“They must be related through history.”
They are.
“Is it possible that baptism is an age old declaration of faith that was practiced before Jesus?”
In a sense, yes, but more of a declaration of repentance and purification.
“Did Jews appropriate the ceremony after him?”
No, they had it BEFORE Jesus walked the earth in His three years of ministry. http://jewishencyclopedia.com/articles/2456-baptism
http://www.christianitytoday.com/ch/asktheexpert/mar14.html
Thank you!!