Sometimes, just as in real life, there's an imbalance in the gender of babies that are born. In the game that I'm currently playing on my LifeDrive, I've had the opposite problem. For most of the game, I've had only one female, and I've had to carefully take care of her and manage my population to prevent an all-male population. Normally the population isn't quite THAT unbalanced.

All is not necessarily lost, though. There are 3 Island Events that could bring just what you need.