Okay, I figured out whats going on.
See.. with Tommy Boy being infertile, he wanted to do a sneaky artificial insemination without the public knowing so they would think he was "a big man", right? Well, he decided that his best buddy would be a great donor.. John Travolta, same coloring and hair color. Told the doctor that his best buddy was stopping by to donate. Unfortunately his OTHER best buddy, Will Smith stopped by to visit, the doctor got confused.. Will being the nice guy always wanting to help....
Badaboom Badabing, 9 months later they are looking at a dark skinned baby with ears that rival an elephant and wondering what went wrong.