Why Northern Italians are so different from Southern Italians?

[manu15151513]

The Ancient Greek influence in Southern Italy was essentialy greater than the Levantine
http://explorethemed.com/SicilyClass.asp?c=1
http://www.bestofsicily.com/mag/art153.htm

Sicilian males have about 30% Greek YDNA still today

Sicily has more Greek ancestry than any other part of Italy

I do not think so, it seems that those who mostly come from the colonists of great Greece are the Pugliese and the Sicilians of some areas. The colonists of Great Greece were mostly Achaeans, ions and Dorians, hence Indo-Europeans, presumably they often had a phenotype recalling the idea of ​​the Nordic.
Southern Italians are quite distant from many continental Greeks, the resemblance is extremely strong with the island ones. As for the autosomal, the ancient Levantine autosomal inheritance is undoubtedly stronger and the Italians of the South have an autosomal mixture much closer to the Greek islands than to those of the continent. If they derived much more from the colonists of Great Greece, they would be more Nordic genetically and less inclined to the east. What genetically links the island greeks and the southern Italians in large part the similar relevance that have covered ancient gene flows in defining their autosomal mixtures. The Sicilians closest to the Greeks would seem to be those of Syracuse. Haplogroups are less important than the autosomal in determining the ancestral origins of a people.