>> The simplest explanation is their diffusion ~15,000 years ago. The problem I have with that is everything started to change when the glaciers started meltin

>> The simplest explanation is their diffusion ~15,000 years ago. The problem I have with that is everything started to change when the glaciers started melting. Civilization surely extended to areas that we now call the continental shelf. Sea levels gradually rose several hundred feet, washing away an awful lot of everything. It's hard to say what was where and diffused because there isn't there any more.