Why are southern Europeans generally of short stature?

[Bloody]

My boyfriend measure 1m89 and his family are more than 1m80, they are all in French Normandy.
France is a country in Western Europe geographically, economically and politically, no southern Europe.
And I not consider the French mediterranean outline as in Southern Europe (as I consider the northern part of Italy at the French border in central europe btw).

North Italy has central European INfluences but is not proper central European like Southern Germany, Austria or German speaking-Switzerland.

North Italy has far more in common with non-mediterranean southern France, in architecture, mentality and peoples. Gallo romance areas.

France is a mid point between Southern Europe and Central Europe. Even Bordering areas in Alsace inmediately feel noticeably different coming from the neighbour cities on the German Border. Northern Italy is Southern Europe. The Germanic world feels very different than the romance speaking world, in time , space , cultures, languages and Peoples.

German speaking Europe + Netherlands/Flanders + Scandinavia = Germanic Europe
Spain+ Italy+ Greece+ Portugal + Southern France = Latin/mediterranean/Southern European culture