I'm currently reading the book [1] and while I haven't finished it yet, the thrust (if I'm understanding it correctly) seems to be that it was the increasing complexity of civilization (as populations rose in an area) that lead the brain to reform connections to be less bicameral in nature.
There are evolutionary changes in humans that are known to us. For instance, people of European descent can still digest milk into adulthood; the father you get from Europe, the greater that lactose intolerance grows. So it could also be for bicameralism.
I too, am skeptical about how this came across the world, but he does mention in passing that some of the Pre-Columbian cultures of North America could have still been bicameral as late as the early 1500s. It's really an interesting read.
[1] I found a copy in a used book store and the price was right.
There are evolutionary changes in humans that are known to us. For instance, people of European descent can still digest milk into adulthood; the father you get from Europe, the greater that lactose intolerance grows. So it could also be for bicameralism.
I too, am skeptical about how this came across the world, but he does mention in passing that some of the Pre-Columbian cultures of North America could have still been bicameral as late as the early 1500s. It's really an interesting read.
[1] I found a copy in a used book store and the price was right.