If you are one of the people of the Book (whichever book it is), what would you do if this book did not exist? Would you start behaving like any other animals?

No. God doesn't need any book, or any missionaries to regenerate ( "save" ) a human. I would be exactly as I am.
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I would suffer more without the comfort and guidance of the "book". I'd feel lost and alone much more of the time.
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Since we are not living in caves anymore and advanced (somewhat!)as human beings, I feel like I was born with the book of moral and ethics built-in. I understand what you are asking but it is hard to answer. I am not following any particular book but the danger lies in following packs and forming groups and bringing the animalistic side of us to life ( mass hysteria and criminal acts). Animal behavior can exist even while clutching the Code of Conducts to the heart.

I don't think so. I was raised by parents who were "people of the book", but, they were also educated and very moral people. Both were teachers. I would have learned this from them under any circumstances, I believe.

Probably. Books are nothing more or less than racial memory. Without that, language would have little long-term social value. Judging by the decline of American society due to relaxed learning standards over just one hundred years, I'd be inclined to say yes.

It is hard to say, as life is a forward moving journey.