Of course. It's the evil twin syndrome. It's extremely likely that not only would they be complete opposites, but they may have certain genetic defects that probability factors (or, to the laymen, 'luck') have kept some of us from having. Not only do circumstances dictate a 'turn left' situation for us physically, but organically as well, in so forth that anything at all could be different on the microscopic level as well as the physiological.