Actually clowns are born not having a designated sex as gooyferret stated. As they mature and pair, the larger will become female and the smaller male. In the wild, they will stay in small groups where the female inhabits the host and the male tends to her and protects the area. The others will in fact stay nueter until the time come when one of the other two dominats of the group dies. If that's the female, the male will become the new female and one of the nueters will become male. In most all cases that will be the largest of the group.
If left solitary, most clowns will become female after a time. As a male they can become female. Once a female though, that's it.
Cheers
Steve