Europe, throughout most of its history, was a corner of the world. It was a final destination for tribes that were misplaced by overpopulation, decease, and fam

Europe, throughout most of its history, was a corner of the world. It was a final destination for tribes that were misplaced by overpopulation, decease, and famine from the Middle East and Central Asia. My theory is that in order for this mutation to spread it must give a cutting edge advantage in an equal environment. However, the migration pressure was toward Europe, not out of it. What's more, other populations already had their ways to utilize derry products and the advantage might not have been so crucial. Therefore, the gene spread had been dependent mostly on internal migration and local populations mixing together. Of course, this theory has its weaknesses. It does not account for the effects of Alexander the Great, the Silk Road, the Roman empire or the depopulation of Eastern Europe through slave trade during the middle ages. At the same time, most of these factors would open trade routes and cultural exchange but not the large scale migrations necessary for a significant genetic mix. Slavery might offer something, but it was recent and slaves are usually the most disadvantaged group in a society which does not help their genes being promoted.