I do not claim to be an expert on the subject. However, From what I
have read these are the thoughts the I have come up with conderning
ninja. Tenshin Shoden Katori Shinto Ryu , the oldest documented
martial art in Japan dating from the 1400's, includes ninjutsu
training in it ciriculum. It is about 600 years old, while the
Bujinkan claims to have a lineage dating back over 800 years. I
think that the original ninja were actually samurai. Smaurai that
specialized in the ninjutsu techniques of one of the ryu they
studied. Yagyu Jubei is an example. He was a samurai, but is well
known for acting as a ninja. Of course this is just one example.
Durring the Tokugawa period there were a large number of ronin in
Japan. The idea of the freelance ninja probably developed from this
time. Ronin who had been trained in nijutsu techniques would sell
their services, and teach others. This is when ,I think, ninjutsu as
a seperate clandestine art developed. This is also when history and
myths got mixed together and gave the idea that ninja had a long
history. Or maybe the instrustors at that time told their students
that there was a long history. And those histories have been taught
to modern students. Now before I get too many indictments
for "ninjutsu bashing" let me say this. I am not saying ninjutsu
is a good or bad art to train in. I studied ninjutsu myself before I
developed my interest in the samurai. I am only speaking of history
here. For more information this is a good article
http://www.koryubooks.com/library/ninjutsu.html
Dr. Karl Friday holds a Menkyo Kaiden (highest rank possible) in
Kashima Shin Ryu, one of the oldest documented ryu. He is also a
trained historian and is professor in University of Georgia's history
department. Once again I don't claim to be an expert on this so I am
very open to others opinions and inforamtion. Just try to remain
academic and don't get too personal *lol*.