My basis of assertion: Mahabharata is like the Bible. Who here can claim to have seen the original version of Mahabharata? Anyone? It was written, rewritten and in the process of writing/rewriting people added their own views/things. It certainly didn't happen in Dwapar Yug, nor Vyasa wrote it and had exclusive copy right for it. Someone in Northern India or Nepal wrote it, it became popular and the people in this region started adding things to it. For example, the oldest copy of Mahabharata was in Nepal, at Bir Pustakalaya, Ghantaghar ko.. during the 60s it was loaned to the Bhandarkar Research Institute of Pune, India, from where it never came back. The Mahabharata we saw on TV was based on the Bhandarkar Institute's Mahabharata, which happens to be the Nepali version of Mahabharata. And I don't think the Mahabharata we had at Bir Pustakalaya, which I haven't see myslelf, was 1500 years old. It wa sprobably 700-800 years old, and 1500 to 700 eyars time, you have 800 years gap and in the 800 years gap, people altered it by adding their own stuff.. and its probably then it became 100000 verses epic. And its probably then, people added the Geeta to it. If it was old, then the people we would have had people who wrote the upanishads discussing and writing multiple views on the geeta too, hoina? So, both Mahabharata and geeta have to be new, when the old philosophical reasoning school of hindusim had died out and more deuta believing school had taken over.