It's well known that around 40% of men on the island of Sardinia belong to the I-M26 paternal haplogroup, but which subgroup? And can that tell us anything about where M26 originated? Did M26 people expand "out of Sardinia"? Or did M26 arise on the continent, and a few M26 made it to Sardinia early in its human history?
It's starting to look like the second scenario is closer to what happened. The I2a Project at Family Tree DNA (FTDNA) has around 8 I-M26 members who were born in Sardinia, or who have fathers or grandfathers born in Sardinia. From testing at FTDNA we know that they are all likely L160+, the I-L160 group is the most common group of I-M26 but there are several L160- branches known only from continental Europe and Britain and Ireland. The design of the new Genographic 2.0 test involved sequencing several men living in Sardinia, so it includes many new SNPs relevant to these men. So far, one Sardinian-American man and one Maltese ancestry man belong to the PF4190 branch of I-L160. I think probably many or most I-M26 men living in Sardinia will belong to this branch, but we will need more testing to be sure.