What sets human communication apart from lower animals is its compositionality, which means that units of meaning can be combined and new meanings can be constructed. The words "blue" and "car" have their own meanings but combined there is a new content, i.e., a car that is blue.

This kind of ability doesn't actually occur in the animal world. Nor does language. Language is a system of communication specific to humans. Other species can have complex communication. Monkeys have a number of calls and extensive gesture communication but they don't have language because that is based on meaning. There is a vocal form in the case of spoken languages, or a gesture, or a sign, in the case of sign languages, and something distinct which that form means. This kind of relationship between the form and the content is basically absent in the world of animals.

About 2 million years ago there was a breakthrough in human evolution, when a new system of communication emerged, but actual language can't have been more than half a million years ago. Research into the genes responsible for language vocalizations provides support for such an upper limit, while the lower limit is connected by most researchers with the origin of the human species, which occurred about 200 thousand years ago.

If you put people in experimental conditions and forbid them to use language, you can observe what means they will use to start communicating. Research unanimously shows that iconic strategies work best. If you say the word "key", nothing in this form itself suggests which key might be meant whereas if you draw a "key", it has iconicity.

Drawing reflects the things we want to draw our attention to. If we talk about communication in interaction, when you can't always draw, gestures - or more broadly, what we call pantomime - is definitely a better strategy to start communicating than, for example, vocal communication, which is based on more arbitrary forms than gestural communication. It is easier to draw something with your hands than to do it with your voice.

Why is it that today, we mainly talk and not show?

In a recent paper, the authors present a number of arguments for the pantomimic origin of language. We usually associate pantomime with a theatrical genre or a game of puns. However, in the study of language evolution, the view that pantomime was an important link in the evolutionary development of language is gaining popularity. Pantomime usually occurs when people cannot use a language, because they have been experimentally forbidden to do so, or they don't have a common language, or they are unable to use it. 

The researchers studied records from the period of the great discoveries, when the sailors did not know what awaited them in the new land, and yet somehow managed to communicate with indigenous people. The observations on newly emerging sign languages are also interesting, because there you can see how a language is born from the moment when people have no system for communicating with each other, to a fully formed system. Since the 1990s, there have been several cases where researchers have managed to study such a language from its very formation. The best-known case is Nicaraguan sign language. In Nicaragua, there was no language for deaf children to learn and no schools for them. The Americans came and set up a school to teach them American sign language. It turned out that before they did so, the little ones had created their own language. Studies on emerging languages show that at the beginning communication is based on pantomime, on whole-body expression, only later do the proper signs for a given language take shape and the grammar of the sign language develops.

The use of pantomime is also linked to language deficits - for example, in the case of aphasia, when language expression becomes limited due to brain damage, but gestures or pantomime are largely unaffected. This shows that on a cerebral level, pantomime, gestures and vocal language are - at least partly - separate, and people who cannot speak start using pantomime spontaneously, and very often this becomes the basis for language therapy.

Another important feature of human communication highlighted by the researchers of language evolution is multi-modality. When we speak, we also gesture, and we often use, for example, graphic signs in our communication. Very often, traditional narratives creatively combine voice, pantomime and drawing. 

The researchers assume that the primary communication system was an iconic one, with pantomime at its core, which made it much easier to convey meaning. However, elements such as drawing and vocalization complemented it. The development of language was based on increasing the role of vocalization at the expense of pantomime. 

When we start communicating, the iconic form is great, because it's easy to explain something by showing or drawing, but when we have more and more meanings, iconicity becomes an obstacle. For example, it' s difficult to clearly separate kicking the ball from the footballer when using pantomime alone. If we have a general notion of kicking the ball, it's easy to show it, but if we want to show 'footballer' and 'kick the ball' separately, it's not so easy. When we have to convey a growing number of increasingly subtle meanings, the iconicity of the pantomime becomes a limitation for the development of communication, and then we need something more arbitrary, and that is the spoken word.