[Gil]

Vitor: I'm no expert in genetics or anthropology (far from it) but I did study to some extent the History of Portugal and what I can say is that:

"Gothic?
hum...why then, is there less of "I" in the center of the peninsula?"
The answer is simple, because the interlands were more devoided of people than the coastal regions and probably because the south-interior region and the spanish mediterranean coast were deeply settled by invaders.
Note also that "gothic" means the two different types of goths that ruled the penninsula, Visigoths and Suevi/Suebi.

"there was a large influx of dutch (flemish) migrants after the Reconquista.

Hum...and they prefered Portugal?
maybe that is it!"

Well, even Afonso Henriques was the son of a "frenchman":

Henry of Burgundy (1066 - 1112) was Count of Portugal from 1093 to his death. He was the son of Henry of Burgundy, heir of Robert I, Duke of Burgundy, and brother of Eudes I, Duke of Burgundy.
As a younger son, Henry had little chances of acquiring fortune and titles by inheritance, and thus, joined the Reconquista against the Moors in the Iberian Peninsula. He helped king Afonso VI of Castile to conquer modern Galicia and the north of Portugal and in reward he married his daughter Teresa of Leon. With the marriage, in 1093, Henry also became Count of Portugal, then only a fiefdom to the kingdom of Castile. He later was father to Afonso Henriques, First King of Portugal.

Long after Afonso Henriques died the kingdom was deeply unpopulated, specifically the southern regions and the portuguese kings welcomed british, french and dutch (flemish) settlers.