According to Chomsky, nothing has happened to language in about 50,000 years. Take any child from any place from any time within the last 50,000 years and put him in a family in Boston in 2017 and he will grow up speaking like a Bostonian.
Prior to 50,000 years ago, there was no such thing as language. Something happened in a small space of time that gave us language. Some rewiring of the brain occurred and gave rise to a mechanism. The mechanism is like a snowflake - it is the way it is because nature produces it that way. In the same way a snowflake is need of no further explanation, the mechanism that the brain needed for language is in need of no further explanation. The mechanism occurred in one person and that person then had a capacity to think internally - a proto-linguistic thought process. This proliferated over time and at some later point was externalized in utterances. In order externalize the functioning of the mechanism, the mechanism in the head began to match up with sensory perception. Presumably, such a function was advantageous and so selected by nature in order to advance the species. Eventually, communities with such a mechanism and in which at least one person had begun to externalize the function of the mechanism began to communicate with one another and teach their offspring what we now call 'language.'
Chomsky's picture is attractive for two reasons. First, it posits the least amount of objects and processes possible - just bits of brain, time, and change. This is parsimonious and elegant. Second, it is a perfect fit with naturalism and manages to both distinguish humans from other animals without adopting any grand theory about human dignity that would turn on some metaphysical thesis outside the parameters of the linguist's project.
The trouble is that it is not plausible. How so? For the following reason: although the scratchings on a page and the sounds emitting from a vocal chord are physical, language and its grammar cannot be reduced to anything physical. Chomsky claims that whatever it is in our brains it can only be a physical thing - like a snowflake. But snowflakes don't pretend to have mental properties. Chomsky thinks mental "simply refers to certain aspects of the world, to be studied in the same way as chemical, optical, electrical, and other aspects" (Chomsky and Berwick, Why Only Us? p. 56). Not only is a mental property not the kind of thing one can study like a snowflake, it is not even possible to imagine what a mental object or property might be like to look at. If so, then it is nothing like a snowflake.