"Apes communicate, humans have language"
Mrs Friederici, why do only humans have language?
This is still unknown. We assume that it is because language is assigned to certain brain structures that are developed differently in humans as opposed to apes, and that these developments are based on genetics.
Apes are also able to communicate with each other. What’s the difference between this and human language?
That’s true, apes and even dogs and parrots are able to learn words. Thereby they associate an abstract symbol or an acoustic stimulus with an object. Single words by no means make a language. They just make sense if they can be matched in endless numbers of combinations by following fixed rules. Animals don’t succeed in doing this, not even our closest relatives. Apes can communicate, but humans have language. Admittedly, we still know less about the brain structures in apes that enable language in humans. They are hard to investigate.
Why?
For two reasons. It’s not possible to give language tasks to apes and watch the active brain structures in the MRI scanner, as it is done with humans. Furthermore, due to their highly complex behaviour and their risk of extinction there are very strict ethical standards in place to protect them.
Today’s knowledge is therefore mostly acquired from chimps in zoos. But they possess a very limited "vocabulary", meaning a significantly less developed communication system than chimps in the wilderness. Wild chimps show quite complex combinations of vocalisations. We would like to figure out how brains that produce tones evolve into brains processing human language.
How do you want to investigate that?
Together with the MPI for Evolutionary Anthropology (MPI EVA) and several animal reserves in Uganda, Gabon, the Ivory Coast, and Congo we want to find out how the behaviour of wild chimps is related to their brain structure. Over the last few years scientists have observed how these animals communicate with each other. If one should die of a natural cause, due to age or a fight with a conspecific, we investigate the anatomy of its brain with the help of MR imaging. How are the structures shaped, which are responsible for language in humans? From that we would like to determine what happens to the apes’ rudimentary communication structures in order to allow humans to use language? Which structures and connections make the decisive difference between apes and humans?
One decisive brain structure for language is the so-called arcuate fasciculus: a fibre tract that you explored some years ago. This tract doesn’t exist in apes. Could that be the "missing link" you’re looking for?
In humans, a crucial fibre bundle of the dorsal pathway (Arcuate Fasciculus (AF) in violet) strengthens over the course of life and links the two central language areas: Broca's area (region 44, 45) and Wernicke's area (region 22). In small children (C), the AF only links the areas for sounds and movement. Later, with the beginning of language ability (A), it connects these two language areas and extends significantly further into the temporal lobe (including regions 21, 37). In contrast to humans, the AF is generally less evolved in monkeys and apes (B). The second main connection between Broca's and Wernicke's areas, the ventral pathway (orange), is less variable in its development and is equally evolved in humans, apes, and monkeys.
In a way, yes. In humans the arcuate fibre tract connects Broca’s area, which mainly processes grammar, with Wernicke’s area, which is mainly responsible for word meaning. Both regions can exchange information along this tract. In chimps you can only find the beginnings of this structure.
Up to now, things like this could only be investigated in animals living in zoos and with low resolution images, instead of in wild animals and with highly detailed images, as are possible today. Many structures of the chimp’s brain, which is much smaller, have not been examined yet. It’s especially unclear into which brain areas these fibre tracts send their data. Furthermore, we would like to determine if the arcuate fasciculus is indeed the crucial difference in humans – or if it’s perhaps more developed in wild chimps, as we assume, and therefore not the most important distinctive feature.
To what extent do the brains of apes resemble those of human toddlers, before they’re able to understand and form language?
Indeed, this specific fibre tract between Broca’s and Wernicke’s areas is equally underdeveloped in apes and toddlers. In humans, a process called myelination begins. By using the fibre tracts an insulating sheath is built up. This allows information to move faster between these processing areas and the linguistic capabilities can develop. Thus, the tract exists in humans right from beginning, but it's not yet functional.
Languages are mixing up and bilingualism is increasing. Are these modern linguistic changes also reflected in our brain structure? Is a microevolution taking place?
We know that every language leaves its traces in the general neuronal language network, it doesn’t matter if it’s German, English, or Chinese. This depends on certain demands. Languages with a fixed word order, such as English, shape the brain structures in a different way than languages with a free word order, such as German. At the moment we're still determining the impact of these factors. There isn't really a kind of microevolution taking place as all languages operate on the same general brain networks.
Why is it that you want to know where language comes from?
Even the early philosophers wanted to know what distinguishes man from animal. The question has preoccupied science until this day. Most things people are capable of animals can also do, even solving complex problems. Language stands out as a real unique feature of humans. If we want to know more about it, we need to hurry up. There are no ape species left that are not currently threatened by extinction.
The interview was conducted by Verena Müller.
About the project: "The Evolution of Hominoid Brain Connectomics"
Although it is known that language is a purely human ability, it is not sufficiently clear why that is. At the MPI CBS and the MPI EVA neuroscientists and primatologists work together in an attempt to decode the structural evolution of the primate brain, to specify the primate connectome, the entirety of neural connections in the brain. Furthermore, for the first time, the researchers will compare the language-like skills between individual groups of non-human primates and also individual animals with their brain structures. Some groups are significantly more communicative than others, just like animals in the wild than those in captivity.
To do this, the researchers use MRI data from animals that have died naturally and link them with sound and video recordings of the animals. By doing so, they will try to determine whether particularly communicative animals show more highly developed structures. It may even turn out that some of the prominent brain structures are much more developed than previously assumed. Only then can it be explained what the actual human characteristics of the brain are.
