Well I do not understand you input "Reverted uncontroversial statement" after reverting my edit. It is very controversial it is out of logic if sombody will not assume the ethnicity diversification (i.e. mix of ethnic group was constant in all time). So as simply as a child can undestand: 
 1. During the history was in Silesia several etnic grups in spend of several hundreds of years. 
 2. They groups did not mix. They appeared and were gone. 
 Conclussion there was not diversity (i.e. mixing) untill XII century BC. I hope it is more clear. Let me know what you do not understand yet.