The foregoing gesture examples may all seem plausible, but that doesn’t make them correct. “Correctness” in this case means whatever is naturally learnable.
Linguists have a very specific definition for the phrase “naturally learnable”. It doesn’t mean something that can be learned through conscious practice and study. Rather, it means something that one learns even without conscious practice or study.
For example, one’s native spoken language is naturally learnable. We didn’t need to go to school to learn our first spoken language — we began to gradually speak it when we were still young children, simply by being exposed to it.
In contrast, written language is not naturally learnable. Most people need to put in the effort required to consciously study and practice before they can read or write effectively.
Attempts to create a synthetic “natural language” generally fail, in the sense that children will not learn them. For example, when children are exposed to Esperanto, they will spontaneously try to alter it, because its rules violate their innate instinct for natural language.
There is now a general consensus amongst evolutionary linguists that natural language and children below around the age of seven are a co-evolution: Natural language evolved to be learnable (and modifiable over time) by little children, while simultaneously little children evolved to learn and modify natural language.
Tomorrow we will discuss what this means for our topic of future language.