It was only meant to be a temporary solution, but the screenwriters believed that his replacement, Dr. Camille Saroyan, fit in better with the team, so she took up his job permanently. (Season 3, Episode 20) Camille/Cam replaced Bones because they wanted to show off more of her skills as a surgeon. They also needed someone who could play off Booth correctly since he's usually the one with the jokes at her expense. Bones has been known to use sexist language from time to time, especially when he's drinking. In fact, this is why they originally wrote down for him to get a female partner. But they decided to go with a person instead so as not to limit himself to just female partners. This is also why they gave Cam an edge over Bones in terms of intellect. She went to medical school while he didn't. Also worth mentioning is that they used to have a female officer named Christine Brennan back in season 1. She died during the first episode of the season though so they can't use her anymore.