British female scientists want a female Doctor, ostensibly to raise the profile of female scientists in general. Me, I’m just excited about the possibility of Dawkins (himself a guest star on the show and married to a former Time Lady) explain to us the evolutionary biology of a species which gender-morphs male-to-female close to the end of its life cycle.
Because it might explain some things: the Doctor’s preference for female companions, for one. If Time Lords have some hard-coded imperative to sow as many seeds as possible in early life cycles, the Doctor’s just choosing a bunch of partners who look vaguely Gallifreyan and hoping for the best every time he, I don’t know, sneezes on them. He probably knows the futility of his behaviour, and covers it with a lot of “white Time Lord’s burden” stuff about educating humanity, but deep down there are drives at work constantly luring him to hold hands with empty-wombed women. (Consider: why does he never pick up pregnant women? Or sick ones? Why no pre-menstrual girls or adolescent boys? You’d think children would be the most malleable.)
A shift late in life (Time Lord andropause!) might also be somewhat more beneficial if Time Lord pregnancy is as fraught with peril as the rest of Time Lording seems to be. If you manage to make it to your eleventh or twelfth life cycle, it means you must be really, really good at this whole Time Lord thing (or at least surrounded by lesser creatures), and therefore well-prepared to carry another life to term. This comes in handy, as every time the little nipper kicks, he probably creates a minor gravity well somewhere.
Then again, we don’t even know if the female of the species even carries the embryo — Time Lords may be the seahorses of their galaxy. What would really be a kick is if the TARDIS is actually an incubator straight out of Huxley, and that’s why it’s so indestructible. That way, the last of the Time Lords still wins the Darwinian race, despite his dead children and his civilization that he consigned to the flames, because he’s got all he needs to make more. Barring that, we already know that the sonic screwdriver contains enough memory to hold the digitized consciousness of multiple people, so imagining it as an intergalactic turkey baster loaded with Doctor DNA isn’t a big stretch. For all we know, he’s inseminating everything in sight with that thing: hapless Earth women, door knobs, control panels.
Naturally, I know that the real reason the Doctor always has reproductively-available female companions has to do with ratings and tradition. But that doesn’t diminish my desire to have one of those very same companions call him out on it, so we can all watch him squirm as he attempts some semblance of scientific explanation.