With our descended larynx, we have a much longer vocal tract, enabling us to produce a much greater variety of sounds. Coupled with this extra-long sound pipe, we also have greater muscular control over our lips and tongues compared to other primates, which is why human speech is physically impossible for other animals. But that physical limitation is not the only reason that animals do not speak. They simply don’t have the right brains for it. Karl Lashley, the American psychologist, originally proposed in 1951 that the unique basis of human speech must involve brain circuitry responsible for sequencing movements.44 In recent years, this hypothesis has gained support from the discovery of the FOXP2 gene that governs the embryonic development of brain structures that support speech production. Even if animals could control the required movements, linguist Noam Chomsky emphasizes decoding the underlying structure of language itself as requiring specialized brain mechanisms that humans alone have evolved.45 The major difference between our language and the social communication of other animals is that we have a system of grammar – words and rules that can combine together to generate an unlimited number of new sentences about anything. Most of us are not even aware that we are using these rules. As native speakers, we can spot that there is something wrong with the utterance ‘complex human is language’ because it does not follow the rules, but very few of us know exactly what these rules are. Before we discovered the rules of language, humans were speaking grammatically.
Language is also a symbolic system, which means we use sounds to stand for something. In speech these are the words, but before there were words there must have been specific sounds that we learned to associate with meaning. Animals can also learn to associate sounds to stand for things if they are trained to do so. They can even learn to associate gestures with meanings. There are some famous cases of chimpanzees that learned sign language, but this is not something they can do spontaneously. It requires lots of training with rewards and they cannot make up new sentences as easily as children do.
There is something special about human language in both production and understanding that other animals just do not get because it was never part of their evolution. Our capacity for language is arguably the major species-specific ability that catapulted modern humans into an unparalleled league of social interaction. It has not always been like this. A hunter-gatherer ancestor did not wake up one day and blurt out to the rest of the tribe, ‘Let’s go hunting.’ Our language must have evolved into the complex behaviour that is universally enjoyed today. Some argue that evolution cannot explain something as complex as language but it is precisely because of that complexity that language had to evolve gradually by natural selection. In the same way that the eye is a complex biological adaptation that could not have suddenly appeared from a one-off mutation, the same must be true for language.
Babies do not need to be taught how to speak; most children are fluent by three years of age, irrespective of where they grow up in the world, so long as there are people around speaking to them. The grammars of industrialized societies are no more complex than those of so-called primitive tribes and all languages share the same underlying linguistic rules that were only relatively recently discovered. Language can also be knocked out by certain head injuries, it activates specific networks of neural circuitry in the brain and some language disorders are genetically transmitted. Taken together, these facts indicate that the development of language belongs more to the realm of human biology than cultural invention, which is why language has been called an instinct.46 Language not only enabled humans to pass on information, but it allowed us to domesticate our children by instructing, scolding and encouraging those ideas and behaviours that would be most suited to getting on with others peacefully.
The architecture of the mind
Many scientists believe that language did not suddenly appear but rather must have evolved from a number of different sub-skills – almost like making a new machine by recycling other parts. Evolutionary psychologists Leda Cosmides and John Tooby propose that much of the mind must also be considered like a toolbox that has accumulated specialized skills over the millennia to deal with specific problems.47 Like every other aspect of the human body, they argue that the brain must have evolved to solve problems through the process of gradual adaptation. As Cosmides and Tooby quip, ‘the human brain did not fall out of the sky’, ready prepared to address all of life’s problems. Rather, it must have evolved in stages, dealing with one set of problems at a time. As humans evolved increasingly more complex lives, we also had to evolve new behaviours that provided the best opportunity for reproduction. We needed to find the best mate, refine attentive social skills and learn what was necessary to be accepted.
With these sorts of recurring problems, humans evolved a repertoire of coping skills that are passed on in our genes. Our ability to navigate, count, communicate, reason about the physical properties of objects and interpret expressions are just some of the candidate functions that might be part of our evolved behaviours. These can all be found in humans across the planet today, irrespective of where they live. If these functions are universal and largely independent of the culture or society, then this strongly suggests that they are wired into our biology and transmitted by our genes. However, this is where the theoretical arguments take place. To what extent is a particular human attribute an evolved adaptation and to what extent has it been created and transmitted in recent evolutionary history by culture? Is jealousy a cultural artefact of prevailing sexual attitudes or could it be something that conferred an adaptation in our evolutionary past? Even though we cannot go back to see how our ancient ancestors evolved, we can look for clues that support the idea that functions we possess are the legacy of natural selection.
Human evolution took place over millions of years and must have been gradual for a number of reasons. First, as an organism evolves from simple to more complex activities, the types of problems it encounters over time will change, spurring on the necessity for further adaptations. The complexity of the brain could not have resulted from one massive mutation in our DNA. Rather, the complexity would have had to emerge as each successive version of ancestors had to deal with a new set of problems. Second, adaptation works for solving specific problems, so a brain that was not especially equipped to deal with a problem would not be selected for. In effect, the brain had to have a collection of specialized problem-solving solutions rather than being a good all-rounder. If the brain had only been a good all-rounder problem-solving system, then it could never be as efficient as one made up of multiple specific skills. Different problems require different solutions with tailored mechanisms. In other words, a jack-of-all-trades is a master of none.
One way to imagine the mind is as a Swiss Army knife with lots of blades that perform different functions. You have blades for removing stones from a horse’s hoof (who uses that these days?), corkscrews, scissors and an assortment of other bespoke blades. In the same way, the brain has specific functions such as language, spatial navigation, face processing, counting and so on. If our mind was like our metaphorical knife but only had one general-purpose blade good for cutting but not good for opening bottles, then we would be limited in dealing with specific problems. For example, vervet monkeys have evolved an alarm-call system to identify three different types of predator: snakes, eagles and leopards. Each predator requires a different course of action: either standing on hind legs looking down at the grass around them (snake), looking up in the air and diving into a bush (eagles) or climbing up a tree (leopards). Get the response wrong and the vervet monkey becomes dinner. This is why they instinctively respond to different alarm calls. A general-purpose ‘Look out!’ would not have been a good adaptation.