Ok, so how do 2 people from opposite teams look alike? Simple, some are clones, some are original In the beginning, there was one class per each team. There was only a Blu Engineer, Blu Soldier, etc There was only a Red Heavy, Red Demoman, etc Now both teams saw how threatening the other mercenaries were. So they decided to clone the entire team of the opposition.

Have you noticed in the webcomics, when a class gets a backstory, its only from one team(although this is justified). No backstory for the RED engineer, just BLU. No limelight for the BLU demoman, only the RED. And unless They make comics for them(which, in hindsight, would be stupid) , it proves my point even further.

http://en.wikipedia.org/wiki/Parallel_evolution

LET'S TURN THIS INTO A BIOLOGY BATTLE.