Prehistory was punctuated by massive waves of migration that resulted in a new population moving into a region and almost completely wiping out the previous inhabitants. Nearly always, the migrants were unwittingly aided by an invisible but devastating weapon of mass destruction: infectious diseases to which they were to some extent immune but to which original communities had little or no resistance. In addition to novel pathogens, Neolithic immigrants brought new genes, new languages and new ideas such as farming and metallurgy.
