Who are the Catalans? And why are 25% of them Rh Negative?

Just like Basque Country, Catalonia is an autonomous region in northern Spain. Catalonia is bordering France in the east while the Spanish side of Basque Country does so in the west.
Recent studies have revealed that about 25% of Catalans have the rh negative blood factor.
Catalans also have on of the highest percentage of the y-DNA marker R1b, associated with Celtic DNA.

There are quite a few famous Catalans.
One of them is Soprano Montserrat Caballe, featured here with Freddy Mercury:

Another one is super surrealist Salvador Dali.