Male, the doctor has always been male and has shown no inclination to become a female. It also removes a role model for young boys with someone who doesn't employ violence to solve problems.
In addition it's fully clear that a female doctor is a "stunt casting" to try and boost ratings. While it would do it for an episode or two I think you'd see ratings slide further once the "newness" is done.
I mean, I love the show and I'll keep watching but I don't think a female doctor would last a full 3 (or more seasons) before being replaced. My sarcastic response is "if they make a female doctor I demand a Wonder Man movie".
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