[Master] (To be boringly pedantic, it is one of those minor little traits that seem to be mostly random in the history of our biology, and you'll probably encounter variance from universe to universe, but did I mention boring? Science without application is all well and good, but I find I care less for theory these days.)

Keep in mind also that everything you've seen (and, in fact, everything you're seeing now, despite efforts to the contrary) has been presented through a human lens, which will tend to take for granted the similarities between species and brush off or sensationalise the differences.

And while there is a subset of Time Lords who base attraction on physical characteristics, for a large and growing number of Time Lords I'm sure you can see how this would be an unstable proposition at best. (You can compare it, if you'd like, to a human condition predicating attraction on age or some such other transitory state. Paederasty (http://en.wikipedia.org/wiki/Pederasty) provides one such suitable example.) (Unstable especially as regards the Doctor. Have you seen what he does to himself?) (Well, the Doctor is difficult to deal with in a number of regards.)

Gyuh. While I'm aware that the current Earth vogue is to go about claiming "sexuality" is such a broad, vague term, it's nonetheless too specific to apply with any real sense of accuracy to Time Lords. If you want any real answers, you'd do well to refine your questions a bit.