavioral homology as we are going to get from non-language using species.
In the experiments a solitary chimpanzee saw a human come by and sit down with some food. The chimp tried to catch the person’s attention with manual or vocal gestures (typically, both) for two minutes, at which time the human would resolve the tension by giving the chimpanzee the food. Before this brief interaction, the ape was injected with a radioactive tracer substance and after the interaction the chimp was subjected to a PET brain-imaging scan to see what parts of the brain had been active during the interaction. A control test established how the brain image looks under similar conditions, but without the attention-catching part.
In human’s, the classic brain area for generating speech is Broca’s Area, which has a homolog in apes known as Brodmann’s Area, both of which are in a larger region of the brain known as the inferior frontal gyrus (IFG). The team’s work was not finely-tuned enough to specify whether the Brodmann’s area region of the chimpanzee brain had been activated, but it did demonstrate that the left IFG and associated subcortical regions had been activated during the communication. Although we will have to wait for more precise results, the work does show that chimpanzee efforts to catch and share attention are lateralized, as they are in humans, and have a special strength in the left IFG, as they do in humans. So what? So quite a bit, I believe.
I have changed many opinions in the course of working on this blog, but one that was stated in my first post has survived. I said then that we know from efforts to teach sign language to gorillas, chimpanzees, and bonobos that they are smart enough to use at least some simple language, and yet they do not. The explanation has to lie somewhere other than in our superior intelligence. From time to time a new piece of evidence comes along to support that proposition, and here we have the latest example.
The trend of the work coming out of Taglialatela’s team in Georgia shows that apes have the brain capacity to introduce the basics of language, joint attention. We are plainly smarter than chimpanzees, more able to concentrate on tasks for a long time, more imaginative, more able to calculate results, more attentive to the consequences of our actions, but apes share enough of our brain structure and capacity to do all those things a little. If that brain power was all it took, they should speak or gesture linguistically at least a little. Yet in the wild they do not have even a little language.
What’s the problem?
Well, what’s the problem with captive apes who are taught sign language? They learn a few words and can use them to their advantage, getting food and sociable tickles, but then they stop progressing. Linguists tend to explain the difficulties in terms of grammatical limitations. They don’t have the grammatical apparatus to put together richer sentences, but even if that is true, it is also true for children younger than three, and yet eighteen-month-old toddlers are much more advanced linguistically than sign-language-using apes.
Despite their intellectual parity, it is not hard to notice a very sharp difference between toddlers and apes of any age. The toddlers are far more communal, far more eager to notice what you notice, much quicker on the draw to report a perception of their own, mote ready to laugh when you laugh, more apt to be alarmed if you cry. Western civilization has not valued these things so much. The Greeks set us down the wrong path when they said it was reason that distinguished humans from the other species, and as was typical of Greek science the generalization was stronger on assertion than it was on evidence. We are a communal species, one whose richness comes by sharing in the wisdom of others. When apes discover a valuable truth, which they can occasionally do, they keep it to themselves, even if they have a way to spread the news.
We now have good, brain-scan evidence that the common ancestor of chimpanzees and humans likely already had at least some of the brain structure that had seemed specialized for language. The really critical difference was that these structures were not put to the community uses they have amongst humans today. The story of the evolution of language is a tale of the human lineage growing more communal more than it is a story of a species getting smarter.