accidental genetic mutations.............

     The appearance of new ways of thinking and communicating, between 70,000 and 30,000 years ago, constitutes the Cognitive Revolution.  What caused it?  We're not sure.  The most commonly believed theory argues that accidental genetic mutations changed the inner wiring of the brains of Sapiens, enabling them to think in unprecedented ways and to communicate using an altogether new type of language.  We might call it the Tree of Knowledge mutation.  Why did it occur in Sapiens and not Neanderthals?  It was a matter of pure chance, as far as we can tell.  But it's more important to understand the consequences of the Tree of Knowledge mutation than its causes.  What was so special about the new Sapiens language that enabled us to conquer the world?

-Yuval Noah Harari,  Sapiens:  A Brief History of Humankind