They probably came from the same stock as all the other Indo-Europeans, just earlier and arrived through the Middle east. I suspect they became isolated in Spain - France during the LGM, 18-23,000 years ago and were joined by the rest of the 'family' after the LGM by a group arriving through Russia.
A DNA study that supports this assertion?
UC Davis Study Finds Distinct Genetic Profiles
"The Southern grouping included individuals from Greece, Italy, Portugal and Spain, as well as Ashkenazi and Sephardic Jews. The Northern group included people with English, Irish, German, Swedish and Ukranian ancestry."