Within some Aikido circles, I have heard it be said that the jo-staff was representing a spear thus should be treated as if it had a blade at one end. This help explains uke's reactions to some of tori's attacks in the later sections of the goshin no kata. I am having a hard time reconciling a jo with a spear for obvious reasons.
So, my questions is what is the origin of the jo in Aikido? and as an aside what weapon, if any, is the jo meant to represent?.