This map covers over 300 miles in diameter and 3-4 different ethnic groups from Czechs (Germanic) to Montenegro (Mediterranean) to more Slavic in the central and east. The only reason they were brought together was the Yugoslavian republic. That has a lasting impact.

If you look at the distribution of the best Beach Volleyball players it would be a strip of about 10 miles from Santa Monica to Manhattan Beach. Does that mean that there is some genetic abnormality in the South Bay that produces people who can jump better in the sand? No, it's just where the game was invented and, more importantly, developed and supported and where people could make money playing the sport.