Rishis have been there in every age; there are many stories about them. A Rishi is like the Dean, or the Vice Chancellor of a University. They also underwent training, and then became part of the tradition.
So, like how you say, ‘I am an Alumni of Harvard’, or ‘I am a Stanford graduate’, similarly, there are Gotras. Go means knowledge, and Gotra means, belonging to a particular knowledge group or Rishi tradition. So, just like we have different DNA or blood groups, we have different Gotras or families that come from certain knowledge groups, or Rishi traditions.