If you look in detail at how the English language has been changing over, maybe, the last 50-100 years, it is clear that this is not the case. English is not becoming more standardized; in fact, regional varieties of English are diverging faster now than they ever have been, and this is a measurable effect. (Bill Labov has a lot of research on this, if you’re curious). As it turns out, the mass media has little to no effect on spoken language. People accommodate their language to the people they speak with face-to-face. This is their friends and social circle, not the face on the TV screen.
The “Queen’s English” is not an official standard. It’s also a standardization of spoken English, not writing. The closest thing we have to an “official” arbiter of English usage is the OED, and that’s only official to the extent that it’s generally accepted in academia.
ETA: I assume by “Lycee” you are referring to the Académie française. The Lycée Français is a group of private schools, not a language organization.
I couldn’t have said it any better. 
The “anchor” metaphor and the “substantial body of literature” especially.
Do you think that this ancestral language, assuming it was purely a spoken language with no written counterpart (this is probably a reasonable assumption) was just as complex as languages that are extant today?
Or do you, on the other hand, believe that this ancestral language was somehow more “primitive” than later languages, i.e. modern languages?
Do you believe that a group of people can “lose” the ability to speak? If so, how?
The protolanguages we are able to reconstruct are of comparable complexity to modern languages and attested ancient languages.
What do you mean by this? Do you mean, physically speak, or lose the capacity for language? The sign languages that have developed in various deaf communities are, structurally, languages like any other. So, the capacity for language is not one in the same as the capacity to produce speech sounds.
I meant in the context of a person whose sensory faculties have not been compromised in any way.
For example, if we constructed a diabolical experiment in which we sealed off a city from all outside interaction, killed all individuals older than age 1, and then gave these remaining infants enough food, shelter, and foster care to otherwise grow up physically normal, but prohibited the caregivers from ever speaking to them or exposing them to language in any form whatsoever, would these people develop language during their lifetimes by interacting among each other, none of which were exposed to language?
In such a “population,” could language ever re-emerge? Or have they essentially “lost” the capacity to speak and communicate through any form of language “as we know it”?
What you describe has happened with individual children; it’s called Language deprivation. Children who have not been exposed to language during their childhood seem to more or less lose the capacity to learn or understand language. The general idea is that the brains of children are wired to learn language during a critical period in their development. Once that window has passed, if they haven’t picked up the skills to understand and produce language, they can’t learn it. Genie is probably the best example, and I think there’s plenty out there to read about her. What a sad life 
I think the group of children in your scenario would turn out much the same way as the individual children we have examples of. Since they wouldn’t be exposed to fully developed language in the critical period, they wouldn’t be able to process or produce language well enough to develop it on their own.
It depends how you define “evolution.” “Evolution” implies improvement. The French have the Académie française. Their job is to prevent slang and foreign words from de-volving the French language.
Let’s say, for example, I want to spell school as “skool” from now on. It is shorter, easier to type, and phonetically accurate. Would that be an improvement, or evolution? Or, would it actually make things worse? Therefore, things like dictionaries do prevent changes to a language, but whether those changes are beneficial or not (e.g. misunderestimated, truthiness, etc.) are subject to debate.
In general though, there’s changes all the time (e.g. slang, Valley Girl speak, etc.) and usually there’s a few hundred new words with every new edition of the dictionary, so in general you can’t stop the evolution of language, with or without literacy.
Many new words are created and later discarded with the old word restored. ISTM, that recovering old words should be easier if they’re preserved in written form.
My impression is that English changed much more during the two centuries between Chaucer and Shakespeare than during the four centuries between Shakespeare and Grisham. Am I wrong? If not, why the different rates of change?
Deaf children often develop a limited ‘home sign’ system they use to communicate with their families, even without being exposed to actual sign languages. It would be nothing like a full language and they have the advantage of interacting with language users, who understand the concepts of communication. In Nicaragua, in the 1970s, deaf schools were opened that brought deaf people in contact with each other for the first time and gave rise to a Deaf community. Nicaraguan Sign Language evolved very rapidly (within about 10 years, I think) from an amalgamation of home signs into a complex language. These children had adults present who were language users (but not sign language users), and were actually trying to teach them a language (Spanish), albeit apparently unsuccessfully. Who knows to what degree that helped them. Interacting with each other seems to have been the key factor.
Children like Genie are not really comparable because they have been neglected in so many ways that their development is abnormal across the board.
Actually language is changing all the time, constantly. Whether it’s beneficial or not (evolution vs de-evolution) is the point I’m trying to make.
A conversation I had with my professor circa 2000:
Him: Can anybody give me an example of a new use of word?
Me: “Chair.” Definition: to hit somebody with a chair. As in, Mankind won the match by chairing his opponent.
In all these discussions, the case of the hyper-literate-Jews-with-regard-to-the-Bible (sorry for shorthand) and the revival of Hebrew used by an oral community is of the essence.
Are you asking or demanding that this thread be moved to Great Debates? 
I’m not sure what the 2nd sentence here means. Anyway, I’m sure even OP would agree “prevent” was a poor choice in thread title. The questions is: Do written records slow language change?
One thing that happened after Shakespeare is the standardization of the written language. Examples from Chaucer might look odd because people spelled words the way they pronounced them. If people did that today, it might seem that language did indeed change much more between Shakespeare and now, depending on what variety of English they spoke.
It’s a little dangerous to link language change with a value judgement of good or bad. Is a change good if it increases the utility of the language? Makes the language easier to learn? Makes the language sound more sophistimacated? All of the above?
Was the English of the King James Bible and Shakespeare less useful or was it just different? Does the fact that we have replaced the verb ending “-eth” with “-s” or “-es” represent an improvement in clarity or ease of learning?
That is something we knoweth not!