Out of the Pyrenees, Alps and Danube, where does the sharpest change in average phenotype occur?

[Ibericus]

There is no genetic gap between both sides of the Pyrenees, meaning there is overlap between northern Spain and Southern France. However, there is a big gap between North Italy and Austria.

[Sikeliot]

Danube is the least. There was much more Slavic influence south of it than Germanic influence south of the Alps.

[Odin]

Alps.

[MysteriousWays]

Danube

[Richard Alvarez]

Contrary to popular belief, I don't think Austrians and Northern Italians look that much different...

[Tooting Carmen]

Contrary to popular belief, I don't think Austrians and Northern Italians look that much different...

That is at least partly explained by the fact that Italy has incorporated provinces which formerly belonged to Austria since WW1.

[Oliver109]

That is at least partly explained by the fact that Italy has incorporated provinces which formerly belonged to Austria since WW1.

Isn't the history of those provinces complicated though? Like how northern Ireland has migration from Scotland before the British settled there.

[Richard Alvarez]

That is at least partly explained by the fact that Italy has incorporated provinces which formerly belonged to Austria since WW1.

I don't even necessarily mean people from South Tyrol, but also ethnic Northern Italians.
I visited Austria and the people there are quite brunette for Germanic standards.

[Straightman]

Definitely the Alps. Northern Italians and Austrians are quite different looking. Danube has not been much of a border between different ethnic stocks even in ancient times, as you had Thracians on both sides of border, then the Roman Empire and later Slavs. Pyrenees are not that an abrupt border either, as you have Basques and Catalans on both sides and Southern French and Iberians are not that dissimilar in general.

[Straightman]

I don't even necessarily mean people from South Tyrol, but also ethnic Northern Italians.
I visited Austria and the people there are quite brunette for Germanic standards.

Yeah sure thing. But could you ever imagine Austrians like Schwarzenegger to pass among Italians?