Several research studies over the last few years have started to identify where the lions of North Africa sit in the family tree of lion populations across the globe.
The 2006 paper by Barnett, Yamaguchi, Barnes and Cooper explored how mitochondrial DNA sequences could be used to differentiate lion populations, using ancient samples of known origin. This work included identification of a sequence apparently unique to Barbary lions. These techniques were used to confirm that the lion skulls retrieved from the moat of the Tower of London in the 1930s were in fact Barbary lions (these skulls are now held by the Natural History Museum).
In the same year Burger and Hemmer published mitochondrial DNA analysis of a cub derived from the collection of the King of Morocco, now held at Rabat zoo.
A recent follow-on study by Barnett et al (2014) has continued to show similarities between Barbary lions and Asiatic lions, differentiating them form sub-Saharan African lions.
Matt Walker at the BBC Nature website has written a good summary of the latest research.