then it could be argued it should go back to the oldest reasonably cohesive people that had a claim to it at one time, which is probably the Israelis.
Sadly, too many people seem to believe this without being aware of the facts. Genetic analysis indicates that part or the majority of Palestinians come from the native populations of Jews and Christians who converted to Islam during the seventh century. Genetic analysis also indicates that modern day Palestinians and Jews have shared Neolithic ancestors from the region. So, genetics makes it clear that both groups have historical claims on the land.
The difference is that while the Jewish Diaspora occurred, and Jews emigrated to far flung places like Europe, Russia, North Africa, and so on, the people known today as Palestinian continued to reside in roughly the same area. Then, of course, this happened:
http://www.hamdden.co.uk/Images/Palestinian_land_loss_Map.jpg
Palestinians were forcibly displaced to make room for this new creation, and Jews who had possessed no connection to the region for centuries, suddenly migrated from all around the world to the new state.
The Zionist claim to Palestine is about as logical as an Irish claim on the area around the Rhine and Danube, because they are the earliest known centres of Celtish culture. Just because your people may have historically originated from a place, it does not mean you can push people out of their homes to make room because you'd suddenly like to live there again.